McGill UniversityCHEM 120Acid Base & Buffers Questions ( WITH ANSWER KEY )

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Chapters 16 & 17 Practice Problems 1) Complete the following equation and list the conjugate acid/base pairs. H3O+ + Cl- + NH3 ↔ a) H2O + Cl- + NH4+ (NH3/H2O) (H3O+/NH4+) b) H3O+ + HCl + NH2- (N... H3, NH2-) (Cl-/H3O+) c) H2O + Cl- + NH4+ (H3O+/H2O) (NH4+/NH3) d) H2O + Cl- + NH4+ (NH4+/H2O) (H3O+/NH3) e) H2O + H2 + Cl- + NH2+ (H3O+/NH3) (NH2+/H2O) 2) Which of the following statements concerning aqueous solutions of salts is FALSE? a) For any salt of a strong acid and a strong base, the pH will be about 7. b) For any salt of a weak acid and a weak base, the pH will be about 7. c) For any salt of a strong acid and a weak base, the pH will be <7. d) For any salt of a weak acid and a strong base, the pH will be >7. e) none of these 3) If one mole of Ba(OH)2 is added to enough water to make 10 liters of solution, the pH of the resulting solution is: a) 13.0 b) 13.3 c) 12.5 d) 1.0 e) 0.7 4) What is the pH of a 0.380 M solution of ethylamine? Kb = 4.3 × 10-4 a) 10.2 b) 12.1 c) 8.5 d) 1.9 e) 5.5 5) For the following compound, predict whether the solution is acidic, basic or neutral and why: NaCl. a) basic because it is the salt of a weak acid b) acidic because it is a strong acid c) acidic because it is the salt of a weak base d) basic because it is a weak base e) neutral because there is no hydrolysis 6) Determine the pH of 263 ml of solution which has [NH4I] = 0.300 M. Kb = 1.74 × 10-5 for NH3(aq). a) 9.1 b) 11.4 c) 4.6 d) 2.6 e) 4.9 7) List the acids HBrO, HIO and HClO in order of increasing strength: a) HBrO < HIO < HClO b) HClO< HBrO < HIO c) HClO < HIO < HBrO d) HIO < HClO < HBrO e) HIO < HBrO < HClO 8) What is the pH of a solution prepared by mixing equal volumes of 0.10 M hydrochloric and 0.1 M hydrofluoric acid? [Ka for HF is 6.6 × 10-4] a) 1.6 b) 1.0 c) 1.3 d) 2.2 e) 5.0 9) A buffer was prepared by adding 2.4 g of ammonium nitrate (NH4NO3) to 100.0 mL of 0.30 M ammonia ( Kb =1.8 × 10-5). To this solution was then added 10.0 mL of 0.30 M sodium hydroxide, which caused a pH change of: a) 0.30 pH units b) 3.0 pH units c) 0.90 pH units d) 0.09 pH units e) zero 10) How many mL of 0.200 M acetic acid are mixed with 13.2 mL of 0.200 M sodium acetate to give a buffer with pH = 4.2? [pKa(CH3COOH) = 4.74] a) 13 mL b) 46 mL c) 18 mL d) 37 mL e) 3.8 mL 11) For the titration of HCl with NH3(aq), determine whether the solution at the equivalence point is acidic, basic or neutral and why: a) acidic because of hydrolysis of NH4+ b) acidic because of hydrolysis of Clc) basic because of hydrolysis of NH3 d) neutral salt of strong acid and strong base e) acidic because of hydrolysis of HCl 12) In the neutralization of 50.0 mL of 0.1 M BOH (a weak base with Kb = 1.6 × 10-7) with 0.10 M HNO3, the major species present in solution at the half-equivalence point are: a) B+ OH- H3O+ NO3- b) B+ H3O+ NO3- c) BOH B+ OH- NO3- d) BOH B+ H3O+ NO3- e) B+ OH- HNO3 13) Which species in the following reaction acts as a Lewis acid? CuSO4(s) + 4NH3(aq) → Cu(NH3)42+(aq) + SO42-(aq) a) NH3 b) SO42- c) Cu2+ d) Cu(NH3)42+ e) All are acids. 14) What is the pH of a 5 × 10-8 M aqueous solution of NaOH? a) 6.89 b) 7.30 c) 6.70 d) 7.11 e) 7.00 15) Which one of the following statements regarding pH colour indicators is correct? a) They are usually strong acids or strong bases b) They are always weak bases c) The colour change occurs over the pH range pKb ± 1 d) The colour change occurs over the pH range 1 ± pKb e) The colour change occurs over the pH range pKa ± 1 16) If 50 mL of a 0.1 M solution of ammonia (NH3, pKb = 4.74) is titrated with 0.25 M HCl, what is the pH at the equivalence point? a) 5.2 b) 8.8 c) 6.1 d) 7.9 e) 7.0 [Show More]

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