AP®ChemistryCollege BoardExam QuestionsUnit 8: Acids & BasesBuffers

Buffers (College Board AP® Chemistry)

Exam Questions

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Buffers

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Buffers

11 mark

Which statement about buffer solutions is not correct?

  • A buffer resists small changes in pH.

  • A buffer can be formed from sodium hydroxide and an excess of ethanoic acid.

  • The pH during a titration between a strong acid and weak base changes slowly in the buffer region.

  • When a strong acid is added to a buffer, hydrogen ions react with salt ions. 

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21 mark

Which mixture will not act as a buffer?

  • CH3COOH (aq) and CH3COONa (aq) 

  • CH3CH2COOH (aq) and CH3CH2COONa (aq) 

  • HNO3 (aq) and NaOH (aq)

  • NH3 (aq) and NH4Cl (aq) 

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31 mark

A buffer with a pH of 5.00 is needed. Which of the following should be used?

  • Ammonia with a Kb of 1.8 x 10-5.

  • Ethanoic acid with a Ka of 1.8 x 10-5.

  • Carbonic(II) acid with a Ka of 4.7 x 10-11.

  • Nitrous acid with a Ka of 4.0 x 10-4.

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41 mark

A buffer at pH 4.40 is prepared from a weak acid with a pKa = 4.60. If 50 mL of this buffer is dilited to 100 mL with distilled water, what is the pH of the dilute solution?

  • 5.40

  • 4.50

  • 4.60

  • 4.40

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51 mark

The weak acid CH3COOH has a pKa of 4.76.

A solution is prepared by mixing 250 mL of 0.200 M CH3COOH (aq) and 0.8 g of NaOH (s).

Which of the following can be used to calculate the pH of the solution?

  • pH = 4.76 + log10 fraction numerator stretchy left square bracket 0.03 stretchy right square bracket over denominator stretchy left square bracket 0.02 stretchy right square bracket end fraction = 4.93

  • pH = 4.76 + log10 fraction numerator stretchy left square bracket 0.08 stretchy right square bracket over denominator stretchy left square bracket 0.02 stretchy right square bracket end fraction = 6.36

  • pH = 4.76 + log10 fraction numerator stretchy left square bracket 0.02 stretchy right square bracket over denominator stretchy left square bracket 0.03 stretchy right square bracket end fraction = 4.58

  • pH = 4.76 + log10 fraction numerator stretchy left square bracket 0.02 stretchy right square bracket over denominator stretchy left square bracket 0.05 stretchy right square bracket end fraction = 4.36

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