∆Chem 101L Overall Review∆

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Weighing by difference

A method to find the weight of a sample by subtracting the amount of sample removed from the weighing container rather than the amount of sample added to it.

Calculations for Experiment 2: Aqueous Reactions

(Grams of solid reactant) * (inverse of molar mass of solid reactant) = (Moles of solid reactant) (Final Temperature) - (Initial Temperature) = (Change in temperature) (Change in temperature) / (moles of reactant) = (Change in temperature / moles of reactant)

Reminders for measuring by difference

(Initial mass or volume)-(Final mass or volume) Remember that your answer should have the same number of decimal places as the number given in the scenario with the lowest number of decimal places to adhere to sig figs! (Addition/Subtraction rule)

Dilution equation

(M1*V1)=(M2*V2) V is volume, M is molarity

Calculations for Experiment 1: Mass, Volume, and Density

(Mass of buret with sample) - (Mass of buret) = (Mass of water) (Largest volume increment) - (Displaced Volume) - (Volume reading with thermometer) = (Corrected Volume) (Mass of water) / (Corrected volume) = Density [ (True Value) - (Mean) ] / (True Value) = (% error)

Calculations for Experiment 4: Conductometric Titrations

(Volume of barium hydroxide) * (Molarity of Barium Hydroxide) * (Molar ratio) * (Inverse of molarity of sulfuric acid) = (Volume of sulfuric acid) (b2 - b1) / (m1 - m2) = (Volume of titrant extrapolated at minimum conductivity) (Volume of sulfuric acid at minimum conductivity) * (Molarity of sulfuric acid) = (Moles of sulfuric acid)

Calculations for Experiment 6: Thermochemistry

(mliq) + (msolid) = (msoln) qcal = (ccal) * DT

The graph shows the calibration of a spectroscope against a series of emission lines of known wavelength. Based on this calibration, which is the wavelength of a line that appears at 4.71 mm on the spectroscope scale? (PIC ON OTHER SIDE) Select one: a. 362 nm b. 0.603 nm c. 479 nm d. The answer cannot be determined from the information given e. 470 nm

***c. 479 nm

Potential source(s) of significant error in Experiment 5 include: I. Using an excess of yeast in the reaction with H2O2. II. Using an excess of H2O2 in the reaction with yeast. III. Using an excess of HCl in the reaction with zinc. IV. Using an excess of zinc in the reaction with HCl. V. Losing H2 gas because it is much less dense than air. VI. Losing O2 gas because it is much less dense than air. VII. Collecting gases while the reaction is still hot, resulting in mostly H2O vapor in the bulb. VIII. Collecting both gases in the same pipette bulb. Select one: A. Only V and VII are correct. B. Only V, VI, and VII are correct. C. All but II, III, and VIII are correct. D. II, III, and VIII are correct. E. All of these are sources of error.

**A. Only V and VII are correct.

In Experiment 7, the purpose of creating the Beer's Law plot of absorbance vs. concentration of Allura Red AC is best described as: Select one: A. to determine the mg/serving of Allura Red AC in a solution prepared from a soft drink sample. B. to determine the molar concentration of Allura Red AC in a solution prepared from a soft drink sample. C. to follow the progress of the reaction between Allura Red AC and water. D. to demonstrate the linear relationship between the concentration of a solution and it's absorbance.

**A. to determine the mg/serving of Allura Red AC in a solution prepared from a soft drink sample.

In a conductivity titration, 10.15 mL of 4.95 x 10-3 M Ba(OH)2 is titrated by a 4.15 x 10-3 M H2SO4 solution. The end point of the titration would be expected at a volume of: A. 10.15 mL B. 12.11 mL C. 0.002024 mL D. 6.053 mL

**B. 12.11 mL

When viewed through a spectroscope, calcium ions produce three distinct lines in the visible region of the spectrum, at spectroscope positions of 7.30, 7.85, and 8.45. Assuming the linear fit for the calibration of the spectroscope has a positive slope, the line corresponding to the highest energy would have a spectroscope position of: Select one: A. 7.85 B. 7.30 C. 8.45 D. The answer cannot be determined from the information provided.

**B. 7.30

During a conductivity titration, 15.0 mL of Ba(OH)2 is placed in a beaker with 35 mL of H2O. At the start of the titration, the initial conductivity reading is nearly double that of a previous trial and does not decrease to zero at the minimum as expected as sulfuric acid is added, even though the minimum occurs at the expected volume. One possible explanation for these observations would be Select one: A. The barium hydroxide and sulfuric acid were mistakenly combined in the beaker, and the water was used to fill the buret. B. Instead of adding distilled water to the barium hydroxide, the experimenter added tap water. C. The experimenter mistakenly added twice as much barium hydroxide to the beaker. D. The sulfuric acid was added to the beaker while the barium hydroxide was used to fill the buret.

**B. Instead of adding distilled water to the barium hydroxide, the experimenter added tap water.

Given the Rydberg equation: ΔE = RH (1/(nf2)- 1/(ni2)) In the Balmer series for hydrogen, what is the initial energy level (ni) for a photon with a wavelength of 656.3 nm? REMEMBER: h = 6.626 x 10-34 J⋅s; c = 2.998 x 108 m/s; RH = 2.18 x 10-18 J Select one: A. 1 B. 2 C. 3 D. 4 E. 5 F. 6 G. The answer cannot be determined from the information given.

**C. 3

A 1.00-mL sample of a soft drink is diluted with distilled water to 3.50 mL in a cuvet. The concentration of the diluted solution is determined to be 4.58 x 10-6 M in Allura Red AC. Based on this result, what is the mass of Allura Red AC in a 946-mL sample of the drink? (NOTE: The molar mass of Allura Red AC is 496.43 g/mol.) Select one: A. 0.615 mg B. 615 mg C. 7.53 mg D. 7.53 g E. None of these. F. 2.15 mg

**C. 7.53 mg

Which Lewis structure best corresponds to the condensed structure given by CH3(CH2)2CO2CH3?Select one: (PIC ON OTHER SIDE) a. Both I. and III. are possible. b. III. c. II. d. I. e. IV. f. Both II. and IV. are possible. g. None of these.

**d. I.

For the reaction of 3.5 g of sodium bicarbonate with 30 mL of 0.5 M HCl if the temperature rises from 22.4°C to 32.1°C. The value of ΔT/mol (°C/mol) would be:

233 Degrees C/mole 32.1-22.4=9.7 3.5 g NaHCO3 * (1 mol/84.02) = .042 mols 9.7/.042 = 233

Room Temperature

25 degrees C or 278K

The molecular equation for the reaction in Experiment 4 is: Ba(OH)2 + H2SO4 →BaSO4 + 2 H2O How is conductivity reflected in the net ionic equation? A. Barium hydroxide and barium sulfate are soluble ionic substances that will ionize in solution and be conductive, but sulfuric acid is a covalent molecule that is nonconductive, as is water. Therefore, barium ions are the only spectator ions and will not appear in the net ionic equation. B. Barium hydroxide and barium sulfate are both ionic solids that are nonconductive, and water is a covalent substance that is nonconductive, but sulfuric acid is a strong acid that is highly conductive in solution. Therefore, there are no spectator ions and the net ionic equation will have H+ and SO42- ions on the reactant side. C. Barium hydroxide is a soluble ionic substance that is highly conductive in solution, and sulfuric acid is a strong acid that also conducts strongly in solution. In contrast, barium sulfate is an ionic solid, and, as a solid, it is nonconductive. Water is a covalent substance that is also a nonconductor. Therefore, the net ionic equation will have no spectator ions, and only the reactants will be written as ions in solution. D. In this experiment, barium hydroxide and barium sulfate are soluble ionic substances that will ionize in solution and be conductive. Sulfuric acid is a strong acid that ionizes in solution and is conductive. Water is a covalent substance and is nonconductive. Thus, barium ions and sulfate ions will be spectator ions and will not appear in the net ionic equation.

**C. Barium hydroxide is a soluble ionic substance that is highly conductive in solution, and sulfuric acid is a strong acid that also conducts strongly in solution. In contrast, barium sulfate is an ionic solid, and, as a solid, it is nonconductive. Water is a covalent substance that is also a nonconductor. Therefore, the net ionic equation will have no spectator ions, and only the reactants will be written as ions in solution.

To carry out Experiment 6 quantitatively, one major adjustment was made to the procedure followed in Experiment 2. That adjustment was Select one: A. Calculations were made in moles rather than in grams. B. All solutions were equilibrated to room temperature before beginning the experiment. C. The calorimeter was calibrated to account for heat loss from the system. D. The thermometers were calibrated to give accurate temperature readings in °C. E. None of these is true.

**C. The calorimeter was calibrated to account for heat loss from the system.

In a determination of the mass of Allura Red AC in one serving of a food sample, the result is found to be ~10% too high when compared with another determination. The most likely experimental error to explain this result would be: Select one: A. When the 1 x 10-5 M stock standard was prepared, instead of transferring 500 microliters of the 2 x 10-3M stock to the 10.00-mL volumetric flask, the experimenter transferred 550 microliters. This increased the slope of the calibration line by 10%, causing the sample solution concentration to be calculated 10% too low. B. All of these answers could explain the error in the results of the determination. C. The pipet used to dilute the sample measured 10% too much of the sample, so the transmittance was measured lower than the actual sample transmittance, and produced a higher calculated mass. D. None of these answers explains the error in the results of the determination. E. When the 1 x 10-5 M stock standard was prepared, instead of transferring 500 microliters of the 2 x 10-3M stock to the 10.00-mL volumetric flask, the experimenter transferred 450 microliters. This decreased the slope of the calibration line by 10%, causing the sample solution concentration to be calculated 10% too low.

**C. The pipet used to dilute the sample measured 10% too much of the sample, so the transmittance was measured lower than the actual sample transmittance, and produced a higher calculated mass.

3.5 g of white crystalline solid is added to a calorimeter containing 30 mL of water at 22 °C. During the reaction, the solid crystals disappear and the temperature of the solution decreases. Based on these observations the reaction would be classified as: A. precipitation B. acid-base C. endothermic D. gas-forming E. none of the above F. two of the above

**C. endothermic

The temperature at the start of a reaction was 22.8°C and the final temperature was 32.9°C. Based on these observations, the reaction of sodium bicarbonate with hydrochloric acid would be: A. endothermic, because energy is transferred from the reaction to the surroundings. B. exothermic, because energy is transferred to the reaction from the surroundings. C. endothermic, because energy is transferred to the reaction from the surroundings. D. exothermic, because energy is transferred from the reaction to the surroundings.

**D. exothermic, because energy is transferred from the reaction to the surroundings.

In a calorimetry experiment, 50.0 mL each of two dilute aqueous solutions are combined and produce an extrapolated ΔT = 22.4˚C. If the density of each solution is assumed to be equal to that of water (at 20˚C, d = 0.9982 g/mL), and the specific heat of the solution is also equal to that of water (4.186 J/g˚C), the value of qrxn would be: Select one: A. -17.7 kJ B. 9.38 kJ C. 17.7 kJ D. -9.38 kJ E. -9.36 kJ F. 9.36 kJ

**E. -9.36 kJ Correct

A Beer's law calibration curve for a particular analyte has a best-fit equation of A=(11765 M-1)C + 0.197, with an R2 value of 0.9373. If a sample solution has an absorbance reading of 0.811, the concentration of the unknown sample would be: Select one: A. 0.0537 M B. 0.0472 mM C. 7.35 x 10-5 M D. 0.0907 mM E. 0.0472 M

**E. 0.0472 M

In the reaction KOH(s) + HBr (aq) → KBr(aq) + H2O(l), the spectator ion(s) would be: Select all that apply: A. HBr B. KOH C. OH- D. H+ E. Br- F. H2O G. K+ H. There are no spectator ions in this reaction. I. KBr

**E. Br-

Based on your observations in Experiment 5, an exothermic reaction may be identified via observation in the lab when it: A. Produces bubbles. B. Dissolves a solid reactant. C. Three of these answers are correct. D. Causes a loud popping noise. E. Two of these answers are correct. F. Forms a precipitate. G. Grows cold. H. Causes water condensation farther downstream

**E. Two of these answers are correct.

A conductivity plot for the titration of barium hydroxide with sulfuric acid is shown below. Assuming sulfuric acid is the titrant, which ion species would you expect to be significant in solution when 8.62 mL of titrant had been added? (PIC ON OTHER SIDE) A. Ba2+ B. SO42- C. H+ D. OH- E. A, B, and D. F. B and C only. G. A and D only. H. None of these

**G. A and D only.

The following equations represent reactions used in Experiment 5. Of these reactions, choose the correctly balanced oxidation-reduction reaction. Select one: A. 2 H2O2 (aq) + catalase → 2 H2O (l) + O2 (g) B. None of these is correct. C. 2 H2O2 (aq) →catalase→ 2 H2O (l) + O2 (g) D. H2 (g) + O2 (g) → H2O (g) E. HCl (aq) + 2 Zn (s) → H2 (g) + ZnCl2 (aq) F. H2O2 (aq) →catalase→ H2O (l) + 2 O2 (g) G. H2 (g) + 2 O2 (g) → 2 H2O (g) H. 2 HCl (aq) + Zn (s) → H2 (g) + ZnCl2 (aq)

**H. 2 HCl (aq) + Zn (s) → H2 (g) + ZnCl2 (aq)

In calorimetry, the enthalpy change of the reaction, qrxn, is defined to be: (Select all that apply.) A. -(qsoln + qcal) B. qcal -qsoln C. qsoln -qcal D. ΔH / nreagent E. the heat gained or lost by the reaction in units of joules. F. the heat gained or lost by the reaction in units of joules/mol. G. the difference between the extrapolated maxiumum temperature and the initial temperature in a reaction. H. qsoln + qcal I. Both A and E are true. J. Both D and F are true.

**I. Both A and E are true.

Which of the following is a true statement about the bright yellow flame seen during a flame test of a 1 M solution of NaCl in a Meker burner flame? Select one: a. The yellow color is characteristic of the temperature of the Meker burner flame. b. The yellow color is characteristic of the changes in energy of an electron in the Meker burner flame. c. None of these is true. d. The yellow color is characteristic of the changes in energy of an electron in the Na+ metal ion. e. The yellow color is characteristic of the changes in energy of an electron in the Cl- anion.

**d. The yellow color is characteristic of the changes in energy of an electron in the Na+ metal ion.

According to the stoichiometry of the exothermic reaction equation 2 HCl (aq) + Mg (s) → H2 (g) +MgCl2 (aq), the maximum energy that can be released by this reaction would occur at a HCl:Mg ratio of a. 1:1 b. 2:3 c. 1:2 d. 3:2 e. 2:1 f. The answer can't be determined from the information given.

**e. 2:1

Which explanation of the structure of pentane best predicts its solubility in water? (PIC ON OTHER SIDE) Select one: a. The Lewis structure shown in (I.) shows that the polar C-H bonds are symmetric and will cancel out, leaving no molecular dipole. Therefore, pentane will not be soluble in water. b. The model result in (II.) shows that the H-C-H bond angles are not 90°. This means that the C-H bond dipoles cannot completely cancel out, so pentane will be soluble in water, but its solubility may be limited. c. The model result in (II.) gives a molecular dipole of 0.055 Debye, which means that diethyl ether will be strongly soluble in water. d. The Lewis structure shown in (I.) shows that the polar C-H bonds are symmetric and will cancel out, leaving no molecular dipole. Therefore, pentane will be soluble in water. e. VSEPR theory applied to the structure in (I.) predicts that the H-C-H bond angles will be 109.5° rather than the 90° shown in the Lewis structure. However, the C-H bonds are fully symmetric and have no significant bond dipole, so pentane should be insoluble in water.

**e. VSEPR theory applied to the structure in (I.) predicts that the H-C-H bond angles will be 109.5° rather than the 90° shown in the Lewis structure. However, the C-H bonds are fully symmetric and have no significant bond dipole, so pentane should be insoluble in water.

Consider the following compounds: I. n-pentanol CH3(CH2)3CH2OH II. pentanal CH3(CH2)3CHO III. ammonium pentanoate CH3(CH2)3CO2NH4 IV. pentanoic acid CH3(CH2)3CO2H Which would you predict would have the highest conductivity in solution? Select one: a. II. b. I. and II. will have equally strong conductivity c. IV. d. None of these will have any measurable conductivity because none is soluble. e. III. and IV. will have equally strong conductivity f. III. g. I. h. All of these will be equally soluble.

**f. III.

Ionic for Molecular vs NIE

*NIE*: covalents are written as whole molecules!! (CO2, H2O, etc.) molecular: full reaction Ionic: broken up ionic compounds NIE: cancel out the spectators

In calorimetry, the enthalpy change of the reaction, qrxn, is defined to be:

- -(qsoln + qcal) - the heat gained or lost by the reaction in units of joules.

Define absorbance, transmittance

- Absorbance - how much light does not get through - Transmittance- how much light gets through the cuvette

enthalpy

- Change in heat between reactants and products -*State function= independent of path*

Equipment to recognize and understand correct procedures for use (and safety): colorimeter, cuvette, Bunsen burner, micropipette, graduated pipette and bulb, volumetric flask.

- Colorimeter- must press stop before opening. must calibrate - Cuvette- Has two sides you can handle, two you cannot, do not wipe inside - Bunsen Burner- base can get very hot, do not leave open flame - Micropipette- push once to pick up, all the way down to release - Graduated pipette and bulb- middle button picks up, top releases all air, side releases liquid - Volumetric Flask- fill to line mL

Define the concept of calibration and its application to this experiment.

- Correction factor applied to make measurements on an unknown system - Used to determine factor in the heat leaked from the calorimeter

molar extinction coefficient

- How strongly the analyte absorbs light at a particular wavelength - Different for each and every wavelength and analyte

What are the most likely sources of uncertainty in this experiment? What variables are difficult to control or minimize? What are the technical challenges to measuring an accurate and precise result?

- It was difficult to control how quickly the reaction would occur depending on how well it was mixed - The apparatus released heat to the environment - The Sodium hydroxide Pellets absorbed moisture from the air easily so the mass may have been off

What reaction/reagents were used in this experiment? What properties of these materials made them especially suited to this experiment? What properties of this materials made working with them challenging? E.g. what is the purpose of measuring mass by difference when using solid NaOH pellets? Is the experiment affected in some way by beginning with a solid reagent rather than a solution?

- NaOH-->dissolves, basic, dissolving takes time - HCl-->acidic, neutralizes base - Challenging- difficult to work with because it was hydroscopic - When starting with a solid there is a period in which not all of it will dissolve

How is the energy change in a reaction measured from a graph of temperature vs. time? What temperature change would be expected for an exothermic reaction? Endothermic reaction?

- Over time the temperature increases until the reaction has finished then it will drop off again. - exothermic= If temp. of surroundings increased - endothermic= if temperature of surroundings decreased

exothermic

- Products are at a higher energy than reactants - Releases Heat

endothermic

- Products are at a lower energy than reactants - Absorbs heat

Identify key regions in the graph that are used for analysis. Where are linear fits are used, what is the expected slope? What is happening at the molecular level that leads to that behavior? If the correct behavior is not seen, what might be happening to explain the result?

- Put trendline through the values after the temperature begins to decrease again and plug in the time of mixing for x to solve for y the maximum temperature at mixing. The first temperature data point is the initial temperature. - The expected slope should be negative since the graph has hit its maximum - Atoms will start to move slower so the temperature will start decreasing after the maximum

What are the key features of a Beer's Law plot? Identify key regions of the plot. What is the value of plotting these data individually rather than averaging values for the standard curve?

- The curve helped us identify the unknown concentration by giving a set plot - Slope equates to the product of the molar extinction coefficient x path length. - Intercept represents background signal not associated with analyte. - Correlation coefficient is equal to R2 value. - Better not to average because it give us an idea of where the unknown concentration will fall

How is the energy change in a reaction measured from a graph of temperature vs. time? What is the relationship between energy and temperature?

- The temperature increase is graphed over time - An increase in temperature indicates an increase in energy

pyrolysis

- burning and drying colorimetry - an instrumental method based on the measurement of light absorption by colored solutions and is widely used for performing chemical analysis

stock solution

- diluted FeCl3 - a concentrated solution that will be diluted to some lower concentrated for actual use.

When using a colorimeter, what factors could lead to an incorrect reading (e.g. bubbles in the cuvette, etc.)? What effect might these errors have on the result?

- dirty on outside - bubbles in cuvette - incorrectly calibrated

Net ionic equation

- ignore spectator ions and only focus on participating ions Ex. w/ NaCl(aq) and AgNO3(aq) Cl-(aq) + Ag+(aq) -> AgCl(s)

colorimetry

- instrumental method based on the measurement of light absorption by colored solution and is used to perform chemical analysis

Interpret the quality of the standard curve based on experimental data, and anticipate the effect of errors in the standard curve on the results of the experiment. What is the purpose of making multiple measurements of each standard solution?

- linear regression represents calibration curve - Making multiple measurements improved the accuracy (helps incase one side of the cuvette is scratched or blocked)

Define Beer's Law verbally and be able to describe the usefulness of this concept in making measurements of chemical species and properties.

- tells us how much there is of something - relates absorbency to concentration - defines how strongly the solution being studied absorbs light at a particular wavelength. - This is unique for each different chemical at each different wavelength. - The quantity of light absorbed by a substance dissolved in a nonabsorbing solvent is directly proportional to the concentration of the substance and the path length of the light through the solution

Why was 0.1 M HCl used as the blank in the colorimeter? What would it mean if the blank turned faint red after adding NaSCN? How might this affect the results? What should an experimenter do to correct it?

- this means that HCl may have had some Fe3+ n it and this would make it not 100% transmittance. - Correct by adding HCl?

In calorimetry, the enthalpy change of the reaction, qrxn, is defined to be:

-(qsoln + qcal) and the heat gained or lost by the reaction in units of joules.

In a calorimetry experiment, 50.0 mL each of two dilute aqueous solutions are combined and produce an extrapolated T = 22.4˚C. If the density of each solution is assumed to be equal to that of water (at 20˚C, d = 0.9982 g/mL), and the specific heat of the solution is also equal to that of water (4.186 J/g˚C), the value of qrxn would be:

-9.36 kJ

sig figs- 2.633 is measured to the?

-nearest thousandth

heat of reaction from heat of solution and heat of calorimeter

-sum of the heats=qsoln the heat lost (-)=-heat gained+ qsoln=-lqsoln+qcalorimeterl

Equipment -volumetric vs graduated -erlenmyer flask? -burette vs pippete

-volumentric-one volume -graduate-measurable volume -ehrlenmyer=pyramid -burette-workes with gravity while pipette-sucks up and pushes out -

A Beer's law calibration curve for a particular analyte has a best-fit equation of A=(11765 M-1)C + 0.197, with an R2 value of 0.9373. If a sample solution has an absorbance reading of 0.624, the concentration of the unknown sample would be:

0.0363 mM

Chemical Safety- -1-label -2-spill -3-acid or water Bunsen Burner Safety- -1-step one? -2-flame goes out? smell gass? -3-chipped glass? -4-how to heat flammable chemicals? Thermometer safety -1-shake it? -2-temp range -3-choosing a thermo? Behavior -1-eating, drinking, makeup? -2-how to read a burette higher than you -3-belongings -4-small fire-->big fire-->dropped the ball size fire

1- Read the three most important things twice: conc., hazard warning, full name 2-report spill, allow teacher to clean it 3-acid to water always ---- 1-check line for cracks 2-turn off gas 3-no it could break under heat 4-NOT A BUNSEN BURNER use a steam bath under the hood ---- 1-no... 2-(-20-100˚C) 3-know range of experiment and thermo 4- 1-no 2-lower it /use a step stool 3-away away away 4-cover with lid-->teacher-->fire dept and notify what chemicals

Experiment 4 -what was mixed in this exp?(what were products also)

1-Ba(OH)2+H2SO4-->BaSO4(s) +h2O (barium hydroxide +sulfuric acid)

List the correct procedure for lighting and working with a Bunsen burner.

1. Make sure all loose clothing and hair have been properly restrained and will not contact the flame accidentally. 2. Prepare the workspace to be sure no flammable materials are in the vicinity of the open flame 3. Inspect the tubing to the gas valve to be sure it does not have any cracks or holes that would allow a gas to leak. 4. Inspect the burner to be sure that the air intake and fuel valves work properly and can be adjusted. 5. With the sparker in hand, turn on the gas and light the flame as soon as possible to minimize unburned gas in the air. 6. Adjust the fuel valve to set the height of the flame and adjust the air intake valve to adjust the temperature (color) of the flame according to the instructions in the lab manual. 7. Monitor the flame and all nearby materials closely until the experiment is complete. Never leave an open flame unattended. 8. Shut off the burner and gas valve as soon as experimental work is completed, or anytime you must leave the flame unattended.

List the steps you would take if you find broken glassware in your lab drawer, or if a piece of glassware breaks during the lab.

1. Notify your TA. 2. Use a pair of leather gloves found in the lab to prevent nicks or cuts. 3. Clean up large pieces and dispose of the designated glass only waste container. 4. Use the dustpan and brush to sweep up small shards and dispose of them in the designated glass waste.

List the basic order of steps for beginning any experimental procedures.

1. Take any personal safety precautions that are warranted. 2. Prepare your workspace. 3. Inspect your equipment to make sure it is functioning properly.

Possible chemical reactions in aqueous media

1. precipitation (forms a precipitate) 2. acid-base (water + salt, observed through litmus test) 3. complexation (usually a color change) 4. gas-forming

Using the graph shown from an experiment measuring the density of water, what would be the correct value, units, and significance of the intercept of the regression line? Select one: A. -8.92 x 10-4 g mL-1 oC-1 represents the change in density as temperature increases. B. 1.034 g/mL represents the density at a temperature of 0oC. C. 1.034 g mL-1 oC-1 represents the change in volume as temperature increases. D. -8.918 x 10-4 g mL-1 oC-1 represents the change in volume as temperature increases.

1.034 g/mL represents the density at a temperature of 0oC.

Balmer Formula

1/wavelength= R(1/4 - 1/n(initial)^2)

Rydberg Equation (for wavelength)

1/λ = R(1/n₁² - 1/n₂²) R is 1.097*10^7 n₁ is the final energy level n₂ is the initial energy level

CV equation

100 * (standard deviation) / mean

If the balanced equation for the reaction of calcium carbonate with hydrochloric acid is: 2 HCl (aq) + CaCO3 (s) —► CaCl2 (aq) + CO2 (g) + H2O (l) How many moles of HCl can be neutralized by an antacid containing 1000 mg (1.000x103 mg) of calcium carbonate? (CaCO3 MW = 100.1 g/mol)

1000mg CaCO3 * 1g/1000mg * 1 mol/100.1 g * 2 mol HCl/1 mole CaCO3 =0.01998 mol HCl

Using the graph provided, for the reaction of 3.50 g of sodium bicarbonate with 300 mL of 0.5 M citric acid, the value of ΔT/mol (°C/mol) would be: (NOTE: molar mass of sodium bicarbonate is 84.007.) Select one: A. 2.57 °C/mol B. 2.29 °C/mol C. 216 °C/mol D. 192 °C/mol E. None of these.

216 °C/mol

In a conductivity titration, 15.00 mL of 3.00 x 10-3 M Ba(OH)2 is titrated by a 1.35 x 10-3 M H2SO4 solution. Given the reaction equation Ba(OH)2 + H2SO4 —► 2 H2O + BaSO4, the end point of the titration would be expected at a volume of:

15 * 3E-3 = 1.35E-3*x =33.3 mL

Experiment 2 vocab 1-solution 2-bond formation 3-dissolution

1homogenous, *can be solid, liquid, or gas* 2-*bonds*-solution is the medium that brings reactants close enough together to allow bonds to form; bonds breaking takes energy and bond forming releases energy 3-making the solute dissolve

When calculating the displacement volume of the thermometer, the volume reading on the buret is 29.37 mL without the thermometer, and 28.72 mL with the thermometer in place. How many significant figures should be recorded for the displacement volume of the thermometer?

The equation that is correctly balanced and shows the reaction primarily responsible for the rocket propulsion in Experiment 5 is:

2 H2 (g) + O2 (g) 2 H2O (g)

The following equations represent reactions used in Experiment 5. Of these reactions, choose the correctly balanced oxidation-reduction reaction. Select one: A. 2 HCl (aq) + Zn (s) → H2 (g) + ZnCl2 (aq) B. None of these is correct. C. 2 H2O2 (aq) →catalase→ 2 H2O (l) + O2 (g) D. H2 (g) + O2 (g) → H2O (g) E. H2 (g) + 2 O2 (g) → 2 H2O (g) F. 2 H2O2 (aq) + catalase → 2 H2O (l) + O2 (g) G. H2O2 (aq) →catalase→ H2O (l) + 2 O2 (g) H. HCl (aq) + 2 Zn (s) → H2 (g) + ZnCl2 (aq)

2 HCl (aq) + Zn (s) → H2 (g) + ZnCl2 (aq)

The volume marking at the sealed bottom of a buret segment is 48.60 mL, and has markings for every 0.1 mL. When water is added, the bottom of the meniscus sits about halfway between the line for 28.3 mL and the next mark up. What volume of water is contained in the buret segment?

20.35 mL

A 0.198-g sample of parsley is pyrolyzed and diluted with 8.00 mL of 1.0 M HCl. A 0.1-g crystal of NaSCN is added to the solution. The concentration of the prepared solution is determined to be 0.0965 mM in [FeSCN]2+. Based on this result, what is the mass of Fe in a 100-g sample of parsley

21.8 mg Fe

According to the stoichiometry of the exothermic reaction equation 2 H2(g) + O2(g) →2 H2O(g), the maximum energy that can be released by this reaction would occur at a H2:O2 ratio of Select one: a. 2:3 b. The answer cannot be determined from the information given. c. 1:2 d. 3:2 e. 1:1 f. 2:1

2:1

What were the major reaction equations for this experiment? Were there any constraints or experimental factors governing the choice and amounts of reactants and products in this reaction?

2H202 --> 2H20 + O2 <- decmposition to get oxygen Zn+ HCl --> ZnCl2 + H2<- get hydrogen H2+O2 --> H20 <- combustion to shoot off rocket mole ratio, density, order of addition

Decomposition

2H2O2-->2H2O + O2 hydrogen peroxide breaks down into water and oxygen

In a conductivity titration, 10.15 mL of 4.95 x 10-3 M Ba(OH)2 is titrated by 12.11 mL of a H2SO4 solution. Given the end point volume of titrant, what is the concentration of the H2SO4 solution? Select one: A. 5.91 x 10-3 M B. 2.07 M C. 8.30 x 10-3 M D. 4.15 x 10-3 M

4.15 x 10-3 M

The volume marking at the bottom of a buret segment is 28.00 mL, and has markings for every 0.1 mL. When water is added, the bottom of the meniscus sits about halfway between the line for 22.2 mL and the next mark up. What volume of water is contained in the buret segment?

5.85mL

Given the Rydberg equation: ΔE = RH (1/(nf2)- 1/(ni2)) In the Balmer series for hydrogen, what is the initial energy level (ni) for a photon with a wavelength of 410.2 nm? REMEMBER: h = 6.626 x 10-34 J⋅s; c = 2.998 x 108 m/s; RH = 2.18 x 10-18 J

The tablet containing _______________(answer a or b), should neutralize more acid because __________________(answers c-h). Select all correct answers. CaCO3 MW = 100.1 g/mol Mg(OH)2 MW = 58.32 g/mol CaCO3 + 2 HCl —► CaCl2 + H2O + CO2 Mg(OH)2 + 2 HCl —► MgCl2 + 2 H2O

750 mg Calcium Carbonate There are more moles of Base ?

In a calorimetry experiment, 50.0 mL each of two dilute aqueous solutions are combined and produce an extrapolated ΔT = -22.4˚C. If the density of each solution is assumed to be equal to that of water (at 20˚C, d = 0.9982 g/mL), and the specific heat of the solution is also equal to that of water (4.186 J/g˚C), the value of qrxn would be:

9.36 kJ

Mean

=(sum of the measured values) / (the number of measurements)

Absorbance

=-log(I/I₀) light intensity of the sample/light intensity for the blank solution. A measurement that has no units.

Corrected Volume

=V(water originally)-V(displacement=Vfinal-Vinitial)-V(volume at final temp. recording)

Density

=mass/volume (g/mL)

Molarity

=moles of solute/total liters of solution

Degrees of Freedom

=number of observations - 1 (n-1)

Standard Deviation

=square root((sum of the squares of the deviation from the mean)/number of observations - 1)

Heat of reaction

=the sum of (the heat of formation of the products) - the sum of (the heat of formation of the reactants)

Combination reaction

A + B --> C A reaction in which two or more substances combine to form a single substance.

A conductivity plot for the titration of barium hydroxide with sulfuric acid is shown below. Assuming sulfuric acid is the titrant, which ion species would you expect to be significant in solution when 8.62 mL of titrant had been added? Select one: A. Ba2+ B. SO42- C. H+ D. OH- E. A, B, and D. F. B and C only. G. A and D only. H. None of these

A and D only.

Tare

A button on the analytical balance to bring the reading to zero.

Purpose of the calibration curve

A calibration curve can be used to predict concentration based on absorbance based on the linear relationship between the two that is defined by Beer's law. OR To define the relationship between Allura Red AC concentration and absorbance.

Combustion reaction

A compound and an oxidant are combined to form heat and another product. Combustion reactions between hydrocarbons and oxygen form water and carbon dioxide.

Calorimeter

A container that has a suitable liquid that makes good thermal contact with the process under investigation (usually water).

Graduated Cylinder

A cylindrical tube with volume marks along the side.

After you finish the Beer's Law experiment, you notice a dark smudge on your cuvette you used to blank. How would you expect this to have affected your results for absorbance values after the blank?

A dark smudge would affect the passing of light through the cuvet and would provide inaccurate absorbance values.

Rubber bulb

A device used to aid in drawing a solution into a pipet.

State function

A function that is independent of the path that a reaction follows to move from reactant to product.

Electric discharge tube

A glass tube that contains metal electrodes at each end and is filled wiht a low pressure gas, such as hydrogen, helium or mercury and a high voltage is placed across the electrodes and when the current is switched on a stream of fast moving electrons shoot through the gas from the cathode to the anode.

Buret

A glass tube with uniform diameter that is mounted vertically and has a stopcock at its lower end to regulate the liquid flow.

Intensive property

A physical property that doesn't depend on the amount of sample.

Beer's Law Plot

A plot of Absorbance vs. solution molarity

Endothermic reaction

A reaction that absorbs heat energy from the surroundings

Gas-forming

A reaction that produces an insoluble gas such as: hydrogen gas, carbon dioxide, sulfur dioxide, hydrogen sulfide, or ammonia.

Exothermic reaction

A reaction that releases heat energy into the surroundings

redox reaction

A reaction where there is either a transfer of electrons or a change in the oxidation numbers of the substances taking pat in the reaction.

A. 7.85 B. 7.30 C. 8.45 (Correct)

Oxidation

A second provides those electrons and therefore has a more positive charge in the products.

Cuvette

A small plastic solution cell placed in the colorimeter.

Precipitate

A solid that forms from a solution during a chemical reaction.

Continuous emission spectra

A spectrum with some many emitted frequencies of radiation that the lines overlap and the light looks like a rainbow.

In calorimetry, the enthalpy change of the reaction, qrxn, is defined to be: (Select all that apply.)

A. -(qsoln + qcal) B. qcal -qsoln C. qsoln -qcal D. ΔH / nreagent E. the heat gained or lost by the reaction in units of joules. F. the heat gained or lost by the reaction in units of joules/mol. G. the difference between the extrapolated maxiumum temperature and the initial temperature in a reaction. H. qsoln + qcal I. Both A and E are true. (Correct) J. Both D and F are true.

For the reaction of 3.5 g of sodium bicarbonate with 30 mL of 0.5 M HCl if the temperature rises from 22.4°C to 32.1°C. The value of ΔT/mol (°C/mol) would be:

A. 0.361 °C/mol B. 2.77 °C/mol C. 233 °C/mol (Correct) D. 0.00430 °C/mol

Given the Rydberg equation: ΔE = RH (1/(nf2)- 1/(ni2)) In the Balmer series for hydrogen, what is the initial energy level (ni) for a photon with a wavelength of 434.1 nm? REMEMBER: h = 6.626 x 10-34 J⋅s; c = 2.998 x 108 m/s; RH = 2.18 x 10-18 J

A. 1 B. 2 C. 3 D. 4 E. 5 (Correct) F. 6

The following equations represent reactions used in Experiment 5. Of these reactions, choose the correctly balanced catalytic reaction.

A. 2 HCl (aq) + 2 Zn (s) → H2 (g) + ZnCl2 (aq) B. H2 (g) + O2 (g) → H2O (g) C. None of these is correct. D. 2 H2 (g) + O2 (g) → 2 H2O (g) E. 2 HCl (aq) + Zn (s) → H2 (g) + ZnCl2 (aq) F. 2 H2O2 (aq) →catalase→ 2 H2O (l) + O2 (g) (Correct) G. 2 H2O2 (aq) + catalase → 2 H2O (l) + O2 (g)

For the reaction of 3.5 g of sodium bicarbonate with 30 mL of 0.5 M HCl if the temperature rises from 22.4°C to 32.1°C. The value of ΔT/mol (°C/mol) would be: A. 233 °C/mol B. 0.361 °C/mol C. 2.77 °C/mol D. 0.00430 °C/mol

A. 233 °C/mol

A. 28.35 mL B. 20.35 mL (Correct) C. 28.25 mL D. 20.25 mL

A. 4 B. 3 C. 2 (Correct) D. 1

In a conductivity titration, 10.15 mL of 4.95 x 10-3 M Ba(OH)2 is titrated by a 4.15 x 10-3 M H2SO4 solution. The end point of the titration would be expected at a volume of:

A. 6.053 mL B. 0.002024 mL C. 10.15 mL D. 12.11 mL (Correct)

A. 7.53 mg (Correct) B. 0.615 mg C. 7.53 g D. 615 mg E. None of these. F. 2.15 mg

The molecular equation for the reaction in Experiment 4 is: Ba(OH)2 + H2SO4 →BaSO4 + 2 H2O Which of the following statements correctly indicates which species are conductive?

A. Barium hydroxide is a soluble ionic substance that is highly conductive in solution, and sulfuric acid is a strong acid that also conducts strongly in solution. In contrast, barium sulfate is an ionic solid, and, as a solid, it is nonconductive. Water is a covalent substance that is also a nonconductor. (Correct)

The molecular equation of a reaction is NaHCO3 (aq) + HCl (aq) →NaCl (aq) + H2O (l) + CO2 (g). Both the initial solutions and the final solution were transparent and colorless, but bubbles were seen during the reaction. Based on this equation and the observations of the reaction, the spectator ions in the ionic equation would be:

A. Na+ B. Cl- C. H+ D. CO2 E. H2O F. Two of the above (Correct) G. Three of the above H. None of the above

Based on your observations in Experiment 5, an exothermic reaction may be identified via observation in the lab when it: (select all correct answers)

A. Produces bubbles. B. Two of these (Correct) C. Three of these D. Dissolves a solid reactant. E. Causes a loud popping noise. F. Grows cold. G. Forms a precipitate. H. Causes water condensation farther downstream

The temperature at the start of a reaction was 22.8°C and the final temperature was 32.9°C. Based on these observations, the reaction of sodium bicarbonate with hydrochloric acid would be:

A. endothermic, because energy is transferred from the reaction to the surroundings. B. exothermic, because energy is transferred to the reaction from the surroundings. C. exothermic, because energy is transferred from the reaction to the surroundings. (Correct) D. endothermic, because energy is transferred to the reaction from the surroundings.

A. gas-forming (Partially Correct) B. none of the above C. two of the above (Correct) D. acid-base E. complexation F. precipitation

During the second trial of the neutralization of the crushed antacid tablet by an excess of HCl, a student notices that the pH of the solution has not increased. The first trial ran as expected. The student should check the following probable issues to be sure the experiment is set up correctly: A. The powdered tablet is immersed in the solution. B.The pH probe is correctly calibrated. C. The tablet contains too little base. Incorrect D. The tablet contains too much base.

A. the powdered tablet is immersed in the solution

Define the variables in Beer's Law

A: (no units), absorption, the intensity of light passing through the sample relative to the intensity of light passing through the blank (l0 = -log(l/l0) ε: (1/M*cm), molar extinction coefficient/ molar absorptivity, describes how strongly the analyte absorbs light at a particular wavelength ι: (cm), the path length of light through the solution contained in the cuvet C: (M), the concentration of the analyte in solution

How are transmittance and absorbance related (verbally and mathematically)? Using observations of a solution in a cuvette, can you predict which would have high transmittance and which would have low? For absorbance?

A= 2-log(%t) As % T increases, abosrbance - You can tell the transmittance by the darkness of the cuvette

Beer's Law

A=xbc

Beer's law

A=εlc A: absorbance (no units) ε: molar extinction coefficient *defines how strongly the analyte absorbs at a particular wavelength* (M^-1cm^-1) c: concentration of the analyte in solution (M) l: path length (1 cm)

What is your BEST resource for understanding the nature of the chemical hazards of materials you work with in lab?

Safety Data Sheets

Equations for Experiment 7: Beer's Law

Absorbance = (Molar absorptivity e) * (the path of light l) * (Concentration of analyte C)

Transmittance equation

Absorbance = -log(I/I₀) I/I₀ is radiance

Beer's law -formula -variable defintions

Absorbance=εbc -An eggs, bacon, and cheese with beer please -Absorbance=-log(Intensity of sample/intensity of blank solution) which also =*2-log(base 10)(T%) * -ε-molar extinction coeff constant (how strongly it absorbs light) -b-path length (cuvette) -c-concentration

Does calibration using standards help to improve the precision or accuracy of the experiment?

Accuracy. Calibration defines the accuracy and quality of measurements recorded using a piece of equipment.

What types of samples were used in this experiment? What made these samples particularly well suited to this experiment? What precautions had to be taken?

Acid and antacid or base. Antacid neutralizes the acid like stomach acid. Had to be careful around acid

Should you add acid to water, or water to acid?

Acid to water. If you add water to acid, you form an extremely concentrated solution of acid initially and the solution may boil very violently, splashing concentrated acid. If you add acid to water, the solution that forms is very dilute and the small amount of heat released is not enough to vaporize and spatter it.

Acid Base Reaction

Also called a neutralization reaction. When an acid and a base combine to form water and a salt.

When the procedure calls for making a more dilute solution of an acid, or mixing an acid with other solutions, what is the correct order of steps?

Always Add Acid - Either add all of the water or non-acid component first, or add a significant portion, before adding the acid to the mixture. This helps to minimize the heat generated, which could otherwise create dangerous fumes or reactions.

Acids and water (for dilution

Always add acid! Not the other way around or it makes a bunch of heat

PPE

Always wear googles, wear gloves except when leaving the lab and working with electronics/labtop

Acid-base

An acid and a base react to produce water and a salt.

Define random error and give examples.

An error that arises from uncontrolled, and often times uncontrollable, variables in an experiment which has equal chance of being positive and negative. This type of error cannot be detected or corrected for. Reading volume on a flask from a different angle each time. Mass measurements can be affected as water enters or leaves the specimen being measured. Estimations between the lines may be incorrect. Affects the precision of results*

Define systematic error and give examples.

An error that occurs due to a flaw in the experimental design or in the equipment. These types of errors can be detected and corrected. Water in a heated beaker evaporating. Air pressure not being 1 atm. Incorrectly tared balance A person consistently takes an incorrect measurement. An instrument is worn out and measurements are difficult to read. Not reading the meniscus of a liquid at eye level. Affects the accuracy of results*

Colorimeter

An instrument used to detect the transmittance of light through a solution.

Colorimetry

An instrumental method based on the measurement of light absorption by colored solutions and is widely used for performing chemical analyses.

Atomic emission spectrum

Analysis of light from an atom by means of a spectroscope

Experiment 4

Aqueous Reactions: To learn methods for collecting data in different types of experiments and to investigate some types of reactions which occur in aqueous solutions.

Conductometric Titration of Barium Hydroxide and Sulfuric acid

As the number of ions in the solution decreases, the conductivity decreases.

How many times should you read the label on a reagent container and compare it with the lab manual?

At least twice each time you remove material from the container.

Apparel

Attire: long well fitting cotton or wool clothing; closed leather shoes, no jewelry, no make up application, no contacts

The molecular equation for the reaction in Experiment 4 is: Ba(OH)2 + H2SO4 →BaSO4 + 2 H2O How is conductivity reflected in the net ionic equation? Select one: A. Barium hydroxide and barium sulfate are soluble ionic substances that will ionize in solution and be conductive, but sulfuric acid is a covalent molecule that is nonconductive, as is water. Therefore, barium ions are the only spectator ions and will not appear in the net ionic equation. B. In this experiment, barium hydroxide and barium sulfate are soluble ionic substances that will ionize in solution and be conductive. Sulfuric acid is a strong acid that ionizes in solution and is conductive. Water is a covalent substance and is nonconductive. Thus, barium ions and sulfate ions will be spectator ions and will not appear in the net ionic equation. C. Barium hydroxide is a soluble ionic substance that is highly conductive in solution, and sulfuric acid is a strong acid that also conducts strongly in solution. In contrast, barium sulfate is an ionic solid, and, as a solid, it is nonconductive. Water is a covalent substance that is also a nonconductor. Therefore, the net ionic equation will have no spectator ions, and only the reactants will be written as ions in solution. D. Barium hydroxide and barium sulfate are both ionic solids that are nonconductive, and water is a covalent substance that is nonconductive, but sulfuric acid is a strong acid that is highly conductive in solution. Therefore, there are no spectator ions and the net ionic equation will have H+ and SO42- ions on the reactant side.

Barium hydroxide is a soluble ionic substance that is highly conductive in solution, and sulfuric acid is a strong acid that also conducts strongly in solution. In contrast, barium sulfate is an ionic solid, and, as a solid, it is nonconductive. Water is a covalent substance that is also a nonconductor. Therefore, the net ionic equation will have no spectator ions, and only the reactants will be written as ions in solution.

Conclusion for Experiment 5: Rockets

Based on the experimental data, the order of gas addition did not have a strong effect on the distance traveled by the pipette bulb.

Why was the blue wavelength of the colorimeter used for this experiment? Why might you choose a different setting in a new analysis for a different chemical species?

Because we were experimenting with a red color, blue is on the opposite side of the color spectrum so red absorbs blue light. Red solution absorbs light in the violet or blue spectrum.

Experiment 7

Beer's Law: To introduce Beer's Law relating solution concentration to absorbance, to use the measurement of light absorption to detect the colorimetric reaction of thiocynate with iron and to determine the iron content in food samples.

Effect of a dark smudge on calibration curve

The effect of a dark smudge would be a significant increase in the calibration measurement of absorbance, and subsequent samples in comparison would have much less absorbance than they would have against a true blank.

Understand the implications of balanced reactions and predict which species exist at different times in a reactions progress.

Before the titration the solution of Barium Hydroxide is basic. During the titraiton the solution slowly becomes more neutral and then past the level of titration it will become acidic due to too much acid. The ions are less free floating as it becomes titrated and once all the base has been reacted the conductivity will increase again due to floating ions.

What is the purpose of a blank in Beer's Law experiment?

Blank is used to measure the absorbance in the cuvet

Bond formation (exothermic or endothermic)

Bond formation releases energy because the potential energy is lower than the separate states (it is more stable, more favorable). We would expect these reactions to be exothermic.

In calorimetry, the enthalpy change of the reaction, qrxn, is defined to be: (Select all that apply.) Select one: A. -(qsoln + qcal) B. qcal -qsoln C. qsoln -qcal D. ΔH / nreagent E. the heat gained or lost by the reaction in units of joules. F. the heat gained or lost by the reaction in units of joules/mol. G. the difference between the extrapolated maxiumum temperature and the initial temperature in a reaction. H. qsoln + qcal I. Both A and E are true. J. Both D and F are true.

Both A and E are true.

The use of a conductivity meter was especially useful for this experiment because

Both reactants are highly conductive, while neither product conducts at all, making the end point of the titration easy to identify.

In the reaction KOH(s) + HBr (aq) → KBr(aq) + H2O(l), the spectator ion(s) would be: (select all that apply.) Select one or more: A. HBr B. KOH C. OH- D. H+ E. Br- F. H2O G. K+ H. There are no spectator ions in this reaction. I. KBr

Br-

Procedures for Experiment 5: Gas Forming Reactions and Rockets

Build the gas-generating apparatus. Mix the hydrogen peroxide with yeast in the apparatus test tube and collect the oxygen gas produced in the water-filled pipette bulb on the apparatus. Mix the zinc and hydrochloric acid in the apparatus test tubes and collect the hydrogen gas produced in the water-filled pipette bulb on the apparatus. Record how much oxygen gas and hydrogen gas were produced and the ratios used in the pipette bulb that will be launched. Take the pipette bulb to the TA to ignite the gases and record all observations about the launch.

What experimental components hindered the launch of the rocket in Experiment 5?

Capped the bulb with a gloved finger only, excess water on the bulb prevented full combustion

Electron moves from ground state to an excited state (n=5)

The electron absorbs energy to move up in energy state (excitation) and therefore gains energy (positive), putting it further from the nucleus in a less stable state.

C. 0.0472 mM

CV formula

CV = (Std Dev)/(Mean)*100% CV is used to compare the standard deviations of two different samples

Bohr model

The electron orbiting the proton in a hydrogen atom can only exist in certain orbital states labeled with a quantum number n.

To carry out a calorimetry experiment quantitatively, what is necessary?

Calculations must be made in moles rather than grams. The thermometer must be calibrated to give accurate temperature readings in Celsius. The calorimeter must be calibrated to account for heat loss of the system. All solutions must be equilibrated to room temperature before beginning the experiment.

Experiment 3

Calibrate pH.one run with whole antacid tablet and another three runs with crushed tablet. Create chart of pH vs. Time

Procedures for Experiment 8: Spectroscopy

Calibrate the spectroscope. Use the spectroscope to record the spectral characteristics of three sources of light. Use the spectroscope and spectrometer to determine the line and emission spectra of hydrogen gas. Use the spectroscope to observe the spectral characteristics of different metals. Identify an unknown metal from the previously observed spectral characteristics of different metals.

Imperfect insulation with caloriometers

Calorimeters will still allow for some heat transfer between the experiment and the environment. We take into account this amount lost to the environment by finding the calorimeter constant and estimating the heat lost to the environment (calibrating).

A technique in which the temperature change in a closed system is measured to assess the heat transfer between a reaction and its surroundings is called

Calorimetry

Explain the difference between a stoichiometric reaction and a catalytic reaction. Give one example for each that was not a part of the experiment, and be specific with a type (redox, combustion, or acid-base reaction).

Catalytic reaction: lower activation energy than the corresponding uncatalyzed reaction, resulting in a higher reaction rate at the same temperature for the same reactant concentrations. Example: Potassium permanganate as a catalyst for the decomposition of hydrogen peroxide. Redox reaction. Stoichiometric reaction: quantities of the reactants and products show that all of the reactants are consumed and none remain after the end of a chemical reaction. Example: Ethane combusts in the presence of oxygen to form water and carbon dioxide.

Based on your observations in Experiment 5, an exothermic reaction may be identified via observation in the lab when it:

Causes a loud popping noise and/or produces bubbles

Systematic error

determinate error- can in principle be discovered and corrected. (balance has been calibrated incorrectly and constantly reads 2.3 g heavier than the material being weighed. *represents a limitation to accuracy of a measurement.

Balmer Energy Formula

Change in energy = Rh(1/(n final)^2)-1/(n initial)^2)

The temperature at the start of a reaction was 26.5°C and at the end of the reaction was 18.5°C. Based on these observations the reaction of sodium bicarbonate with citric acid would be:

endothermic, because energy is transferred to the reaction from the surroundings.

In the reaction NaOH(s) + HCl (aq) → NaCl(aq) + H2O(l), the spectator ion(s) would be:

Cl-

In the reaction NaOH(s) + HCl (aq) → NaCl(aq) + H2O(l), the spectator ion(s) would be: (select all that apply.)

Cl-

Potential source(s) of error in Experiment 5 include: (select all correct answers)

Collecting water vapor in the pipette bulb The presence of liquid water in the pipette bulb Losing H2 gas because it is less dense than air

Procedures for Experiment 4: Conductometric Titrations

Combine barium hydroxide and water and record conductivity with probe. Calculate predicted volume of titrant and add titrant to approach predicted volume. Record conductivity while adding more titrant to determine a minimum conductivity. Repeat process for a total of three trials.

molarity

Concentration in mol/L of solution

Experiment 4

Conductivity vs. Volume. Conductivity measurements will reach a minimum then increase again signaling you're past the titration. Use the moles at end point to determine stoichiometric values.

Experiment 5

Conductometric Titration: To introduce conductivity as a means to follow a chemical reaction from soluble reactants to insoluble products and to apply the Law of Conservation of Matter to balance a chemical equation.

How does one use an experimentally-measured enthalpy change to determine the standard molar enthalpy of a reaction?

Convert grams to moles of reactants and then divide heat of reaction by moles. kj/mols

Precipitation

Creates solid precipitate

In a determination of the mass of Allura Red AC in one serving of a food sample, the result is found to be ~10% too low when compared with another determination. The most likely experimental error to explain this result would be:

D. When the 1 x 10-5 M stock standard was prepared, instead of transferring 500 microliters of the 2 x 10-3M stock to the 10.00-mL volumetric flask, the experimenter transferred 550 microliters. This increased the slope of the calibration line by 10%, causing the sample solution concentration to be calculated 10% too low.

Density, vol, temp relationship

D=m/v PV=nRt therefore D=m/(kT) Inversely proportional at constant pressure

If a flammable substance in a beaker should catch fire while you are working but the flames are relatively contained, what should you do to extinguish the flame? What should you not do?

DO: Use the chemical fire extinguisher from the lab. Pull the pin, aim the nozzle to the beaker, and pull the lever. DO (Best, simplest): Turn off the heat source immediately and use a watch glass to cover the beaker. DON'T: Use water from the nearest sink to douse the flame.

Determining delta T

DT=T(final)-T(initial) If positive, endothermic If negative, exothermic

Experiment 1

Data Studio and Excel Tutorial: Basic information on data studio.

Conclusion for Experiment 2: Aqueous Reactions

Decrease in temperature of the surrounding water meant the reaction was endothermic, and vice versa. Calorimetry can be used to determine if reactions are endothermic or exothermic. From this experiment, I learned that in each reaction, even if the same processes are occurring (dissolving, disassociating, gas-forming), the concept of exothermic and endothermic reactions are separate concepts.

Hess's Law

Delta H of reaction = (Sum of delta h for products) - (sum of delta h for reactants)

How are dependent and independent variables defined?

Dependent- Volume (responding to change) Independent-Temperature (What's being changed)

Experiment 2

Determined maximum and minimum temperatures reached. Proved which were endothermic(temp decreased) and which were exothermic(temp increased).

How did we control for the variables in this experiment to make a sound determination and comparison to reference data?

Determined the percent error from slopes of the literature data and the experimental data. we also got slopes from three other groups of experimental data

Thermochem- --First Law of Thermo --Standard unit of measurement for Thermochemistry --Change in heat of reaction --differentiate standard enthalpy change and enthalpy change ---h of formation

Energy is never created or destroyed Joules(J)-heat energy enthalpy change -standard=standard conditions 1atm and 298˚K -formation=change in enthalpy of the creation of a molecule from its constituent elements in their standard states

Relationship b/w pressure and temperature

Direct

Reminders for Question 16 when calculating density

Do not use volume readings with the probe. Use only initials

Blank

Does not contain analyte

Would you expect a bond forming reaction to be endo- or exothermic?

exothermic

Rydberg Equation (for energy)

E= Rhc(1/n₁² - 1/n₂²)

Fundamental light equations

E=hv c=λv E=energy in joules h=Planck's constant (6.626*10^-34) v=frequency (s^-1) c=speed of light (2.998*10^8 m/s) λ=wavelength (m)

For endothermic reactions, will the final temperature be higher or lower? For exothermic reactions, will the final temperature be higher or lower?

ENDOTHERMIC: higher EXOTHERMIC: lower

How does the Hydrogen lamp produce light? How is this relevant to the purpose of this experiment? What color is the Hydrogen lamp to the naked eye? What appears when observed through a spectroscope?

Electrical discharge tube-glass tube that contains metal electrodes at each end and is filled with a low-pressure gas, such as hydrogen, helium, or mercury. A stream of fast moving electrons shoots through the gas from the cathode. These electrons get excited to a new energy level and then return to their ground state resulting in the emission of light.

Wave theory

Electromagnetic radiation is a form of energy consisting of oscillating electric and magnetic fields that move the direction of propagation at the speed of light.

Net Ionic Equation

Eliminate spectator ions= molecular: Ag+ + NO3- + H+ +Cl- --> AgCl(s) + H+ +NO3- Net ionic: Ag+ + Cl- --> AgCl(s)

Why is enthalpy change considered a state function? How does this relate to Hess's Law?

Enthalpy change is considered a state function because it is only dependent on two thermodynamic state properties (like temperature and pressure) of the state of the substance at the moment of change in enthalpy. The path required to reach these states has no effect on enthalpy change.

Random error

Error arises from uncontrolled, and uncontrollable variables in an experiment that could be equally either positive or negative CANNOT be detected or corrected Ex. Human error, measuring uncertainty

Experimental error

Error associated with every measurement that can only at best be minimized by following proper lab technique (there are two types of this)

Systemic error

Error from a flaw from the equipment or experimental design CAN be detected or corrected Ex. Scale was calibrated wrong

The following three actions could produce a significant source of error in the results for Experiment 5: 1. Using an excess of yeast in the reaction with H2O2. 2. Using an excess of HCl in the reaction with zinc. 3. Collection both gases in the same pipet bulb.

False

F. Two of the above. (Na+ and Cl-)

In Experiment 7, the experimental purpose of creating the Beer's Law plot of absorbance vs. concentration of Allura Red AC was to prove that the relationship between the concentration of a solution and it's absorbance is linear.

False

T/F: The following three actions could produce a significant source of error in the results for Experiment 5: Using an excess of yeast in the reaction with H2O2. Using an excess of HCl in the reaction with zinc. Collection both gases in the same pipet bulb.

False

Procedures for Experiment 1: Mass, Volume, and Density

Fill buret with assigned water sample and clamp it to a beaker on a hot plate. Heat the water after noting initial temperature of the water. Turn off hotplate upon reaching 80 degrees C and remove beaker. Record temperature values upon seeing a change in volume. Goal: Compare densities of different types of water (purified, distilled, contaminated)

Calculating endpoints

Find the equations of the titration, and extrapolate and find their intersection. Their intersection is the endpoint of the titration

Balmer Series

Four wavelengths of light emitted by hydrogen that follow a specific formula

Behavior of photon

From class, photons behave both in a wave-like manner as well as acting like particles.

If you need to work with a flammable or volatile solvent, which piece of lab equipment should you be sure to use?

Fume hood with good ventilation.

When should you inspect the glassware in your drawer for chips, cracks, or chemical residues?

Glassware should be inspected during an experiment (before using any glassware), before beginning an experiment, and during check-in (where any glassware can be replaced for free) in order to prevent injuries, accidents, or unwanted complications.

Na and Cl

Precision and Accuracy

Great precision does not imply greater accuracy

Based on your observations in Experiment 5, an exothermic reaction may be identified via observation in the lab when it:

Grows warm, Causes a loud popping sound

Catalytic reaction

Has catalyst Redox Catalyst: 2CO(g) + O2(g) --(Pt)--> 2CO2(g)

Experiment 1

Heat buret segment of water and measure volume to get a denisty vs. Temperature graph

Was yeast the catalyst?

Heck no. yeast produces the catalyst called catalase

Enthalpy and Hess's law relation

Hess's Law states that the enthalpy change is the sum of all changes, so it doesn't matter which order the changes were in.

Temperature's effect on density of a solution

Higher temperature, lower density and vice versa

Accuracy

How close a measurement is to the true value

Define precision.

How closely obtained/measured values agree with each other.

Define accuracy.

How closely obtained/measured values agree with the "true" value.

Solubility

How easily the solvent can dissolve a solute (the concentration of solute in a saturated solution at a specified temperature)

Final temperature with endo/exothermic reactions

IF measuring temperature of the surroundings (i.e. solution) Exothermic - higher Endothermic - lower

Why ice floats

Ice is less dense than water

Why does ice float in water?

Ice is less dense than water.

Hess's Law.

If a reaction can be written as the sum of two or more other reactions, the change in heat for the overall process must be the sum of the change in H values of the constitute reactions.

Hess's Law

If a reaction is teh sum of two or more other reactions, the change in enthalpy for the overall process must be the sum of the change in enthalpy values of the constituent reactions.

For the most accurate determination, the absorbance of the samples should fall in the middle of your calibrated range (~0.5-0.7 absorbance units). What will you do if the absorbance for your sample is greater than 1.2? Explain the process in detail, including the instruments used. Remember that you must preserve the precision to 4 significant figures.

If the absorbance for your sample is greater than 1.2, we must consult our TA to determine whether calibration standards should be prepared again or if any standard concentrations should be adjusted. Because of the relationships seen in the equation for absorbance (A=ειC), a higher absorbance would result from a higher concentration (considering ε and ι are constant). To lower the absorbance, a decrease in concentration would be required and the solution providing the higher absorbance value should be diluted. For this experiment, 501 nm wavelength gave the highest absorbance value. If it was necessary to decrease this maximum wavelength, lower concentrations should be used.

How it works

If two electrodes or conductors with a potential difference are placed in the electrolyte solution, the cations migrate to the negative electrode and the anions move to the positive, producing an electric current in the solution. (us/cm)

Calibration's purpose

Improves accuracy

What was added in exp 7 to make the Fe visible

NaSCN (sodium thiocyanate)

Conclusion of Experiment 1: Mass, Volume, and Density

In this experiment, it was determined that the density of water decreases as temperature increases. It was also determined that water samples containing more solutes, like contaminated water and purified water, have higher densities on average.

Conclusion for Experiment 7: Beer's Law

In this experiment, we put Beer's Law into practice while understanding measurements regarding concentrations and how they relate to wavelength and absorbance ranges. While comparing different concentrations of solutions, the higher concentrations had a higher absorbance value, thus proving that absorbance and concentration are directly proportional.

Experiment 6

In this lab, the temperature of three different reactions will be recorded and graphed. The graph will be used to extrapolate the maximum temperature of those reactions , and those temperatures will in turn be used to calculate their enthalpy change. Enthalpy is the total heat content of a system. Negative enthalpy changes indicate an exothermic reaction, as the heat content of the system escapes to its surroundings. Positive enthalpy changes indicate an endothermic reaction, as the heat content of a system increases due to the absorption of heat from its surroundings.

If you had a conductometric titration of barium hydroxide, but used barium hydroxide instead of sulfuric acid as titrant, what should the plot of conductivity vs. volume of titrant added look like?

Increasing steadily in conductivity, assuming that the concentration of the titrant is higher than the concentration of the analyte solution

When reading the label on a reagent container, what are the three most important pieces of information?

Name, concentration, and hazard warning(s)

Instead of adding distilled water to the barium hydroxide, the experimenter added tap water.

During a conductivity titration, 15.0 mL of Ba(OH)2 is placed in a beaker with 35 mL of H2O. At the start of the titration, the initial conductivity reading is nearly double that of a previous trial and does not decrease to zero at the minimum as expected as sulfuric acid is added, even though the minimum occurs at the expected volume. One possible explanation for these observations would be: Select one: A. Instead of adding distilled water to the barium hydroxide, the experimenter added tap water. B. The experimenter mistakenly added twice as much barium hydroxide to the beaker. C. The barium hydroxide and sulfuric acid were mistakenly combined in the beaker, and the water was used to fill the buret. D. The sulfuric acid was added to the beaker while the barium hydroxide was used to fill the buret.

Instead of adding distilled water to the barium hydroxide, the experimenter added tap water.

What causes absorption

Intensity of light passing through sample compared to the blank in the spectrometer

Density

Intensive property = mass/volume

Redox reaction

Involves a transfer of electrons between two species

When a species gets reduced

It gains electrons (OIL RIG), or adding electrons reduces the oxidation number of the species

What happens to a species when it is reduced?

It gains electrons.

Your lab partner accidentally gets a mist of your solution in her eye. You immediately help her to the eye wash to rinse it. After about a minute, she feels better and is ready to get back to work. What should you do?

Keep her in the eye wash for at least 15 minutes, and then make sure she goes to student health, just to be sure.

Based on the temperature change described in Question 4, the reaction of sodium bicarbonate with hydrochloric acid would be

exothermic, because energy is transferred from the reaction to the surroundings.

You spill some NaOH on your gloved hand and onto your arm. The wrist was exposed, and the NaOH got into direct contact with your skin. What do you do?

Let TA know and go to sink to wash your hands (at least 15 minutes) & take the glove off before you do any of that

Your lab partner accidentally spills some acid on his wrist and watchband. What should you do?

Let the TA inspect his wrist to see if it is okay. Remove the watch and wristband immediately, and rinse his wrist for at least 15 minutes to be sure all hazardous material has been washed away.

continuous light spectrum

Light source has an even range of wavelengths

discrete light spectrum

Light source only has a few strong distinct wavelengths

Why does the lab safety policy address loose clothing, dangling jewelry, and contact lenses?

Loose clothing/dangling jewelry: can impede movement, knock materials over, can present a fire hazard. Contact lenses: can hold hazardous chemicals close to the eyes. All of these items increase the risk of injury.

How to set up that really weird chart on p 52

M1V1=M2V2 M=molarity V=mass

Why 2 foam cups for the calorimeter

Mainly to help insulate the reaction so that extra heat is not lost to the environment.

Reminders for Balancing equations

Make sure both sides have the same number of atoms of each element, check carefully

What technical challenges had to be overcome? How might variables in experiment design affect the results?

Make sure the antacid is completely immersed in the solution, make sure there is enough base to neutralize the acid

How can one assess the progress of a reaction from a graph of pH vs time. Identify which points are most useful in determining pH/time

Make two different lines where the pH begins to level off. This means the acid has been neutralized.

Experiment 3

Mass, Volume and Density: To measure the density of a water at room temperature and to examine the effects of temperature on density.

Law of Conservation of Mass

Matter cannot be created nor destroyed.

Why do we only record absorbance at a wavelength that gives the greatest absorbance value for Allura Red?

Maximum wavelength = most light absorbed

Mean formula

Mean=(sum of the results)/(number of results)

Calorimetry

Measuring the amount of heat energy emitted or absorbed in some chemical process.

Experiment 2 Specifics

NH4Cl+H2O= endo Na2Co3+H2O=+T-->exo

Why use max wavelength?

Molecules all have a specific wavelength at which they absorb the most. This allows us to make easier comparisons between molecules of the same kind at different concentrations and ensures that we are comparing actual absorbance from this molecule and not background absorbance. Also, it would be impossible to compare at different / multiple wavelengths.

You want to bring a snack to the lab. When are you allowed to have it on the lab bench.

NEVER. You do not want to contaminate your food. If you have issues with your blood sugar, go eat that stuff outside

Exothermic

Negative net energy, a reaction occurs that releases energy from the reaction to the surroundings in the form of heat.

Acid-base

Neutralize, cation of acid reacts with OH to produce water and the Cation of the base reacts with the acid to produce a salt.

Stoichiometric reactions

No catalyst Ex. Combustion Stoichiometric reaction: 2H2(g) + O2(g) ---> 2H2O(g)

Rydberg constant and non-hydrogen elements

No, because mercury has many electrons with many possible final energy states to come to rest at

What is a decomposition reaction? Name on that you have learned in 101L.

One reactant yields two or more products. Decomposition of NaOH (s)

Reduction

One species in this reaction gains electrons giving it less positive charge

Random Error

One type of experimental error that arises from limitations in the ability to make physical measurements. It has an equal chance of being positive or negative. It is always present and cannot be corrected.

Systematic Error

One type of experimental error that can be discovered and corrected. It may be positive or negative and can result from faulty calibration of a measuring device.

Oxidation and Reduction

Oxidation means the atom loses electrons (increase in oxidation number) Reduction means the atom gains electrons (and reduces the oxidation number, haha)

Finding oxidation number (rules)

Oxygen is always -2 Akali metals have +1 usually Rare earth metals have +2 usually Nearly every compound will have a sum of zero for the oxidation numbers (very simplified explanation, if you need more help seek online resources)

Cause of absorption

Photons are absorbed to provide the energy that excites the electrons to the next energy level.

While weighing out a reagent for use in an experiment, a student finds he has leftover reagent. What should the student do?

Place the excess reagent in the appropriate solid or liquid waste container to prevent contamination of the stock reagent.

Procedures from Experiment 2: Aqueous Reactions

Place two Styrofoam cups inside of each other with a stir bar and distilled water inside, a lid on top, and a temperature probe inserted around the edge. Place the apparatus on a stir plate, then lift the lid, add ammonium chloride, replace the lid, and turn on the stir plate. Record the temperature at specified intervals and make observations by lifting the lid occasionally. Dispose of solution according to procedures (liquid or solid waste) and repeat this process with sodium carbonate and distilled water, sodium bicarbonate with citric acid, and hydrochloric acid with magnesium.

E=hv

Planck's Law

6.63x10^-34(Js)

Plank's Constant

Endothermic

Positive net energy, more energy is required to break the bonds of reactants tan is released by forming bonds

Calculating Precision vs Accuracy

Precision: (a measure of reproducibility compare mean and sd standard deviation square root(sum of each(measured-average)^2/df) df=n of values -1 Accuracy: percent error abs value of obs-expected/expected*100

Unit prefixes

Prefix Factor Scientific Notation mega (M) = 1,000,000 = 1 × 10⁶ kilo (k) = 1,000 = 1 × 10³ deci (d) = 1E-1 centi (c) = 0.01 = 1 × 10⁻² milli (m) = 0.001 = 1 × 10⁻³ micro (μ) = 0.000001 = 1 × 10⁻⁶ nano (n) = 1 × 10^-9 femto (f) = 1*10^-12 atto (a) = 1E-15 zepto (a) = 1E-18

Procedures for Experiment 7: Beer's Law

Prepare the stock standard solution. Calibrate the spectrometer with different concentrations of Allura Red AC dye. Use the spectrometer to determine the absorbance of the varying concentrations of the dye. Prepare standard concentrations of Gatorade and Powerade. Use the spectrometer to determine the absorbance of the Gatorade and Powerade.

What experimental components hindered the launch of the pipet rockets in experiment 5

Presence of water/water vapor, exposure to the atmosphere, letting gas out, etc.

Q test

Q=gap/range A statistical method used to determine if a data point can be rejected.

Qcal, Qsol, and Qrxn relationship

Qrxn = -(Qcal + Qsol) In endothermic reaction, heat is taken up from surroundings such as the solution and outside of calorimeter for the reaction. In exothermic reaction, heat is released to the surroundings such as the solution and outside of calorimeter from the reaction.

Explain what happens to light in a green solution

ROYGBV Green light passes through, but ROYBV are abasorbed

Reactions for Experiment 6: Thermochemistry

Reaction 1: Dissolution of solid sodium hydroxide Reaction 2: Neutralization of liquid sodium hydroxide and hydrochloric acid Reaction 3: Dissolution and neutralization of solid sodium hydroxide and hydrochloric acid

Colors and wavelengths

Red-Violet 400-750

Reactions in Experiment 5: Rockets

Redox: Zinc and HCl Decomposition: Hydrogen peroxide

Solubility

Reflects how easily these associations can form. It can be measured as the concentration of solute in a saturated solution at a specified temperature.

speed of light=(wavelength)(frequency)

Relationship between speed of light, wavelength and frequency

Does making a bond release or require energy?

Release; bond is a more stable form.

What are important precautions before using a hot plate?

Remember that the ceramic top of the hot plate, and any glassware heated by the hot plate will look the same when hot as cold, and will not cool down until well after the hot plate has been shut off. Never leave the hot plate turned on an unattended. Set up your work space with the hot plate in a secure location away from the edge of the bench so that you won't accidentally bump it and spill hot or flammable liquids. Set up your work space so that wires and cables cannot accidentally make contact with the ceramic surface and melt. Set up the work space so that flammable materials - notebooks, paper towels, other reagents, etc. - are far away from the hot plate to prevent them coming in contact with the hot surface.

Review Experiment 9, Lewis Structures and acidity based on compounds

Review it on lab site

What experimental uncertainty is reduced by rinsing the buret with the sulfuric acid solution before filling it?

Rinsing the buret with the sulfuric acid solution before filling it ensures that there is no excess moisture in the buret that will affect the concentration of the sulfuric acid.

What ingredients were in Rolaids that were not in the TUMS or Equate? Did this impact the pH curve? How? Ask your TA to show you data if you don't have this data yourself.

Rolaids: CaCO and Mg(OH)2 Equate: CaCO

25 degrees celsius (298K)

Room temperature

2.18x10^-18

Rydberg constant

How are the terms in the Rydberg equation defined? How can they be used to determine the starting and/or ending energy levels of an electronic transition?

Rydberg= Change in E = RH(2.18x10^-18)((1/nf^2)-1/ni^2)) For hydrogen nf=2

Thiocynate ion

SCN⁻ reacted with ion III to produce a red complex ion in experiment 7.

Experiment 2

Scientific Measurement and Error: To learn the use of common scientific glassware and learn the difference between precision and error.

Identify the end point of a conductivity titration. Compare both methods used in data analysis and assess the accuracy of different methods.

set the end points equal to each other to solve for x or the titration volume.

Procedures for Experiment 6: Thermochemistry

Set up the calorimeter. Perform Reaction 1 in the calorimeter and record temperature values. Perform Reaction 2 in the calorimeter and record temperature values. Perform Reaction 3 in the calorimeter and record temperature values.

Suppose you and your partner accidentally added sulfuric acid to the distilled water in the beaker instead of barium hydroxide; how would the shape of the conductivity plot change and why?

Since sulfuric acid is also aqueous, the acid would dissociate into its ionic components in solution. The shape of the conductivity plot would remain the same because the conductivity would be high before any base has been added because the solution is separated into ions, and the conductivity would continually decrease as barium hydroxide was added as the sulfate ions in solution bond with barium ions. The conductivity would then rise again after reaching the minimum conductivity and the end point of titration because barium hydroxide would continue to dissociate in solution after all sulfate ions have been bonded to barium ions.

Which of the following is a behavior that can pose a safety risk in the laboratory environment?

Sitting on lab benches, lab floors, or hallway floors, while waiting for lab to begin or for another student to finish. Leaving your lab drawer open while you set up your apparatus and obtain your reagents. Staying focused on your own experiment and not being distracted by what nearby groups are doing. Looking away from your work to answer a question from your TA or lab partner. Moving rapidly around the lab to be sure to finish the experiment in time.

What is a precipitate?

Solid that forms in a solution in a chemical reaction.

Dissolution

Solvent dissolves the substances that are eventually going to react. Involves the breaking of ionic bonds or inter-molecular forces and the formation of new associations between solute and solvent.

Solutes and solvents

Solvents are always greater in quantity In an example of an aqueous solution of NaCl, water is the solvent

4.184J/g x degree Celsius

Specific heat of water

Experiment 8

Spectroscopy: To use the spectroscope to compare various continuous emission sources, to obtain the atomic line spectra of light emitted from discharge tubes, and to calculate the photon wavelengths, frequencies, and energies from the line spectra data.

standard enthalpy change (ΔH)

Standard enthalpy changes refer to reactions done under standard conditions, and with everything present in their standard states. Standard conditions are: -298 K (25°C) -a pressure of 1 atm

Std. deviation formula

Std Dev=√(sum of the differences between the mean and individual results)/(# of results - 1) *Note that Std Dev for experiments are always sample Std Dev not population Std Dev

Conductivity graph shape if titrant and analyte were switched

Still the same, as you would still begin with a certain level of conductivity and slowly lose it since the same reaction will still occur, followed by an increase in conductivity after the completion. The idea does not change - the same thing is occuring. All you have done is switched which one you are titrating with. Therefore, your graph will have a similar shape (negative slope followed by a positive slope)

If a reaction is exothermic, what happens to the heat of each species?

Surroundings absorb heat and system releases heat.

Density, Temp, Volume relationship

Temp increases, Density decreases, Volume increases

How does temperature affect the density of a solution?

Temperature and density are inversely proportional. As temperature increases, density decreases.

Conductometric Titration

The addition of an acid to a base while measuring the conductivity unit it reaches a minimum to determine the concentration of the base in its solution.

To carry out Experiment 6 quantitatively, one major adjustment was made to the procedure followed in Experiment 2. That adjustment was: Select one: A. None of these is true. B. Calculations were made in moles rather than in grams. C. All solutions were equilibrated to room temperature before beginning the experiment. D. The thermometers were calibrated to give accurate temperature readings in °C. E. The calorimeter was calibrated to account for heat loss from the system.

The calorimeter was calibrated to account for heat loss from the system.

precipitate

solid product of a reaction of two solutions

Why do bond-breaking reactions require energy?

The atoms are more stable when bonded because they are attracted to each other.

Purpose of the blank cuvet (Beer's Law)

The blank is used to calibrate the spectrometer based on a solution with no analyte present so we can compare the solutions that do contain the analyte. (To measure the background absorbance in the cuvet and solution)

Which equipment in this experiment required calibration?

The calorimeter

To carry out Experiment 6 quantitatively, one major adjustment was made to the procedure followed in Experiment 2. That adjustment was:

The calorimeter was calibrated to account for heat loss from the system.

What is the effect of a wrong maximum wavelength in the Beer's law experiment?

The concentration will be affected, which will affect the slope of the absorbance vs. concentration graph

Results

The crushed tablets increased the pH faster than the whole tablet

What is the purpose of preparing standard solutions in this experiment? Why were crystals of NaSCN added to each cuvette? What chemical species was measured by Beer's Law? What property of this species made it a good choice as the molecule of study? What is the relationship of this species to the measurement of iron in the herb sample?

The crystals react with the iron to turn the solution red. The crystals react with the iron. Concentration of Fe3+ was calculated

Why do we use two styrofoam cups in a calorimeter set up?

The cups are great insulators and release little heat to the surroundings.

Resistance

The degree to which something opposes the passage of an electrical current that uses the unit of ohms.

Why were you asked to full the pipet bulb up with water before adding the gases?

The displacement of water allowed us to determine how much gas was being collected.

Heat or work

The energy transferred between a system and its surroundings measured in joules (J)

Conclusion from Experiment 6: Thermochemistry

The enthalpy changes of the three reactions with sodium hydroxide were calculated by using change in temperature through calorimetry. This calculation of enthalpy change through change in temperature in exothermic reactions demonstrates Hess's Law by showing, with minimal variance from theoretical values, that the sum of the change in enthalpy of two reactions is equal to the change in enthalpy for that combined reaction.

What is used in the decomposition of hydrogen peroxide into water and oxygen?

The enzyme catalase acts as a catalyst, which lowers the activation barrier for the reaction. Otherwise, the reaction would occur very slowly and we would've been stuck in lab for dayzz.

Stoichiometry

The precise numerical relationship between quantities of reactants and products in a chemical reaction.

Heat capacity

The magnitude of the eat energy flow that accompanies an increase in temperature depends on both the mass and the identity of the substance involved.

Enthalpy change (heat of reaction)

The measure of the amount of heat given off or absorbed in any chemical reaction

path length

The path length of the light through the solution (cm)

Conclusion for Experiment 8: Spectroscopy

The position of an emission spectra on a spectroscope can provide sufficient data to determine the wavelength of a light source, which can be used to determine frequency, energy, and energy levels of electrons; the spectrometer provides a more accurate wavelength through the optical fiber, which provides sufficient data to determine the color of emission lines of a light source. By using both instruments, the researchers could more accurately predict the identity of the unknown mixture.

Purpose of Experiment 7: Beer's Law

The purpose of this experiment is to design an experiment to determine the concentration of Allura Red AC dye in Gatorade and Powerade by utilizing Beer's Law. Data will be used with Beer's Law in order to compare the amount of dye in Gatorade and Powerade by measuring the absorbance values of dilutions of red Gatorade and Powerade and plugging those absorbance values into the calibration curve regression line. This experiment also allows the researchers to compare diluted concentrations and neat concentrations in order to determine the amount of Allura Red AC in both red Gatorade and Powerade.

Purpose of Experiment 1: Mass, Volume and Density

The purpose of this experiment is to determine the density of water at room temperature to understand how temperature affects density. This lab is important for understanding how solutes can affect density, and for the researcher to have a better understanding of precision and accuracy.

Purpose of Experiment 4: Conductometric Titrations

The purpose of this experiment is to monitor the dissolution of barium hydroxide (a conductive solution) and then to perform a titration with sulfuric acid. After the titration, the researchers are meant to observe the change in conductivity of the solution as the ion concentration decreases. Initially, the dissolution will contain barium and hydroxide ions, and then, upon adding the sulfuric acid, molecular water and barium sulfate will form, decreasing the concentration of the barium and hydroxide ions. The conductivity will be measured using a conductivity probe, which detects ions in solution. Because ions in solution generate electricity, I hypothesize that a decrease in ion concentration would decrease conductivity of the solution.

Purpose of Experiment 2: Aqueous reactions

The purpose of this experiment is to use calorimetry to understand the temperature changes that occur in a chemical reaction in aqueous solution. This lab is important because it allows the researchers to link observable changes and molecular changes in a chemical reaction. Measuring the change in temperature of several chemical reactions in aqueous solution.

Purpose of Experiment 8: Spectroscopy

The purpose of this experiment is utilize spectroscopy through observing the continuous and line spectra of different mixtures to determine the wavelengths, frequencies, and energies of the different mixtures and to identify unknown mixtures. Comparative observations and measurements will allow the researchers to make connections between observed line and emission spectra and energy levels.

Purpose for experiment 6: Thermochemistry

The purpose of this lab is to determine the enthalpy change of the dissolution of sodium hydroxide, the neutralization of hydrochloric acid by sodium hydroxide, and the dissolution and neutralization of sodium hydroxide by hydrochloric acid. A calorimeter will be used to monitor the temperature changes of each of the reactions. In order to accurately and precisely measure the temperature of the reactions, a temperature probe with be used that connects to the computer and consistently records the temperature and the calorimeter provides precise results.

Purpose of Experiment 5: Gas Forming Reactions and Rockets

The purpose of this lab is to launch a pipette-bulb rocket using the products of a combustion reaction. To obtain the fuel for the rocket, two gas-producing reactions will be conducted in which the products will be used to perform the combustion reaction necessary to propel the rocket. The order of addition of O2 and H2 will be compared in the combustion reaction to see which gas being added first will produce the farthest rocket launch.

In a determination of the mass of Fe per 100 g of oregano, the result is calculated to be ~10% too low when compared with the USDA Nutrient Database. The most likely experimental error to explain this result would be:

The pyrolysis of the oregano sample was incomplete, so more mass was diluted in the 1.0 M HCl

Limiting reactant

The reactant that runs out first

System

The reactants and products that are in the reaction

Circle (O)

The stability detector signal on an analytical balance that appears to the left of the numbers of the mass displayed when the balance has stabilized.

Why do you need a stir bar in the calorimeter?

The stir bar distributes the heat throughout the calorimeter.

Emission

The release of energy

Accuracy

The reliability of the data based on its deviation from the "true" or "literature" values.

Precision

The repeatably of the measurement, the relative reliability of the data based on standard deviation

Transmission diffraction grating

The separating device in a spectroscope

A student creates the following graph after an experiment measuring the density of water. Suppose the thermometer the student used was improperly calibrated and always read a value 3.5 degrees below the true temperature. Which of the following statements would be true? Select one: A. The slope of the regression line would be correct, but the intercept would read a value that was greater than the true value. B. The slope of the regression line would be correct, but the intercept would read a value that was less than the true value. C. The intercept of the regression line would be correct, but the slope would read a value that was greater than the true value. D. The intercept of the regression line would be correct, but the slope would read a value that was less than the true value.

The slope of the regression line would be correct, but the intercept would read a value that was less than the true value.

Dissolution

The solvent dissolves the substance that are eventually going to react.

What instrument requires calibration in this experiment? How is it the same or different than the calibration done in Experiments 6 and 7?

The spectroscope needs calibration form the fluorescent light, we make a calibration curve to calculate wavelength. It's different because it's giving us a new value.

Consider the following scenario: A student has prepared a series of analytical solutions to be run on an instrument in another room. The student has worn gloves throughout the preparation of the solutions, and has wiped up all drips and spills that occurred during that process. The student removes her gloves before leaving the lab room and carries her solutions in scintillation vials in a large clean beaker to the room where the instrument is located. Once in the new room, the student obtains a new pair of gloves before dispensing the solutions for analysis. What changes could be made to improve her procedures?

The student could have chosen a plastic bin, or other less breakable container to carry her solutions to the instrument so that she wasn't carrying glassware with her bare hands. The student could have worn a single glove on the hand she used for transporting the solutions to the instrument room, and used her non-gloved hand for opening doors and pushing elevator buttons. The student could have worked with her lab partner so that one of them could carry the materials with gloved hands, while the other opened doors and pressed elevator buttons with non-gloved hands

Thermochemistry

The study of the heat energy involved in chemical reactions and changes of physical state.

system

The system is the part of the universe being studied, while the surroundings are the rest of the universe that interacts with the system.

Absorption

The taking in of energy

combustion

The type of equation that reacts a substance with elemental oxygen

Describe the Balmer series and how to recognize it through experimental observations.

The visible spectrum of light from hydrogen displays four wavelengths, 410 nm, 434 nm, 486 nm, and 656 nm, that correspond to emissions of photons by electrons in excited states transitioning to the quantum level described by the principal quantum number n equals 2.[1] There are also a number of ultraviolet Balmer lines with wavelengths shorter than 400 nm.

What is the end point of titration?

The volume of titrant necessary to reach the lowest conductivity in an acid base titration.

How can the components of a mixture be identified using a flame test? What observations assist in drawing conclusions about the components of the mixture? What observations are most helpful? Accurate? Can you identify the relative quantities of each component, or are you only able to identify presence or absence?

The wavelengths that correlate with the energy states can be used along with the color you observe with your naked eye. You cannot identify the quantities due to the lack of information, but you can identify whether it is present or not.

Which of the following is a true statement about the bright yellow flame seen during a flame test of a 1 M solution of NaCl in a Meker burner flame?

The yellow color is characteristic of the changes in energy of an electron in the Na+ metal ion.

Experiment 6

Thermochemistry: to introduce the concept of thermochemistry, to illustrate the additivity of heats of reaction (Hess's Law) and to define and investigate exothermic and endothermic reactions.

How the energy level of an electron related to the energy of a photon?

They are limited by orbitals.They need a specific amount of energy to jump form one orbital to the next.

How is the spectroscopy done in Experiment 8 different from the measurements made in Experiment 7. In each experiment, what property of light is measured? What property of the molecule is associated with that property of the light?

This experiment is measuring the wavelength of light where as experiment 7 is measuring the absorption of light. The energy level of the molecule is associated with wavelength while the concentration of ion is associated with absorbency.

Significant Figures

Those digits in a measurement known with certainty plus the first estimated digit.

Conclusion of Experiment 4: Conductometric Titrations

Through the utilization of titration to perform a neutralization reaction, it was determined that conductivity of a solution and ion concentration of a solution are directly proportional.

Why stir bar in calorimeter

To ensure the reaction goes to completion and the solution is homogeneous. Steady stir rate without having to lift lid: less heat loss and reduction of human error

Calorimetry

To measure changes in temperature due to a reaction in which an insulated Styrofoam cup is used to create a closed system do that the heat transfer in a reaction can be measured with a thermometer

Suppose a beaker of solid reagent drops onto the bench and cracks. What is the best way to dispose of this?

To the extent possible, solid reagent should be added to the solid waste container and broken glass should be added to the glass waste. Hazardous materials should never be added to glass waste, and broken glass should only be allowed in solid waste with the TA's permission.

The following three actions could produce a significant source of error in the results for Experiment 5: Losing H2 gas because it is much less dense than air. Collecting gases while the reaction is still hot, resulting in mostly H2O vapor in the bulb. Leaving moisture on the spark gun tip before firing. Select one: True False

True

a. 1:1 b. 2:1 (Correct) c. The answer can't be determined from the information given. d. 1:2 e. 2:3 f. 3:2

Two of the above

In the reaction described above, the molecular equation is NaHCO3 (aq) + HCl (aq) → NaCl (aq) + H2O (l) + CO2 (g). Based on this equation and the observations of the reaction, the spectator ions in the ionic equation would be:

Two of the above: Na and Cl

Based on your observations in Experiment 5, an exothermic reaction may be identified via observation in the lab when it: Select one: A. Produces bubbles. B. Causes a loud popping noise. C. Grows cold. D. Forms a precipitate. E. Dissolves a solid reactant. F. Two of these answers are correct. G. Causes water condensation farther downstream H. Three of these answers are correct.

Two of these answers are correct.

Spectator ions

Unreacted ions in a chemical reaction.

Analytical balance

Used to measure weight in the chemistry lab

What is the most important consideration to preserve safety when it is necessary to feed glass tubing, thermometers, or other apparatus through a rubber stopper?

Using the correct hand position so that if something goes wrong you can avoid coming into contact with broken or sharp ends.

how to calculate volume from Buret segment

Vburet-Vwater-Vdisp 40L Buret-20Lwater-22Lwater after adding a marble 20L water...2L marble (bowling ball...)

400-800nm

Visible light

Standard Deviation

the measure of scatter of measured values about a mean. the smaller the STDEV the more precise the results. s=(sum of squares of deviation from the mean/# of observations-1)^1/2 n-1= degrees of freedom If n>10 than the data should be discarded

What were the technical challenges of this experiment?

Volume change was really small,

Calculations for Experiment 8: Spectroscopy

Wavelength = [ (Lowest position on spectroscope) - (Y-intercept from calibration equation) ] / (slope of calibration equation) (Speed of light) / (wavelength) = frequency of photon

What reagents were used in this experiment? What made these reagents particularly appropriate for this experiment? Was there something that made them problematic?

We had sulfuric acid and Barium Hydroxide, they were good because they we an acid and a base.

Balanced equation

the number of atoms of each element in an equation is the same on both sides.

When should you not wear gloves in the laboratory setting?

When entering data into your ELN on your laptop When writing notes on scratch paper using a pen and paper (Essentially handling materials that you will bring in/out of a lab)

When should you not wear gloves in the laboratory setting?

When entering data into your ELN on your laptop. When writing notes on scratch paper using a pen and paper.

Electrolyte

When the cations and anions in a solution are uniformly dispersed

When should you be sure to use a sealed container and/or secondary containment in the laboratory?

When transporting materials from one lab room to another.

Precipitation

When two aqueous solutions react to form a solid.

For which of the following situations should you be sure to notify your TA and fill out an incident report form?

You begin to feel faint and dizzy in lab because you had to skip lunch. You accidentally pick up a beaker from the hot plate, not realizing that it was already hot, and the edge of the beaker leaves a small red mark on your thumb. During lab check-out at the end of the semester, your lab partner accidentally drops a beaker, and a small chip of glass causes a scratch on your ankle because you weren't wearing socks. During check-in you discover a broken funnel in your drawer, and the broken end of the stem causes a small nick through your glove. You arrive in lab, but realize that your cold medicine is making you feel groggy. If your ailment does not originate in lab, you must still let your TA know and he will propose an excused absence. If you cannot drive, you should not come to lab. No matter how small the injury, you must fill out an incident report.

How can the enthalpy change of a reaction be predicted by using known data from 2 or more different reactions - theoretically and experimentally?

You can compare it with the literature data or measure the heat lost and subtract the sum of products- sum of reactants= change in heat.

How to determine metal ion of a flame if multiple metal ions have the same color

You could try to continue this approach by using a spectrometer to compare with more detail, or you could proceed to test its physical qualities (lustrous, ductile, shiny, density).

How does an experimenter distinguish between energy change in the reaction and the energy change in the surroundings?

You have to calculate the heat loss due to the calorimeter, qcal and the heat gained by the solution qsln

Oxidation-Reduction reaction

Zn + HCl --> ZnCl2 + H2 electrons are passed form one element to another.

Spectroscope

a box with a slit at one end to let in light and a light separating device at the other end.

Fuel Cell

a catalyst can be used to regulate the rate of combustion so that energy is produced at a safe and predictable rate.

Why does the dried herb need to be pyrolyzed? What is the importance of each step in this procedure (e.g. beginning with a cool flame, then moving to a hot flame, etc.)? What observations allow one to identify a cool/hot flame? If the flame is not as desired, how can it be adjusted? Are there chemical reactions happening inside the crucible during the heating stages? If so, what are the desired products? What is the purpose of adding HCl, water, and NaSCN to the pyrolyzed herb sample?

a cool flame- yellow flame medium-blue flame adjusted by oxygen opening

work

a force that is applied to an object that moves the object

Conductivity

a measurement of the ability of a substance to conduct electrical current and its unit of measurement is siemens (S)

Conductivity

a measurement of the ability of a substance to conduct electrical current. It is the reciprocal of resistivity (resistance)

Anion

a negative ion

Diffraction grating

a piece of glass or plastic that has a series of very fine scratches or grooves cut into its surface

Cation

a positive ion

Photodiode

a semiconductor diode that, when exposed to light, generates a potential difference or changes its electrical resistance.

pH meter

a sensor that detects the concentration of H+ ions, which may be the reactants or products of some types of reactions including acid-base and gas forming reactions.

standard solution

a solution containing a precisely known concentration of an element or a substance.

Consider the following compounds: I. ammonium pentanoate CH3(CH2)3CO2NH4 II. n-pentanol CH3(CH2)3CH2OH III. pentanoic acid CH3(CH2)3CO2H IV. pentanal CH3(CH2)3CHO

a. II. b. IV. c. I. and III. will have equally strong conductivity d. None of these will have any measurable conductivity because none is soluble. e. I. (Correct) f. III. g. All of these will be equally soluble. h. II. and IV. will have equally strong conductivity

Which item used during Experiment 8 required calibration?

a. The fluorescent light. b. The flame emission tests. c. The hydrogen lamp. d. The spectroscope. (Correct)

Define acid-base reactions and neutralization reactions and identify specific reactions of this type via chemical equations or specific experimental observations.

acid and base produce water and a salt.

Density vs. Temp. and Volume

air occupies more volume when heated; this is why hot air balloons float (heated air is less dense than surrounding air).

Spectator ions

appear on both sides of the overall ionic equation Ex. w/ NaCl(aq) and AgNO3(aq) Na+ & NO3-

chem reaction types for_____

aqueous-precipitaion, acid-base, complexation, and gas forming, and exo/endo

electrolyte

when cations and anions are uniformly dispersed in solution, meaning it contains moving charges capable of carrying an electric current.

Mean

average- sum of measured values divided by the number of measurements

Path length

b - the [blank] of the light through the solution contained in the cuvette. Usually equals 1.00cm. Measured in cm.

state function?

basis for hess is law, enthalpy is independent of pathway it only depends on the difference of E between the reactants and products

bromothymol blue

blue basic--> yellow acid

Concentration

c - in units of molarity

What samples were used for observations of flame emission spectra? What property of these materials made them appropriate for this experiment? What property of these materials was observed with the naked eye? What was observed with the spectroscope? Are they the same or different? Why?

candle->was observed with spectroscope while salts where observed by the eye and spectroscope. The different salts produced different energies and different wavelengths.

What are the technical challenges of this lab? How are they overcome or minimized?

challenges included: limiting reagent or pyrolysis of herb still having liquid in it.

Neutralization Reaction

characterized by the formation of covalent, neutral water molecules from acidic hydronium ions and basic hydroxide ions.

end point

where the two trendlines intersect or where the moles of titrant are stoichiometrically equivalent to the moles of base. Set trendlines equal to each other. mx +b = mx+b x=(b2-b1)/(m1=m2)

complexation

complexation reactions form chemical complexes due to the increased concentration of reactive elements that result in flooding. The resulting ion is called a complex ion, and it features a noticeably brighter shade of color.

Electrodes

conductors of electricity

Pyrolysis

decomposition brought about by high temperatures

Stoichiometry

defined as the precise numerical relationship between quantities of reactants and products in a chemical reaction.

Law of conservation of matter

dictates that the reactants and products in an equation for a chemical reaction must be balanced, meaning the number of atoms of each element must be the same on both sides of the equation. Atoms can be neither created or destroyed.

Understand the construction and use of a spectroscope. How does the spectroscope convert the light from a particular source into a spectrum, set of bright lines, or both? Why do different light sources produce different spectra?

diffraction device used to see the different types of wavelengths transmitted

The temperature at the start of a reaction was 26.5°C and at the end of the reaction was 18.5°C. Based on these observations the reaction of sodium bicarbonate with citric acid would be: Select one: A. exothermic, because energy is transferred from the reaction to the surroundings. B. exothermic, because energy is transferred to the reaction from the surroundings. C. endothermic, because energy is transferred from the reaction to the surroundings. D. endothermic, because energy is transferred to the reaction from the surroundings.

endothermic, because energy is transferred to the reaction from the surroundings.

Describe the electronic processes associated with absorption or emission of radiation. Which process is associated with an electron moving to a higher energy level?

gain energy by absorbing light to jump to antoher elvel.

Relate reaction equations to specific experimental observations.

gas forming- bubbles acid base- produced water dissociation- creates ions dissovle

3.5 g of sodium bicarbonate is added to a calorimeter containing 30 mL of 0.5 M HCl at 22 °C. During the reaction, bubbles appear in a steady stream, and the solution remains transparent. Based on these observations the reaction would be classified as

gas-forming

What is the purpose of a calibration curve?

general method for determining the concentration of a substance in an unknown sample by comparing the unknown to a set of standard samples of known concentration.

qsolution = m x C x change in temperature

heat gained by the solution (an equation)

specific heat

heat required to raise one gram one degree C (Joules)

Solution

homogeneous mixture of two or more substanaces

Precision

how close a group of measurements are to each other

Species after a reaction

if exothermic, heat of species decreases if endothermic, heat of species increases

Catalyst

increases the rate of the reaction. In this experiment it is yeast.

Random

indeterminate error- arises from limitations in the ability to make physical measurements. It is always present and cannot be accounted for explicitly. You can only read a ruler to 1.46 units leaving uncertainty in the last digit. *Affect the precision

Calorimeter why in exp 6

insulator used trap heat of a reaction so it can be measured used in exp 6 to measure trap the heat of reaction so that is can be measured to determine the change in enthalpy

Soluble Ionic Compound

it dissociates into cations and anions when dissolved in water.

Why is enthalpy a state function?

it is not pathway dependent. It doesn't matter what steps are taken to get there

Why Pyrolysis (in case of experiment 7)

it is to removed the organic material of the herb sample so that the iron content can be tested

Which reaction types were most energetic? What observations allow an experimenter to assess how energetic a reaction is?

loud, traveled quickly, warm best combinations were: 4:2 hydrogen to oxygen ratio with Oxygen collected first

Density

mass/volume SI unit= kg/m3 cgs unit = g/cm3

Gas Electrode

most widely employed ion-selective electrode for measuring pH.

Accuracy

nearness to "true" value

Decomposition reaction

occurs when one reactant breaks down into two or more products. Ex: 2KClO3 -> 2KCl + 3O2 (2H2O2-->2H2O+O2 in Chem 101L)

combustion

reaction by mixing Oxygen and Hydrogen, produces water and CO2. Exothermic

Cation vs ANion

plus = cation

Gas forming Reactions

produce insoluble gas as a product

gas forming

produces gas like CO2

Equations for Experiment 6: Thermochemistry

qcal = | qcold + qhot | q = mcDT ccal = (Dqcal) / (DTcold) Tmax = y intercept for equation when temperature begins to decrease qsoln = (msoln) * (DT) * (cH2O) qrxn = - | qsoln + qcal | DH = (qrxn) / (moles of reagent)

qrxn/n because q=h under constant pressure

Coefficient of Variation

relative standard deviation offers a measure of precision as a percentage of the value measured. CV=100*(s/mean)

Spectator ions

remaining ions that do not interact and remain in the solution in the same hydrated states as before the reaction. Not involved in chemical change.

Precision

reproduciblity of a method

Two ionic solutes are mixed in an aqueous solution

results in two different hydrated cations and two different hydrated anions. If strong enough solute-solute interaction occurs between any anion pair, a chemical reaction results and a new product is formed.

Acid + base =

salt + water

Balmer Series

series of spectral emissions lines of hydrogen that result from the energy transition from each level to two

Solute vs. Solvent

solute is present in smaller amounts while the solvent is present in larger amounts

How does one calculate the concentration of a solution prepared by dilution of a stock solution? By combination of a solution with a diluent? By dissolving a solid?

solution- M1V1=M2V2 solid-

What is the larger quantity: solvent or solute?

solvent

Surroundings

space and matter outside of the system

Standard deviation equation

square root of [ (the sum of x - mean)^squared ] / (n-1)

Thermochemistry

study of heat energy involved in chemical reactions and changes of physical state

Chemical reaction

substances are changed into other substances by addition to, separation of, or rearrangement of the atoms involved.

Two students carry out the same experiment, but the densities calculated by the first student are always 0.05 g/mL larger than those calculated by the second student for the same temperatures. The sources of error for the first student would be characterized as ________________, which would mostly affect the ________________ of the reported results.

systematic, accuracy

Change in temperature

t(final)-t(initial)

Specific heat

the amount of heat energy required to raise the temperature of one gram of the substance by one degree celsius and is given in the unit joules (J) per gram per degree celsius.

Standard heat of formation

the change in enthalpy when *one mole of a substance* is formed from its pure elements under standard conditions.

Standard heat of formation

the energy to form 1 mole of compound from its elements in their standard states

Meniscus

the surface of water/aqueous solution is curved in a buret due to the wetting of the glass walls by the solution. The curved surface is called...

Why fill the pipet bulbs with water

this is used to trap the gases into the bulb for collection and also to indicate how much gas is being collected as the water is displaced

Calculating change in enthalpy

∆Hf⁰(products)-∆Hf⁰(reactants)

colorimetry

to answer the question of how much of a product there is we use a dye that reacts with this product alone we use this colorimetry is the systematic measurement of absorbance by a colored solution; light passes through a cuvette and hits a photodiode the resulting intensity is used to determine concentration;

In Experiment 7, the purpose of creating the Beer's Law plot of absorbance vs. concentration of [FeSCN]2+ is best described as:

to determine the mM concentration of [FeSCN]2+ in a solution prepared from a parsley or oregano sample

3.5 g of white solid is added to a calorimeter containing 30 mL of 0.5 M HCl at 22 °C. During the reaction, bubbles appear in a steady stream, and the solution remains transparent. Based on these observations the reaction would be classified as: Select one: A. gas-forming B. complexation C. precipitation D. two of the above E. acid-base F. none of the above

two of the above

Find change in h of liquid water to h2 and o2

two steps h2o liquid to gas h2o--> standard states h2+.5o2

Honor Code

violations: -concepts may be discussed with partner or ta, but you must have work that reflects your understanding -ideas in report must be your own -allowing students to use your work -using old lab reports -old lab manual

What were the experimental challenges of this experiment? What sources of error played a major role in the outcome? Were there any variables that weren't fully accounted for in the setup?

water got into pippette, gases were contaminated from air, gases could escape, H2 was less dense than air.

whole vs crushed

whole took longer and was slightly less steep s curves for both still just the bottom half of crushed was shorter the tops ended at the same magnitude just different times

Molar Extinction coefficient

x - defines how strongly hte solution being studied absorbs light at a particular wavelength. This is unique for each different chemical at each different wavelength.

A student creates the following graph after an experiment measuring the density of water. In that experiment, the mass was measured to the third decimal place, the ~8 mL volume to the second decimal place, and the temperature to the first decimal place. Based on this information, how should the student label the axes?

y-axis: density (g/mL) with 3 significant figures x-axis: temperature (degrees C) with 3 significant figures

How is the mg of Fe in 100 g of herb calculated from experimental results? Can the transmittance of a solution be predicted from a reference value of mg Fe/100 g herb?

you do x over 100mg and set that as a ratio = to calculated grams of Iron/grams of Parsley/Oregano and solve for the x. If you worked backwards you could solve for A in A=ebc

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