Semester 1 Final Exam [PDF]

South Pasadena • AP Chemistry

Name

Semester 1 Final Exam

Period

Date

PRACTICE

TEST

Part 1 – Multiple Choice You should allocate 45 minutes to finish this portion of the test. No calculator should be used. A periodic table and data table will be provided. Select the answer that best responds to each question. 1. A 12.0 g sample of a hydrate of cobalt(II) chloride, CoCl2·nH2O, was heated, driving off all the water. The mass of the remaining solid CoCl2 (molar mass 130) was 6.5 g. What is the formula of the hydrate? (A) CoCl2·3H2O (B) CoCl2·6H2O (C) CoCl2·9H2O (D) CoCl2·12H2O 2. A 50.0 mL sample of a Cu(NO3)2 solution, which is a blue solution, and a NaOH solution, which is colorless, are combined forming a blue Cu(OH)2 (molar mass 81.5) precipitate. The 0.815 g precipitate is collected through filtration, and the colorless filtrate is set apart. What is the concentration of the original Cu(NO3)2 solution? (A) 0.10 M (B) 0.20 M (C) 0.40 M (D) The concentration of Cu(NO3)2 solution cannot be determined because it was the excess reactant. 3. A student prepared various solutions of CuBr2 and measured their absorbance at 635 nm. Absorbance

Concentration

0.0030 2 × 10−3 M 0.0075 5 × 10−3 M 0.0150 1 × 10−2 M What is the concentration of a CuBr2 solution with an absorbance of 0.0135? (A) 4 × 10−4 M (B) 3 × 10−3 M (C) 9 × 10−3 M (D) 2 × 10−2 M

4. A student placed 0.0243 g Mg in 50.0 mL of a 0.200 M HCl solution, producing H2 gas according to the following reaction: Mg (s) + 2 HCl (aq) → H2 (g) + MgCl2 (aq) What is the volume of H2 (g) produced at 300 K and 0.800 atm? (A) 10.0 mL (B) 30.0 mL (C) 100. mL (D) 300. mL 5. A student placed a sample of water under a bell jar, and used a vacuum pump to remove the air under the jar, lowering the pressure. The student claims that the water is boiling as bubbles are seen in the sample of water. Which of the following describes the student’s claim? (A) This is a chemical process as the hydrogen bonds in the water sample are being broken to form the gas. (B) This is a chemical process as water is breaking covalent bonds to become hydrogen and oxygen gases. (C) This is a physical process as inter-particle attractions between water molecules are weakening to become a gas. (D) This is a physical process as the water molecules move faster to become a gas. 6. A sample of solid calcium carbonate was added to vinegar. What is the net ionic equation for this reaction? (A) CaCO3 (s) + 2 H+ (aq) → H2CO3 (aq) + Ca2+ (aq) (B) CaCO3 (s) + 2 HC2H3O2 (aq) → H2CO3 (aq) + Ca2+ (aq) + 2 C2H3O2− (aq) (C) CaCO3 (s) + 2 HC2H3O2 (aq) → H2O (ℓ) + CO2 (g) + Ca2+ (aq) + 2 C2H3O2− (aq) (D) CO32− (aq) + 2 H+ (aq) → H2O (ℓ) + CO2 (g)

9. The following kinetics data was collected for the reaction 2 A → 3 B. Time

[A]

0s 0.100 M 0.50 s 0.070 M What is the rate of formation of B during this time? (A) 0.02 M/s (B) 0.06 M/s (C) 0.09 M/s (D) 0.14 M/s 10. Consider the following rate data for the reaction 2A + 2 B → C. Trial

[A] (M)

[B] (M)

1 0.20 0.20 2 0.40 0.40 3 0.60 0.20 What is the rate law of the reaction? (A) Rate = k[A]1[B]1 (B) Rate = k[A]2[B]0 (C) Rate = k[A]2[B]1 (D) Rate = k[A]3[B]2

Rate (M/s)

R 4R 9R

Time

[A]

ln[A]

1/[A]

0.00 s 1.0 M 0.0 1.0 M−1 0.20 s 0.4 M −1.0 2.5 M−1 What is the magnitude of the rate constant, k? (A) 2.5 (B) 3.0 (C) 5.0 (D) 12.5 12. The mechanism for the reaction X → Y is given: (1) X → A (2) A → B (3) B → Y The potential energy graph for this process is shown below.

Potential energy

8. What is the sum of the coefficients when the following redox reaction is balanced with lowest whole number coefficients using the half-reaction method? MnO4− (aq) + H2O2 (aq) → Mn2+ (aq) + O2 (g) (A) 7 (B) 14 (C) 21 (D) 28

11. Data for the first order reaction A → B is shown below.

Reaction progress

List the substances in increasing potential energy. (A) A < X < B < Y (B) X < A < B < Y (C) Y < B < A < X (D) Y < B < X < A 13. Below, the 1/[A] vs. time graph for the second order reaction 2A → B. Expt 1

1/[A]

7. In which of the following process does nitrogen have the greatest increase in its oxidation state? (A) N2 → NO2 (B) NH3 → NO3− (C) NO → N2O5 (D) N2H4 → N2O4

Expt 2

Time

Which of the following changes could have been made between experiments 1 and 2? (A) Experiment 1 had a catalyst in the reaction mixture, while Experiment 2 did not. (B) Experiment 1 had a higher initial concentration of A than Experiment 2. (C) Experiment 1 had a lower initial concentration of B than Experiment 2. (D) Experiment 1 was performed at a lower temperature than Experiment 2.

14. Consider the following proposed mechanism: (1) 2 NO2  N2O4 Fast Equil. (2) N2O4 + H2O → HNO2 + HNO3 Slow What is the rate law for this mechanism? (A) Rate = k[H2O] (B) Rate = k[NO2][H2O] (C) Rate = k[NO2]2 (D) Rate = k[NO2]2[H2O] 15. The value of Ka for HF is 7 × 10−4, and the Ksp for PbF2 is 4 × 10−8. What is the approximate value of Kc for the following reaction? 2 HF (aq) + Pb2+ (aq)  PbF2 (s) + 2 H+ (aq) (A) 2.8 × 10−11 (B) 1.8 ×10−4 (C) 8.0 ×10−2 (D) 1.2 × 101 16. Consider the following reaction: 180 kJ + CaCO3 (s) CaO (s) + CO2 (g) Which of the following changes would result in the greatest amount of CaO (s)? (A) Adding CaCO3 (s) to the reaction mixture. (B) Decrease the volume of the container. (C) Raising the temperature. (D) None of the changes would increase the amount of CaO (s). 17. Consider the following reversible reaction: 2 SO2 (g) + O2 (g)  2 SO3 (g) Samples of SO2 (g), O2 (g), and SO3 (g) are all placed in a container so each has a partial pressure of 1.0 atm. After equilibrium has been reached, the partial pressure of SO3 (g) is 1.33 atm. What is the value of Kp for this process? (A) 3.0 (B) 4.8 (C) 6.0 (D) 12 18. A saturated solution of which of the following has the highest pH? (A) Hg(OH)2 Ksp = 3 × 10−26 (B) Sn(OH)2 Ksp = 3 × 10−27 (C) Cr(OH)3 Ksp = 7 × 10−31 (D) Al(OH)3 Ksp = 2 × 10−32

19. BaSO4 is expected to be more soluble in which of the following solutions than in pure water? (A) BaCl2 (B) HCl (C) KCl (D) KHSO4 20. What is the maximum amount of KCl can be added to a 50.0 mL sample of a 0.200 M Pb(NO3)2 solution before a precipitate forms? The Ksp of PbCl2 is 1.3 ×10−5. (A) 0.00040 mol (B) 0.0020 mol (C) 0.0080 mol (D) 0.010 mol 21. Which one of the following has a pH > 7? (A) 0.10 M CH3NH2 (B) 0.10 M CH3OH (C) 0.10 M NaClO3 (D) 0.10 M NH4Cl 22. What is the pH of a solution when 900 mL of water is added to 100 mL of a 0.010 M NaOH solution? (A) 2.0 (B) 3.0 (C) 11.0 (D) 12.0 23. A 0.20 M solution of a weak acid has a pH = 3.0. What is the value of Ka for this solution? (A) 2.0 × 10−7 (B) 5.0 × 10−6 (C) 2.0 × 10−4 (D) 5.0 × 10−3 24. 0.100 M of solutions of which of the following substances has the highest pH? The Ka of HClO2 = 1.2 × 10−2, and the Kb of NH3 is 1.8 × 10−5. (A) HClO2 (B) KClO2 (C) NH4Cl (D) NH4ClO2

25. Consider a 0.100 M solution of KHSO4. Which of the following has the greatest concentration in this solution? (A) H2SO4 (B) HSO4− (C) OH− (D) SO42−

28. What volume of a 0.15 M KOH solution is needed to titrate a 40.0 mL sample of a 0.75 M HClO2 to its half equivalence (halfway) point? (A) 50 mL (B) 100 mL (C) 150 mL (D) 200 mL

26. Which of the following lists acids in decreasing acid strength? (A) HBrO2 > HBrO > HIO > HI (B) HI > HBrO2 > HBrO > HIO (C) HI > HIO > HBrO > HBrO2 (D) HIO > HBrO > HBrO2 > HI

29. A 0.100 M HNO2 solution is prepared, and NaOH is added until the pH of the mixture is 5.00. How do the concentrations of the species compare? The pKa of HNO2 is 3.40. (A) H+ = NO2− > HNO2 (B) HNO2 = NO2− > H+ (C) HNO2 > H+ = NO2− (D) NO2− > HNO2 > H+

27. 200 mL of which of the following solutions would require the greatest volume of 0.050 M NaOH to reach a pH 7? (A) 0.100 mol HNO2 (B) 0.100 mol HNO2 + 0.100 mol NaNO2 (C) 0.100 mol HNO3 (D) 0.100 mol NaNO3

30. Which of the following mixtures would produce a solution with the greatest buffering capacity? (A) 0.100 mol HNO2 + 0.050 mol NaNO2 (B) 0.100 mol HNO2 + 0.050 mol NaOH (C) 0.100 mol HNO2 + 0.100 mol NaNO2 (D) 0.100 mol HNO2 + 0.100 mol NaOH

Part 2 – Free Response You should allocate 50 minutes to finish this portion of the test. You may use a scientific calculator. A periodic table and data table will be provided. Respond to each part of the questions completely. Be sure to show your work clearly for questions that involve calculators. 31. A student prepares a 100.0 mL solution of potassium permanganate, KMnO4, using 10.0 mg KMnO4 (molar mass 158.04 g/mol). (a) Find the concentration of MnO4− in mol/L.

(b) The absorbance spectrum over visible light for the solution is shown below. 2.0

Absorbance

1.5

1.0

Color

Wavelengths

Reds Oranges Yellows Greens Blues Violets

625-740 nm 590-625 nm 565-590 nm 520-565 nm 440-520 nm 380-440 nm

0.5

0.0 400

i.

500 600 Wavelength (nm)

700

What color is this solution? Justify your answer using the spectrum.

ii. The colorimeter that the student is using measures absorbance at 430 nm, 470 nm, 565 nm, and 635 nm, and the student decides to use 565 nm. Is this the best wavelength at which the colorimeter be set for this experiment? Justify your answer.

iii. At 565 nm, the absorbance of the KMnO4 solution is found to be 0.800. The student then transfers 5.00 mL of the KMnO4 solution to a test tube, and adds 5.00 mL of distilled water to it. What is the absorbance of this new solution in the test tube?

A student performs an experiment by adding a solution of tin(II) chloride, SnCl2, to the solution of potassium permanganate, KMnO4, undergoing the following reaction: … MnO4− (aq) + … Sn2+ (aq) → … Mn2+ (aq) + … Sn4+ (aq) (c) For the reaction that occurs, i. Write the balanced net ionic equation for this reduction-oxidation process. Use the method of halfreactions.

ii. How many electrons are transferred in the equation shown? (d) The student performs an experiment by observing how the absorbance changes immediately after the solutions are combined. The data for the experiment and their graphs are given below.

i.

Time (s)

Absorbance

ln(Absorbance)

1/Absorbance

0 1 2 3 4 5 6 7 8

0.8000 0.4852 0.2943 0.1785 0.1083 0.0657 0.0398 0.0242 0.0147

−0.22 −0.72 −1.22 −1.72 −2.22 −2.72 −3.22 −3.72 −4.22

1.25 2.06 3.40 5.60 9.24 15.23 25.11 41.39 68.25

The rate law depends only on [MnO4−] (in other words, it is zero order with respect to the other reactants). Write the rate law for this reaction. Justify your answer.

ii. Find the value of the rate constant, k.

iii. What is the absorbance of the solution at 10.0 seconds?

32. Ascorbic acid, HC6H7O6, a weak acid, has an acid-dissociation constant, Ka, 7.9 × 10−5 at 25°C. a. Write the expression for the reaction for the ascorbate ion, C6H7O6−, in water.

b. Write the expression of the base dissociation constant, Kb, for C6H7O6− and find its value.

c. Two 100.0 mL solutions of 0.500 M NaC6H7O6 are prepared, and labeled beakers A and B. i. What is the pH of the solutions?

ii. 0.010 mol NaOH is added to beaker A. What is the pH of this solution?

iii. 0.010 mol HCl is added to beaker B. What is the pH of this solution?

d. Vitamin C is a nutritional supplement consisting of ascorbic acid, the ascorbate ion, or both. A particular product claims to be “buffered,” with the following information from the product label for one tablet: Vitamin C (as ascorbic acid and sodium ascorbate) 500 mg (HC6H7O6 and C6H7O6−) Sodium (as sodium ascorbate) 23 mg (Na+) i. Calculate the moles of ascorbic acid and sodium ascorbate in this tablet.

ii. Find the pH when this tablet is fully dissolved in 250. mL distilled water. Assume that no other ingredient in the tablet affects the pH of the system, and that volume change due to the tablet is negligible.

iii. Does the pH increase, decrease, or remain the same if two tablets are dissolved? Explain.

e. A second H+ can be removed from ascorbic acid, and has the following dissociation equation: C6H7O6− (aq) + H2O (ℓ)  C6H6O62− (aq) + H3O+ (aq) Ka = 1.6 × 10−12 Provide a quantitative explanation for why this is reaction is ignored when determining the pH of a NaC6H7O6 solution, as in part c.i.

33. Consider the salt, Ag2CO3, which has a solubility product, Ksp, of 8.1 × 10−12 at 25°C. a. Saturated solutions of Ag2CO3 are prepared by adding the salt to pure water. i. Write the dissociation equation for Ag2CO3 in pure water.

ii. Calculate the molar solubility of Ag2CO3 in pure water.

iii. Predict whether the [Ag+] will increase, decrease, or remain the same when the following are added.  AgClO3  HNO3  Na2CO3 b. The Ksp of AgCl is 1.6 × 10−10 at 25°C. i. A 1.0 L solution contains 0.100 mol Cl− and 0.100 mol CO32−. As AgNO3 is added to the solution, will Ag2CO3 or AgCl precipitate first? Explain using calculations.

ii. What is the value of equilibrium constant for the following reaction: 2 AgCl + CO32−  Ag2CO3 + 2 Cl−

South Pasadena • AP Chemistry

Name

Semester 1 Final Exam

Period

Date

TEST BLUEPRINT Part 1: Multiple Choice  Format: 30 questions, four answer choices: (A)-(D)  Expected time: 45 minutes  Allowed resources: Periodic Table, Equations and Constants. No calculators.  Topics: o Unit 1 – 8 questions o Unit 2 – 6 questions o Unit 3 – 6 questions o Unit 4 – 6 questions o Unit 5 – 4 questions Part 2: Free Response  Format: o 2 long questions (5-8 parts) o 1 short question (2-4 parts)  Expected time: 50 minutes  Allowed resources: Periodic Table, Equations and Constants, and scientific calculators.  Topics: o Unit 1 – 12 points o Unit 2 – 10 points o Unit 3 – 10 points o Unit 4 – 10 points o Unit 5 – 6 points