AP-style-questions-unit-8 Page 2

Question 6:

Which of the following mixtures would result in a buffer solution?

A) HCl and NaOH B) NH₃ and NH₄Cl C) NaOH and NaCl D) HNO₃ and KNO₃

Question 7:

What happens to the pH of a buffer solution when a small amount of strong acid is added?

A) It increases dramatically B) It decreases dramatically C) It remains completely unchanged D) It decreases slightly

Question 8:

A buffer is made using acetic acid (CH₃COOH) and sodium acetate (CH₃COONa). Which of the following changes will increase the buffer's pH?

A) Adding more CH₃COOH B) Adding more CH₃COONa C) Adding water D) Removing CH₃COONa

Question 9:

Which of the following best describes the action of a buffer?

A) A solution that accelerates reactions B) A solution that neutralizes both acids and bases C) A solution that changes color when pH changes D) A solution that keeps the pH constant no matter what is added

Question 10:

What is the main role of the conjugate base in a buffer solution?

A) To react with added base B) To neutralize water molecules C) To react with added acid D) To make the solution more acidic

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(D) In solution only conjugate acid–base pairs exist. The oxalate ion and oxalic acid differ by more than one H+. The ions of sodium sulfate (response (C)) can exist in solution together.

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(C) The solution contains 0.100 mol of H3PO4, and the addition of 0.250 mol of NaOH represents 2.5 mol base for each mole of phosphoric acid. The first 2 mol of base convert the H3PO4 to . The next 0.5 mol of base converts only half of the  to , and the resulting solution is a mixture of these two ions.

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(B) We need a weak acid with a pKa within 1 pH unit of 10.00 or a weak base with a pKb within 1 pH unit of 4.00 (pOH). Ammonia comes closest to these requirements.

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(A) When the concentrations of the conjugate acid and base are equal, pH = pKa.

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(B) The Kb is

The pH is given as 10.45, and so the pOH is 3.55. We can