EXAM 1 1. Which of the following is not a Lewis base?(a) MeNH2 (b) H2O (c) ClO- (d) C5H5N (pyridine) (e) NH4+ 2. For pH calculations involving solutions of weak acids, it is frequently assumed that the H3O+formed by the auto-dissociation of water (10-7 M) is negligible. For which one of the following a situations is this approximation least likely to be true?(a) HA has Ka = 10-2 and the initial concentration of HA is 1.0 M.(b) HA has Ka = 10-2 and the initial concentration of HA is 0.0010 M.(c) HA has Ka = 10-9 and the initial concentration of HA is 1.0 M. (d) HA has Ka = 10-9 and the initial concentration of HA is 0.0010 M. 3. Which one of the solutions listed below has the lowest pH?(a) 0.100 M HCN(aq) (b) 0.100 M CH3CO2H(aq) (c) 0.100 M HOCl(aq)(d) 0.100 M NH4+(aq) (e) 0.100 M C5H5NH+ (aq) (pyridinium ion) 4. What is the pH of a 0.82 M HF(aq) solution?(a) 2.12 (b) 3.35 (c) 4.21 (d) 2.29 (e) 1.63 5. Which one of the fol owing is the strongest base in aqueous solution?(a) BrO- (b) ClO- (c) IO- (d) FO- (e) ClO2 6. What is the pH of a solution prepared by dissolving 3.4 x 10-4 mol of Ca(OH)2 in 375 mLwater? (a) 11.26 (b) 10.96 (c) 8.02 (d) 9.65 (e) 11.4 7. What is the pH of a buffer prepared from 0.225 mol H3PO4 and 0.105 mol NaOH in a total volume of 1200 mL? (a) 2.20 (b) 2.08 (c) 7.20 (d) 7.14 (e) 12.31 8. How many mols of NaOH would you add to 1.00 L of 0.16 M H3PO4(aq) to form a buffer with pH = 7.20? (a) 0.36 mol (b) 0.40 mol (c) 0.16 mol (d) 0.32 mol (e) 0.24 mol 9. The following salts were dissolved in water to form 0.050 M solutions. Order these solutionsby increasing pH. KCN CaBr2 [Me2 NH2]Br NH4Br Sr(OH)2(a) KCN < CaBr2 < [Me2NH2]Br < NH4Br < Sr(OH)2 (b) NH4Br < [Me2NH2]Br < CaBr2 < KCN < Sr(OH)2 (c) NH4Br < Sr(OH)2 < KCN < CaBr2 < [Me2NH2]Br (d) [Me2NH2]Br < NH4Br < CaBr2 < KCN < Sr(OH)2 (e) CaBr2 < [Me2NH2]Br < NH4Br < Sr(OH)2 < KCN 10. Which one of the fol owing statements is false? (a) The pH of pure water is greater than 7.0 at 60 ºC. (b) The conjugate base of HCN is CN-.(c) In pure water, pH = pOH. (d) Cu2+ is a Lewis acid. (e) HOF(aq) is a weak acid. 11 . A quantity of NaCN(s) (FW = 49.0 g/mol) was dissolved in water to form 1000 mL of solution. If the pH = 11.09, then how many grams of NaCN were dissolved? (a) 7.8 g (b) 0.40 g (c) 4.5 g (d) 3.1 g (e) 0.012 g 12. What is the equilibrium constant, Kc, for the acid-base reaction shown below? HCN + ClO- CN- + HOCl a) 1.2 x 10-7 (b) 33 (c) 0.021 (d) 4.8 x 108 (e) 50 13. Which one of the following conjugate pairs would be best suited for the formation of a buffer with pH = 6.40? (a) HNO2 / NO2- (b) CH3CO2H / CH3CO2- (c) H2PO4- / HPO42- (d) HOCl / ClO- (e) HPO42- / PO43- 14. A buffer was prepared by dissolving 0.0389 mol pyridinium chloride ([C5H5NH]Cl) and 0.0255 mol NaOH in water to form a solution with a total volume of 475 mL. What is the pH of the solution? (a) 4.99 (b) 6.21 (c) 5.13 (d) 5.04 (e) 5.51 15. To the buffer described in problem 14 is added exactly 20.0 mL 0.0500 M HCl(aq). What is the pH of the final mixture?
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This note was uploaded on 02/26/2008 for the course PHYS 2010 taught by Professor Dubson during the Fall '06 term at Colorado.