Spring 2009 CH 302: 30 Practice Problems Covering the Equilbrium Problem Types You Will Find on Exam 2. Answer Key 1) The pH of an equimolar solution of acetic acid + sodium acetate is found to be 4.75. What will happen to the pH of this solution if we dilute it with water to twice the initial volume? A. The pH will rise and be higher than 4.75. B. The pH will fall and be lower than 4.75. C. The pH will remain 4.75. D. No answer is possible without knowing the actual initial concentrations. Answer: C 2) The pH of a solution that is 0.25 M (NH4)2SO4(aq) and 0.50 M NH3(aq) is: A. 4.75 B. 8.95 C. 9.25 D. 9.56 Answer: C 3) What will be the pH in a titration in which 5.0 mL of 0.120 M HNO3(aq) is added to 25.0 mL of 0.240 M KOH(aq)? A. 0.74 B. 13.26 C. 13.33 D. 13.38 Answer: B 4) The volume, in mL, calculated to one decimal point, of 0.25 M HCl(aq) required to reduce the pH of 50 mL of a 0.40 M ammonia solution to a value of 7.00 would be: A. 80.0 B. 79.6 C. 50.0 D. 49.8 Answer: B5) A buffer solution of volume 200.0 mL is 0.250 M Na2HPO4(aq) and 0.250 M KH2PO4(aq). The pH resulting from the addition of 50.0 mL of 0.100 M NaOH(aq) to the buffer solution will be A. 7.12 B. 7.21 C. 7.30 D. 12.77 Answer: C 6) After the addition of 150 mL of 0.100 M KOH(aq) to 100 mL of 0.100 M H2SO4(aq), A. the pH of the final solution will be 1.92. B. the pH of the final solution will be greater than 1.92, but less than 7.00. C. the pH of the final solution will be 7.00. D. the pH of the final solution will be greater than 7.00, but less than 13.00. Answer: A 7) The molar concentration (to two significant figures) of chloride ions in a saturated solution of silver chloride is: A. 0.8 × 10−10 mol·L−1 B. 1.6 × 10−10 mol·L−1 C. 0.8 × 10−5 mol·L−1 D. 1.3 × 10−5 mol·L−1 Answer: D 8) The molar concentration (to two significant figures) of iodide ions in a saturated solution of lead iodide is: A. 1.4 × 10−8 mol·L−1 B. 1.2 × 10−4 mol·L−1 C. 1.5 × 10−3 mol·L−1 D. 3.0 × 10−3 mol·L−1 Answer: D 9) What is the solubility of Ag2CrO4 (Ksp = 1.12 × 10−12) in grams per 100 mL of 0.100 M solution AgNO3? A. 1.5 × 10−9 B. 3.2 × 10−8 C. 3.7 × 10−9D. 1.8 × 10−8 Answer: C 10) When sodium nitrite is added to HNO2(aq), A. the equilibrium concentration of HCOOH(aq) decreases.B. the pH of the solution increases. C. the Ka increases. D. the pH of the solution does not change. E. the pH of the solution decreases. Answer: B 11) 100 mL of each of the following solutions is mixed; which one of the mixed solutions is a buffer? A. 1.0 M NH3(aq) + 0.6 M KOH(aq) B. 1.0 M NH4Cl(aq) + 1.0 M KOH(aq)C. 1.0 M NH3(aq) + 0.4 M HCl(aq) D. 1.0 M NH4Cl(aq) + 0.4 M HCl(aq) E. 1.0 M NH3(aq) + 1.0 M HCl(aq) Answer: C 12) Choose the effective pH range of an aniline/anilinium chloride buffer. The value of the Kb for aniline is 4.3 × 10–10. A. 3.6–5.6 B. 8.4–10.4 C. 1.1–3.1 D. 5.1–7.1 E. 10.1–12.1 Answer: A 13) Which of the following mixtures gives a buffer with a pH greater than 7.0? For HCNO, Ka = 2.2 × 10–4 and for NH3, Kb = 1.8 × 10–5. A. 10 mL of 0.1 M NH3(aq) + 10 mL of 0.1 M HCl(aq) B. 10 mL of 0.1 M HCNO(aq) + 10 mL of 0.1 M NaOH(aq)C. 10 mL of 0.1 M HCNO(aq) + 5.0 mL of 0.1 M NaOH(aq)D. 10 mL of 0.1 M NH3(aq) + 10 ml of 0.1 M HCNO(aq) E. 10 mL of 0.1 M NH3(aq) + 5.0 mL of 0.1 M HCl(aq)Answer: E 14) If a small amount of a strong base is added to buffer made up of a weak acid, HA, and the sodium salt of its conjugate base, NaA, the pH of the buffer solution does not change appreciably because A. the Ka of HA is changed. B. No reaction occurs. C. the strong base reacts with A– to give HA, which is a weak acid.D. the strong base reacts with HA to give AOH and H+. E. the strong base reacts with HA to give A–, which is a weak base. Answer: E 15) At the stoichiometric point in the titration of 0.130 M HCOOH(aq) with 0.130 M KOH(aq), A. the pH is 7.0. B. [HCOOH] = 0.0650 M. C. [HCO2–] = 0.130 M. D. the pH is greater than 7. E. the pH is less than 7. Answer: D 16) For the titration of 50.0 mL of 0.020 M aqueous salicylic acid with 0.020 M KOH(aq), calculate the pH after the addition of 55.0 mL of KOH(aq). For salycylic acid, pKa = 2.97. A. 10.98 B. 7.00 C. 11.26 D. 12.02 E. 12.30 Answer: A 17) The titration curve for the titration of 0.100 M H2SO3(aq) with 0.100 M KOH(aq) is given below.Estimate pKa1 and pKa2 of H2SO3. Answer Answer: pKa1 ~ 2.0 and pKa2 ~ 6.9 18) The titration curve for the titration of 0.100 M Na2CO3(aq) with 0.100 M HClO4(aq) is: The main species in the solution after the addition of 35 mL of HClO4 are A. HCO3–, H2CO3, Na+, and ClO4–.B. H2CO3, Na+, and ClO4–. C. CO32–, HCO3–, Na+, and ClO4–. D. CO32–, Na+, and ClO4–. E. HCO3–, Na+, and ClO4–. Answer: A 19) What is the relationship between the solubility in water, s, and Ksp for the ionic solid Ca3(PO4)2? A. Ksp = 72s5 B. Ksp = 5s C. Ksp = 6s2 D. Ksp = s5Answer: A 20) Which of the following water-insoluble salts is more soluble in 1.0 M HClO4(aq)? A. AgBr B. PbF2 C. Hg2Br2 D. PbI2 E. AgClO4 Answer: B 21) If equal volumes of 0.004 M Pb(NO3)2(aq) and 0.004 M KI(aq) are mixed, what reaction, if any, occurs? The value of Ksp for PbI2 is 1.4 × 10–8. A. The solution turns purple because of formation of I2.B. PbI2(s) precipitates. C. KNO3(s) precipitates. D. No reaction occurs. E. The value of Ksp changes to 9 × 10–9. Answer: D 22) If you wish to increase the solubility of silver benzoate, a preservative, you would A. add sodium hydroxide. B. decrease the pH. C. add sodium acetate. D. add sodium benzoate. E. add silver nitrate. Answer: B 23) Rank, from greater to least, the equilibrium concentration of species formed when 0.2M H2SO4 is placed in solution. Answer Answer: H+ > HSO4- > SO4= > OH- > H2SO4 24) You have watched a fellow student derive the exact solution for a dilute strong acid in water. Feel free to derive a similar solution for a dilute weak acid case (or look at the equation in the notes.) How many more unknowns are there for the dilute weak acid than the dilute weak acid? What …
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