chem 101L
how to calculate percent difference
(actual - theoretical) / theoretical then multiply by 100
can be rearranged
(concentration of analyze) = (A-b)/m
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
2:1
In calorimetry, the enthalpy change of the reaction, q rxn, is defined to be: (Select all that apply.)
-(qsoln + qcal), heat gained or lost by the reaction
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, equation is qsoln = (m) (specific heat) (change in temperature)
Assume that an average adult male has a mass of 70 kg. How many grams of Allura Red AC does this adult need to consume before he reaches the ADI set by the WHO and FAO. (Assume 7 mg/kg/day).
.49 grams
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
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?
2
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
best ratio of hydrogen to oxygen
2:1
what is the reaction between Magnesium metal and hydrochloric acid
2Mg (s) + 2HCl (aq) ----> 2MgCl (aq) + H2 (g)
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?
4.15*10^-3 M
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? (y=0.0112x + 0.6556
479 nm
measure NaOH by difference. The NaOH bottle is 5.042 g, once the NaOH removed it is 4.812 g. Calculate mass of NaOH.
5.042-4.812 = 0.230 g
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.)
7.53 mg
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 lowest energy would have a spectroscope position of:
8.45
the data is plotted as a scatter plot and fitted to a line with the equation: y=0.0084x -1.237. What is the wavelength that corresponds with a spec position of 6.57
929 nm
In some circumstances, materials that are being heated in the lab could catch fire. If a flammable substance in a beaker should catch fire while you are working but the flames are relatively contained, which method must never be used for extinguishing the flame? Select one: a. Use water from the sink nearest the bench to douse the flames. Correct b. Turn off the heat source immediately, and use a watch glass to cover the beaker and minimize the oxygen around the flame. c. Use the chemical fire extinguisher located in the lab. Pull the pin, aim the nozzle into the beaker, and pull the lever.
A
define the variables of Beer's Law
A = εlc
he 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.
To carry out a calorimetry experiment quantitatively, which of the following would be necessary (select all correct answers): A. The thermometer must be calibrated to give accurate temperature readings in °C. B. The calorimeter must be calibrated to account for heat loss from the system. Correct C. Calculations must be made in moles rather than in grams. D. None of these is true. E. All solutions must be equilibrated to room temperature before beginning the experiment.
A, B, C, E
A
A= Absorbance = -log(l/l0) - the ration represents transmittance - l is the intensity of light passing through the sample over the l0, intensity of light passing through the blank
Which of the following is a behavior that can pose a safety risk in the laboratory environment? Select one or more: a. Looking away from your work to answer a question from your TA or lab partner. Correct b. Staying focused on your own experiment and not being distracted by what nearby groups are doing. CorrectWhile this may seem counterintuitive, in the lab it is important to be able to focus on your experiment and still have a clear sense of your surroundings and what other experimenters are doing. If you have a single-minded focus on your own work, you are likely to be the cause of an incident involving another group. c. Moving rapidly around the lab to be sure to finish the experiment in time. Correct d. Leaving your lab drawer open while you set up your apparatus and obtain your reagents. Correct e. Sitting on lab benches, lab floors, or hallway floors, while waiting for lab to begin or for another student to finish
ALL
Which of the following must be completed before taking the quiz? Select one or more: a. Put on gloves b. Tie back long hair. CorrectYou must be completely prepared for lab before beginning the quiz. Taking the quiz when you are not in complete lab attire is a violation of the Honor Code. c. Store your backpack, cell phone, jacket, and all other nonessential items in designated storage areas. CorrectYou must be completely prepared for lab before beginning the quiz. d. Put on your lab coat. CorrectYou must be completely prepared for lab before beginning the quiz. Taking the quiz when you are not in complete lab attire is a violation of the Honor Code. e. Put on your goggles. CorrectYou must be completely prepared for lab before beginning the quiz. Taking the quiz when you are not in complete lab attire is a violation of the Honor Code.
ALL BUT GLOVES
What is your BEST resource for understanding the nature of the chemical hazards of materials you work with in lab?
Safety Data Sheets (SDS)
experiment 4: equation between silver nitrate and lithium chloride
AgNO3 (aq) + LiCl (aq) -----> AgCl (s) + LiNO3 (aq)
How is the data improved by obtaining at least 4-5 measurements after the end point?
Allows for extrapolating back to find minimum conductivity with trendline
When dealing with hazardous materials generated in the lab, the two most important guidelines are: (Choose two.) Select one or more: a. Materials used in General Chemistry are generally nonhazardous, so most can go in the normal trash. b. Organize the experiment to generate the least amount of hazardous material possible. Correct c. When in doubt, dispose of materials as though they are the most hazardous type to be safe. d. Never dispose of anything without asking your TA for assistance. e. Collect ALL hazardous material for proper disposal. Correct
B and e
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 6.62 mL of titrant had been added?
Ba and OH
what is the balanced equation for the neutralization of barium hydroxide with sulfuric acid
Ba(OH) (aq) + H2SO4 (aq) ----> Ba(SO4) (s) + 2H2O (l)
n some circumstances, materials that are being heated in the lab could catch fire. If a flammable substance in a beaker should catch fire while you are working but the flames are relatively contained, what is a simple method for extinguishing the flame? Select one: a. Use the chemical fire extinguisher located in the lab. Pull the pin, aim the nozzle into the beaker, and pull the lever. b. Use water from the sink nearest the bench to douse the flames. c. Turn off the heat source immediately, and use a watch glass to cover the beaker and minimize the oxygen around the flame.
C
how was the calibration curve calculated?
Caculated from known concentrations of Allura Red AC
Experiment 7: What is Beer's Law?
Concentration of an analyte in a solution is directly proportional to amount of light absorbed or inversely proportional to amount of transmitted light
how to you calculate density and what units should be used?
D=M/V, kg/cm^3
Mg (s) and HCl is a _________ rxn
exothermic
experiment 6 dealt with all __________ reaction
exothermic
reaction of hydrogen and oxygen is a _________ reaction
exothermic
define random error
Error arises from uncontrolled and uncontrollable variables which has an equal chance of being positive or negative. This type of error cannot be detected and corrected. Examples include temperature fluctuations, incorrect readings, scale output that records various readings for the same mass.
define systematic error
Error that arises from a flaw in equipment or experiment design. They can be detected and correct. Usually has to do with own out equipment or incorrect calibrations.
sodium carbonate and distilled water is a _________ rxn
exothermic
forming bonds is a characteristic of
exothermic reactions
citric acid can be thought of as
H3+3 and C6H5O7
define accuracy
How close data measurements are from the accepted or "true" value.
what is the reaction between sodium bicarbonate and citric acid?
NaHCO3 + C6H5O7 ----> H2O + CO2 + Na3C6H5O7
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 of the sample is greater than 1.2 than you must dilute your sample even further. In order to dilute, you must calculate the necessary mL of diluent needed using the M1V1=M2V2 and add more distilled H20 using the micropippets; making sure to continue to use 4 significant figures.
experiment 6: what are the 3 chemical reactions used, and what Law does this represent?
NaOH(s) + H2O (l) ----> NaOH (aq) + H2O (l) NaOH (aq) + HCl (aq) ----> NaCl (aq) + H2O (l) NaOH (s) + HCl (aq) -----> NaCl (aq) + H2O (l)
When reading the label on a reagent container, what are the three most important pieces of information?
Name, concentration, Hazard Warnings
If the concentration of AgNO3 is 0.00503 M and the concentration of the LiCl solution is 0.00387 M, use the stoichiometry of your equation to predict the volume of lithium chloride needed to react with 9.98 mL of the silver nitrate solution.
LiCl = 13.0 mL
equation used to figure out known concentration
M1V1 = M2V2
what are metal qualities
Metals are lustrous, malleable, ductile, good conductors of heat and electricity. Solid at room temperature except for mercury
for the dissolution of ammonium chloride and sodium carbonate; what ions were produced
NH4+, Cl-, 2Na+, CO32-
when is it acceptable to eat at the lab bench?
NEVER! if you are hypoglycemic take your snack outside of the lab
Experiment 5: What role did the stoichiometry of the combustion reaction play in your predictions and/or your analysis of the results? How might other untracked variables have played a role?
Need two more moles of hydrogen gas for every 1 mole of oxygen gas, so I knew that more hydrogen was necessary. Furthermore, density played a role because hydrogen is less dense than air and needed to be added in the rocket first in order to avoid escaping.
stoichiometric and catalytic reactions
Stoichiometric reactions are consumed and used up, persisted throughout the experiment. Catalytic reactions involve a catalyst to speed up the chemical reactions and are not consumed in the reaction (so they are not written in the chemical equation). Added to increase the rate of the reaction without influencing the energies of the reactants or the products.
Can the Rydberg constant be used for mercury emission lines as well? (normally only hydrogen)
No, because the Rydberg only works with Bohr's model of one electron, cause after it starts gaining electrons it begins to break down
What phenomenon would cause you to see an emission of a specific wavelength of light from metal salts during the flame test
The electrons are excited due to the heat of the flame, therefore the flame will change color as the electrons move back down to ground state, having a specific frequency, wavelength, and energy of the photon released.
how to find the change in temperature DT
Tf - Ti
Experiment 8: Sources of error
The calibration of the spectroscope may not have been correct, skewing the rest of the data (systematic), electrical tube containing hydrogen gas did not emit enough gas to record accurate positions on the spectroscope, optical fiber was not calibrated correctly skewing the transmittance values for the flame test, observations of the flame were quick.
How is the data improved by adding smaller volumes near the predicted end point? Is there any advantage to making small volume additions all the time? Is there a disadvantage to always making small volume additions?
The data is improved because one can be much more precise to the predicted end point when adding smaller quantities of volumes. An advantage would be that one can be very precise if the predicted value has decimals or is a small number, however adding very small increments of volume is time consuming.
after you finish collecting you absorbance readings on the spectrophotometer, you notice a dark smudge on your cuvette you used to blank. How would you expect this to have affected your absorbance readings on samples you ran after the blank?
The effect of a dark smudge would be a significant decrease in the calibration measurement of absorbance, and subsequent samples in comparison would have a lower absorbance than they would have against a true blank. Because it is the blank cuvet, the following absorption measurements will be lower because the calibrated spectrometer thinks '0' absorbance is actually higher, say 10. Then, when the others are tested, instead of 20 absorbance, it will only be 10. (Just random numbers)
Should the slope of the trendlines in this experiment should be positive or negative? Why? If not, what reaction type do you think make the opposite slope?
The trend lines as the solution increases in temperature should be positive, however, the trend line used to calculate the extrapolated maximum temperature should be negative because the values used are when the temperature begins to level off and decrease. The trend line for an endothermic reaction should be negative because the temperature is decreasing due to heat being absorbed by the system from the surroundings.
What is a decomposition reaction?
When a compound is broken into it's component parts (AB→A+B) ex: CO2 -----> C (s) + O2(g)
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:
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.
Why is it important to NOT create a seal between the pipette bulb and the tubing when collecting oxygen gas
You should not create seal because the water is displaced by the oxygen collected, and if there is no opening the water cannot flow out of the tube.
When should you be sure to use a sealed container and/or secondary containment in the laboratory? Select one: a. When transporting materials from one lab room to another. Correct b. When heating materials over a Bunsen burner. c. When transporting materials from the hood to the bench. d. When heating a solution over a hot plate.
a
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. Which of the following changes could improve the student's procedure? (Check all that apply.) Select one or more: a. 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. b. The student should have kept her gloves on the entire time, as she was handling glassware and reagents. Therefore, that takes priority over any contact with doorknobs or elevator buttons, and gloves should be worn. Also, this would conserve one pair of gloves and keep them from being wasted. c. 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. d. 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. Correct e. No changes, the student handled the process correctly.
a, c, d
An electron moves from the ground state to an excited state of 5, is this emission or absorption, is the change positive or negative, is the electron more or less stable?
absorption, positive, less stable
what do calibration standards define
accuracy and quality of measurements
Should you add water to acid or acid to water?
add acid to water; this minimizes heat that can cause dangerous fumes or chemical reactions
how to calculate mean
add up all values and divide by the number of values.
how does temperature affect density
as temperature increases density decreases because molecules are farther apart and the volume is larger. When temperature decreases density increases because molecules slow down and pack tightly to each other, decreasing the volume.
In some circumstances, using the fire extinguisher found in the laboratory may be necessary. Which of the following scenarios represents an appropriate use of a fire extinguisher? Select one: a. A handful of paper towels was left too close to a Bunsen burner and caught fire on the lab bench. The flames are contained for the moment, but might spread to other lab notebooks and flammable materials on the bench. b. A handful of paper towels in the garbage can has caught fire. The fire is small and relatively contained within the trash can. CorrectThis fire is relatively small and contained and is a good candidate for the use of a fire extinguisher. c. Several bottles of reagents in the fume hood have caught fire and are in danger of creating an explosion. d. Fumes from a solution contained in a beaker have caught fire, and the fire seems to be contained to the beaker.
b. A handful of paper towels in the garbage can has caught fire. The fire is small and relatively contained within the trash can. CorrectThis fire is relatively small and contained and is a good candidate for the use of a fire extinguisher.
why is a catalyst needed in the decomposition of hydrogen peroxide to water and oxygen?
because the reaction is very slow and needed to sped up in order to undergo the experiment
why do we only record abosorbance at a wavelength that gives the greatest absorbance value (max wavelength)
because this is the wavelength in which the solution is the most sensitive to concentration changes
neutralization reactions are:
between an acid and a base, normally salt and water are produced. the cation from the base is combined with the anion from the acid (salt) and water is produced
what are the four wavelengths observed from hydrogen
blue, violet, yellow, green
The correct process for disposing of liquid waste containing hazardous material would be:
bring waste to liquid waste bottle, check to see if it's not too full and the liquid is in the funnel, check to see liquid waste bottle can be used for this specific waste, open the latch and pour, close the latch
what are some potential errors for experiment 4?
buret not calibrated (systematic), graduated cylinder not calibrated correctly (systematic)
what is a combination reaction ?
when two reactions come to form a product ex: 2H2 + O2 ----> 2H2O
when should you not wear gloves in the laboratory setting?
when using your laptop, opening the door
what is the purpose of the blank in Beer's law experiment
calibrate the spectrometer and take into account the abosrobancy of the glass or cracks
Consider your results and observations from the reaction of citric acid with sodium bicarbonate. What physical observations revealed that a reaction was taking place
carbon dioxide gas bubbles out of the solution; the sodium bicarbonate absorbed heat from the citric acid, causing temp to decrease
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, grows warm
based on observations in experiment 5, an exothermic reaction may be identified by
causes loud popping noise, grows warm
experiment 4: what is the endpoint and how do you calculate it?
where the moles of the titrant (lithium chloride) are stoichiometrically equivalent to the moles of analyze (silver nitrate). Should be a volume amount of lithium chloride added. equation: use the tow trendiness and then x= b2 - b1/ m1-m2
the most precise will have the lowest __________
coefficient of variation
after measuring absorbance vs. concentration you realized you had worked with the wrong wavelength max. Which of the following will get affected in the regression line for the calibration curve?
concentration
C
concentration (mol/L)
what causes absorption?
concentration is directly proportional to absorbance and indirectly proportional to transmittance. The higher the concentration, the higher the absorption and lower the transmittance
What experimental measure will change if water is added to immerse the conductivity sensor in the silver nitrate solution? Will this affect the end point of the titration?
concentration of ions will decrease because more solvent is present; will not effect endpoint
Why is it important to prevent mixing of the hydrogen peroxide with the zinc/acid mixture in the waste container
could cause a combustion reaction in the waste container
draw diagram for endothermic
diagram
draw diagram for exothermic
diagram
temperature and pressure are ________ related
directly
using you spectroscope you observe a light source and see several strong, distinct lines. Is this source continuous or discrete? Given a line with a wavelength corresponding to 500 nm, calculate the energy of the emitted light
discrete line spectra; 3.97*10^-19
In experiment 5 you were asked to fill up the pipet bulb with water before adding the gases. Why?
displacement of the water inside the bulb is how you know how much gas you collected. Can't see gas....
spectator ions
do not play a direct part in the reaction, can be eliminated
Ammonium chloride and distilled water is a ________ rxn
endothermic
sodium bicarbonate and citric acid is a ________ rxn
endothermic
breaking bonds is a characteristic of
endothermic reactions
why is enthalpy change considered a state function? How does this relate to Hess's Law?
enthalpy is the heat gained or lost at a constant pressure. It is a state function because the change depends only on the initial and final states of the system, not how the change occurred. This relates to Hess's Law because a reaction can undergo a lot of steps, but the overall enthalpy change equals the sum of the individual steps. (independent on number of steps or path)
the reaction between silver nitrate and lithium chloride is a
exchange reaction
All of 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. Losing O2 gas because it is much denser than air. Collecting gases while the reaction is still hot, resulting in mostly H2O vapor in the bulb.
false
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
true or false: to calculate temperature change you do initial temperature minus final
false
true or false: yeast was the catalyst of the decomposition of hydrogen peroxide into oxygen gas and water?
false; enzyme was catalase which comes from yeast, hence the formation of yeast bubbles
looking through your spectroscope you see several discrete, clearly defined lines. What is a possible source for this spectrum?
fluorescent light
does making a bond release or requiring energy
forming bonds releases energy
when a species gets reduced it
gains electrons
What would happen if you did not use a stopper in Reaction A
gases would be released into the surrounding environment
for exothermic reactions, the final temperature will be
higher
define precision
how close individual measurements are from each other. Can be determined by calculating mean, standard deviation, and CV
what is a combustion reaction ?
hydrocarbon (carbon and hydrogen) combine with oxygen to produce CO2 and H2O. Extremely exothermic, can produce a flame
more _______ is needed to propel the rocket
hydrogen because for every 1 mole of oxygen there needs to be 2 moles of hydrogen
_________ gas should be added before __________ to propel the rocket the farthest
hydrogen; oxygen; so hydrogen does not escape the rocket and the oxygen traps it
draw soluble chart
in notebook
experiment 2: Why does the data collection last for 4 minutes? Why not use a single measurement of temperature before and a single measurement after the reagents are mixed?
in order to make sure the reaction goes to completion (temp will start to go back to initial)
how to find displacement volume (Vd)
initial volume reading (Vi) - volume reading with T probe (VT)
what is a precipitate
insoluble solid
net ionic equations
ions directly part of the reaction
Why isn't it correct to use the minimum measured conductivity as the end point of the titration? To what extent would this affect the results of the experiment?
it is not correct to use the minimum measured conductivity as the end point of the titration because the true endpoint could be before or after the minimum conductivity reading. This would change the molar ratio
heat of formation is in
kJ/mol
what materials can you have at the lab bench?
laptop and calculator
how to find corrected volume with buret
largest volume increment (Vb) - volume reading with probe (VT) - displacement value (Vd)
Why does ice float?
less dense than water. The oxygen atoms repel one another causes the volume to increase and the density to decrease.
when a species gets oxidized it
loses electrons (becomes more positive)
for endothermic reactions, the final temperature will be
lower
Consider your results and observations from the reaction of solid magnesium with hydrochloric acid. What physical observations revealed that a reaction was taking place?
magnesium metal began to sizzle and smoke because it was being dissolved by the HCl; hydrogen gas bubbled out of the solution
what should you do if you get solution on your gloves and up your arm
notify the TA, rinse arm under distilled water for at least 15 min
ε
molar extinction coefficient (molar absorptivity) defines how strongly the analyze absorbs light at a particular wavelength M-1cm-1
given a photon emitted from a hydrogen lamp with a wavelength of 434 nm, identify the correct transition in the Balmer series (make sure final is 2)
n=5
for an endothermic reaction, the heat of the solution (q soln) will be _________
negative because the solution is losing heat and work to the reaction
for an exothermic reaction, the heat of the reaction (q rxn ) will be ___________
negative, because the reaction is releasing energy to the surroundings
broken glass should _______ to the solid waste
never
l
path length of light through the solution , 1.000 cm
for an endothermic reaction , the heat of the reaction (q rxn) will be __________
positive, because it is gaining heat and energy from the surroundings
for an exothermic reaction, the heat of the solution (q soln) will be ____________
positive, because the reaction is supplying the surroundings with energy
suppose you and your partner added lithium chloride in the beaker of water instead of sodium nitrate. How would the shape of the conductivity line change?
postive linear line
H2 and O2 gases were used to ________ the rocket, and they combine to form ________
propel; H2O(g)
in experiment 2, the system was the
reactants and products, direct reaction
why do bond forming reactions release energy
represents a stable configuration for atoms
breaking bonds__________ energy
requires energy; bonds do not spontaneously break
what are some potential errors for lab 6?
scale not being calibrated that was used to measure out NaOH (s) (systematic) which would have meant that more NaOH (s) would have been added in the reaction than necessary creating a very high final temperature. Thermometer was based too high in one trial (random), which meant that it would not pick up on a very large change in temperature.
how to calculate standard deviation
shows how close the data numbers are to each other (precision). 1. find mean 2. subtract mean from all numbers and square each value. 3. add up all square values. Divide this number the numbers in the data set minus 1 (n-1) 4. square root the new mean
experiment 6: Why do you weigh the solid NaOH by difference instead of directly weighing it on a weigh boat?
solid NaOH is hygroscopic and absorb water
in an aq solution of NaCl, is water the solute or solvent
solvent
which is larger quantity, solvent or solute
solvent (dissolving medium)
experiment 6: what is c cal
specific heat of the calorimeter
how to calculate specific heat of the reaction
specific heats of products - specific heats of reactants
Experiment 7: Potential errors?
spectrometer not calibrated correctly (systematic), concentration of sports drinks were not evenly distributed (systematic), using only one cuvette for gatorade and one for Powerade does not result in precise data, one cuvette was filled up higher than the other cuvette (systematic)
Which item used during Experiment 8 required calibration?
spectroscope (calibrated with the fluorescent light, the mercury emissions)
Experiment 8: Why was the spectroscope calibrated?
spectroscope has an arbitrary scale so one must plot the observed position of the line spectra with the reference values to find wavelengths of unknown light sources
What is the purpose of calibrating the spectroscope?
spectroscope has an arbitrary scale so one must plot the observed position of the line spectra with the reference values to find wavelengths of unknown light sources
in experiment 8, the wavelength (nm) was on the _________ axis and the position of the spectroscope (mm) was on the __________ axis
x-axis, y-axis
scale not being calibrated is a __________ error
systematic
what experimental components hindered the launch of the pipet rockets in experiment 5?
systematic: hydrogen and oxygen generated were not pure, some rockets had cracks in them (accuracy), presence of water or water vapor, letting gas out random: air vents that pushed the rockets, temperature fluctuations (precision)
for lab 1, what are some potential errors
temp probe and buret were not calibrated correctly (systematic); there were temperature fluctuations in the class environment (random)
conversions
tetra (10^12) giga (10^9) mega (10^6) kilo (10^3) base deci (10^-1) centi (10^-2) milli (10^-3) micro (10^-6) nano (10^-9) pico (10^-12) femto (10^-15) atto (10^-18)
experiment 4: What experimental uncertainty is reduced by rinsing the buret with the lithium chloride solution before filling it?
that the concentration of lithium chloride is what you expect it to be and there are not impurities
what's the purpose of the calibration curve?
the calibration curve was used to calculate the unknown concentration of two samples: red Powerade and red gatorade
calorimeters are not perfect insulators. What does that mean? How do we, as scientists, account for imperfect insulation?
the calorimeter is not perfect, meaning that some of the heat from the reaction will be lost to the calorimeter. Scientists account for imperfect insulation by calculating the q cal = c cal * DTrxn
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
the experimenter added tap water instead of distilled water (tap water has more ions in it and thus would have a higher conductivity)
What would happen if you used a stopper without a hole in Reaction A
the pressure would start to build up and cause an explotion
in an endothermic reaction
the system gains heat from the surroundings. There is more bond breaking than bond forming. The solution in the calorimeter loses heat because it is being supplied to the reaction. the products have more energy than the reactants.
in an exothermic reaction
the system gives off energy to the surroundings. There is more bond formation than breaking of bonds. The solution in the calorimeter heats up. The reactants have more energy than the products.
how to calculate coefficient of variation
this shows the variability and dispersion of data 1. find mean and standard deviation 2. standard deviation/ mean, and then multiply by 100
the second reaction is a stoichiometric redox reaction, Zn(s) + 2HCl (aq) ----> ZnCl2 (aq) + H2 (g)
this was in order to collect the hydrogen gas
Why do we move the hot plate and beaker and not the buret segment once the temperature reaches 80 degrees
to leave the burret as untouched as possible to eliminate errors that effect accuracy and precision
why do we use two cups in the coffee cup calorimeter setup
to limit the escape of heat, making results more accurate. Styrofoam was used because it's a good insulator of heat
Why do you need to wait another 1-2 minutes after attaching the stopper before you collect oxygen?
to make sure air in the tank is displaced by oxygen gas
Why should the water in the buret segment be below the level of water in the 600-mL beaker?
to make sure all of the boiled water surrounds the buret
experiment 1: In this experiment, why is the mass of the burette segment with water measured twice for each sample; once before and once after heating?
to make sure the water does not change due to evaporation and to be as precise as possible
Why is it important to wait at least two minutes after adding zinc to collect hydrogen
to make sure you are only collecting hydrogen gas and not water vapor or other impurities
why do you need a stir bar in the calorimeter
to thoroughly mix up reactants in order to a chemical reaction to occur
A solution containing an unknown metal ion is sprayed into an open flame, giving rise to an orange color by eye. Upon researching metal ions which burn with this color, you find several candidate ions which also burn orange color by eye. Upon researching metal ions which burn with this color, you find several candidate ions which also burn organs and are unsure how to identify the unknown. What test(s) would you preform to identify the identify of unknown?
use spectrometer to fine wavelength corresponding to peak in % transmittance vs. wavelength with known chemicals that produce orange and compare it to the unknown... you can test physical qualities of the unknown (lustrous, ductile, shiny, density) and compare to the known.
the surroundings was the
water, cups, everything outside of the cups
experiment 5: what catalyst did we use for the reaction 2H2O2(aq) ---> 2H20 (l) + O2 (g) , and why
we used the catalyst catalase (produced by yeast). We need to collect the oxygen for the experiment in a timely manner so the catalyst speeds up the reaction
what is solute
what is being dissolved in the solvent, smaller quantity
q cal is the heat lost to the calorimeter
will be positive in an exothermic reaction because the calorimeter is not a perfect insulator of heat and some heat will be lost. For an endothermic reaction, qcal will be negative because some of the heat from the calorimeter will be lost to the reaction.
dependent variable is what your are measuring and goes on the _______ axis while independent variable is what you manipulate and goes on the _______ axis
y axis, x axis
experiment 5: Why do you wait until the rate of bubbling slows in the reaction of yeast and hydrogen peroxide
you want to wait for the foam to stop forming so you can remove it
