MCAT General Chemistry Question 234: Answer and Explanation

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Question: 234

3. A graph depicting a titration of a weak acid with a strong base will start at a:

  • A. high pH and slope downwards with an equivalence pH equal to 7.
  • B. high pH and slope downwards with an equivalence pH below 7.
  • C. low pH and slope upwards with an equivalence pH equal to 7.
  • D. low pH and slope upwards with an equivalence pH above 7.

Correct Answer: D

Explanation:

D A graph showing the titration of a weak acid will start at a low pH and slope upwards as the titrant (in this case a strong base) is added. Therefore, choices A and B cannot be true. As the weak acid and titrant (strong base) react, water and salt are formed as products. The salt will determine the pH at the equivalence point. The conjugate acid of a strong base has no acidic properties and will be neutral in solution. However, the conjugate base of the weak acid will be weakly basic. Because of this, the pH at the equivalence point will be above 7.

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