Chem 101L Final

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, producing solid barium sulfate and water. The end point of the titration would be expected at a volume of: (Hint: No calculators are needed) Select one: A. 6.053 mL B. 10.15 mL C. 0.002024 mL D. 12.11 mL

12.11 mL

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 38.60 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 18.3 mL and the next mark up. What volume of water is contained in the buret segment?

20.35 mL

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

2:1

8.92 x 10-4 g mL-1 oC-1 represents the change in density as temperature increases.

8.92 x 10-4 g mL-1 oC-1 represents the change in density as temperature increases.Using the graph shown from an experiment measuring the density of water, what would be the correct value, units, and significance of the slope of the trendline?

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

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 1.5 degrees above the true temperature. Which of the following statements would be true?

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

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

In the conductivity titration of barium hydroxide and sulfuric acid, 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: (Hint: no calculator required.) Select one: A. 12.11 mL B. 0.002024 mL C. 6.053 mL D. 10.15 mL

A. 12.11 mL

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

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

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: Select one: A. endothermic, because energy is transferred from the reaction to the surroundings. B. exothermic, because energy is transferred from the reaction to the surroundings. C. endothermic, because energy is transferred to the reaction from the surroundings. D. exothermic, because energy is transferred to the reaction from the surroundings.

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

The molecular equation for the reaction previously done in Experiment 4 is: Ba(OH)2 (aq) + H2SO4 (aq) → BaSO4 (s) + 2 H2O (l). How is conductivity reflected in the net ionic equation? Select one: 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. Therefore, the net ionic equation will have no spectator ions, and only the reactants will be written as ions in solution. 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 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. D. 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.

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.

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: Select one: A. 7.85 B. 7.30 C. 8.45 D. The answer cannot be determined from the information provided.

C. 8.45

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. -9.36 kJ B. 9.38 kJ C. 9.36 kJ D. 17.7 kJ E. -9.38 kJ F. -17.7 kJ

C. 9.36 kJ

A 2.00-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. 1.23 mg B. 123 mg C. None of these. D. 15.1 mg E. 15.1 g F. 0.615 mg

C. None of these.

A buret segment with a largest volume increment of 35.00 mL is filled with pure water to approximately half way between 19.2 and the mark above it. After adding the probe, the meniscus moves to halfway between 18.9 and the mark just under it. What is the original volume of the water in the buret? Select one: A. 16.05 mL B. 15.75 mL C. 16.15 D. 15.85 mL

D. 15.85 mL

Using the graph provided, for the reaction of 1.25 g of sodium bicarbonate with 150 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.) A. None of these B. 945 °C/mol C. 11.7 °C/mol D. 605 °C/mol E. 7.20 °C/mol Feedback

D. 605 °C/mol

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: Select one: A. 0.0363 M B. 0.0698 M C. 5.65 x 10-5 M D. 0.0698 mM E. 0.0363 mM

E. 0.0363 mM

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

E. Br-

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

F. 2 H2O2 (aq) →catalase→ 2 H2O (l) + O2 (g)

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 Select one: A. 1 B. 2 C. 3 D. 4 E. 5 F. 6 G. The answer cannot be determined from the information given.

F. 6

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: Select one: A. Na+ B. Cl- C. H+ D. CO2 E. H2O F. Two of the above G. Three of the above H. None of the above

F. Two of the above

In Experiment 7, the ultimate 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. Select one: True False

False

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.

I. Both A and E are true.

During a conductivity titration, 15.0 mL of AgNO3 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 the previously seen minimum as expected as lithium chloride 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 silver nitrate, the experimenter added tap water. B. The silver nitrate and sulfuric acid were mistakenly combined in the beaker, and the water was used to fill the buret. C. The experimenter mistakenly added twice as much silver nitrate to the beaker. D. The lithium chloride was added to the beaker while the silver nitrate was used to fill the buret.

Instead of adding distilled water to the silver nitrate, the experimenter added tap water.

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.

Only V and VII are correct.

d. 534 nm

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 5.34 mm on the spectroscope scale? Select one: a. 0.366 nm b. 533 nm c. 455 nm d. 534 nm e. The answer cannot be determined from the information given

Two calorimetry trials were performed with barium hydroxide and ammonium chloride. The first, using 2.0 g of barium hydroxide with 10 mL of a 0.5 M ammonium chloride solution showed a temperature change from 23.2 oC to 12.5 oC. The second trial showed a decreased from 25.7 oC to 20.4 oC after addition another 10 mL of 0.5 M ammonium chloride to 1.0 g of barium hydroxide in the calorimeter. What does this observation suggest about the reaction. Select one: A. The reaction of barium hydroxide and ammonium chloride is exothermic. The energy expelled depends on the states of matter of the substances being reacted. B. The reaction of barium hydroxide and ammonium chloride is exothermic. The energy expelled is related to the concentration of the reactants mixed. C. The reaction of barium hydroxide and ammonium chloride is endothermic. The energy absorbed by the reaction is reliant on the concentration of the reagents mixed. D. The reaction of barium hydroxide and ammonium chloride is endothermic. The energy absorbed is directly proportional to the moles of the substances reacting. E. Three of these answers are correct. F. The reaction of barium hydroxide and ammonium chloride is endothermic. The energy absorbed is directly related to the difference in the initial temperature upon mixing the substances.

The reaction of barium hydroxide and ammonium chloride is endothermic. The energy absorbed is directly proportional to the moles of the substances reacting.

G. A and D only.

The titration of barium hydroxide with sulfuric acid is a bit different than that of silver nitrate and lithium chloride. The balanced chemical equation and the 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 present in solution when 6.62 mL of titrant had been added? Ba(OH)2 (aq) + H2SO4 (aq) → BaSO4 (s) + 2 H2O (l) Select one: A. Ba2+ B. SO42- C. H+ D. OH- E. A, B, and C. F. B and C only. G. A and D only. H. None of these

In Experiment 7, the experimental purpose of creating the Beer's Law plot of absorbance vs. concentration of Allura Red AC was to determine the molar concentration of Allura Red AC in a solution prepared from a soft drink sample, so that the mg/serving could be calculated.Select one: True/False

True

What does CV measure? How do the numbers correlate? a. None of the above are correct. b. CV measures precision. The higher the CV, the higher the precision. c. CV measures precision. The higher the CV, the lower the precision. d. CV measures accuracy. The higher the CV, the higher the accuracy. e. CV measures accuracy. The lower the CV, the higher the accuracy. Feedback

c. CV measures precision. The higher the CV, the lower the precision.

The reaction of zinc with hydrlochloric acid seen in experiment 5 produces hydrogen gas via the equation featured below. Which of the following species gets reduced? Zn (s) + 2 HCl (aq) → H2 (g) + ZnCl2 (aq) Select one: a. Cl- b. All of the above c. H+ d. Two of the above e. Zn2+

c. H+

A colored metal salt was dissolved in 120 mL of distilled water. Using a known spectroscopic method, the metal was shown to have a concentration of 6.102 x 10-5 M. Titration of the sample with a known hydrochloric acid solution showed 2.3 x10-5 mol of the anion. What is the identity of the salt tested? (Hint: Pay attention to units. While a calculator can help it is not necessary.) Select one: a. MnCO3 b. CuCl2 c. Cu2SO4 d. Cr(OH)3 e. NiF2

d. Cr(OH)3

Which item used during Experiment 8 required calibration? Select one: a. The spectrophotometer. b. The incandescent light. c. The hydrogen lamp. d. The spectroscope.

d. The spectroscope.

5.224 g of water in a buret segment with a largest volume increment of 50.00 mL shows a corrected volume of 44.33 mL at a certain temperature. How many significant figures will be present in the correct representation of the density?

e. 3

Which of the following can best be described as measuring accuracy? Select one: a. two of the above b. systemic error c. random error d. all the of the above e. none of the above f. Standard Deviation g. Coefficient of Variation h. Percent Error

h. Percent Error