exam3 - Version 315 – Exam 3 – Sutcliffe –(52440 1...

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Unformatted text preview: Version 315 – Exam 3 – Sutcliffe – (52440) 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points K sp for CaF 2 is 3 . 9 × 10- 11 . Would a pre- cipitate of CaF 2 form if Ca(NO 3 ) 2 and NaF solutions were mixed such that [Ca 2+ ] = 2 . × 10- 4 M, and [F- ] = 3 . × 10- 4 M? 1. no correct 2. yes, because Q is larger than K sp 3. yes, because Q is smaller than K sp Explanation: 002 10.0 points NOTE: ”Ionization constant” here means ”K a ”. What would be the final pH if 0.0100 moles of solid NaOH were added to 100 mL of a buffer solution containing 0.600 molar formic acid (ionization constant = 1 . 8 × 10- 4 ) and 0.300 molar sodium formate? 1. 3.44 2. 4.05 3. 3.65 correct 4. 3.84 5. None of these Explanation: 003 10.0 points The volume of 0.100 M NaOH required for the titration of 100 mL of 0.100 M CH 3 COOH to the equivalence point would be (larger than, the same as, smaller than) if the acid were 100 mL of 0.100 M HCl. The equivalence point for the HCl titration would come at (a higher, a lower, the same) pH than for the CH 3 COOH titration. 1. smaller than; the same 2. larger than; a lower 3. the same; a lower correct 4. larger than; a higher 5. the same as; a higher Explanation: [NaOH] = 0.1 M [CH 3 COOH] = 0.1 M [HCl] = 0.1 M V HCl = 100 mL V CH 3 COOH = 100 mL The amount of acid required to react a given number of moles of base depends on the total number of moles of H 3 O + the acid can provide. 100 mL of 0.1 M CH 3 COOH and 100 mL of 0.1 M HCl both provide 10.0 mmol H 3 O + . However, because CH 3 COOH is a weak acid and HCl is a strong acid the pH at the equivalence points will differ. In the case of HCl the spectator ions present do not hydrolyze and the endpoint pH is 7. In the case of CH 3 COOH, the CH 3 COO- tritra- tion product hydrolyzes, producing OH- ions which raise the pH above 7. 004 10.0 points Which one of the following combinations can produce a buffer solution? 1. HCl and NaCl 2. HBr and NaBr 3. HI and NaI 4. HF and NaF correct 5. HNO 3 and NaNO 3 Explanation: A buffer must contain a weak acid/base conjugate pair. HI / I- , HCl / Cl- , HBr / Br- and HNO 3 / NO- 3 are strong acid/base con- jugate pairs. HF / F- is a weak acid/base conjugate pair. 005 10.0 points Version 315 – Exam 3 – Sutcliffe – (52440) 2 In human blood carbonic acid and the bicar- bonate ion act as one of the buffer systems that maintains the pH of blood at 7.40. What molar ratio of HCO- 3 to H 2 CO 3 is needed? ( K a = 4 . 2 × 10- 7 for carbonic acid.) 1. HCO- 3 H 2 CO 3 = 8 1 2. HCO- 3 H 2 CO 3 = 3 10 3. HCO- 3 H 2 CO 3 = 20 1 4....
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exam3 - Version 315 – Exam 3 – Sutcliffe –(52440 1...

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