MCAT Chemistry – Acids
- Feb 05, 2015
- MCAT Blog, MCAT Chemistry, MCAT Question of the Day
In the titration of acid HA against the strong base NaOH, which of the following acids will form a neutral solution at the equivalence point?
A) I only
B) I and II only
C) I and III only
D) I, II, and III
This question is testing your understanding of acid-base titrations and the contents of the solution formed at the equivalence point. To answer this question, you must know that at the equivalence point the solution consists of 100% of the conjugate base and water. Therefore, at the equivalence point of HCl, HF, and HI, the solution will contain water and Cl–, F–, and I–, respectively. The conjugate base of a strong acid does not react with water. Therefore, I and III will form a neutral solution. The conjugate base of a weak acid does however react with water to produce the weak acid and hydroxide, as follows:
A– + H2O —> HA + OH–
Hydrofluoric acid is a weak acid despite being a hydrogen halide and therefore will form a basic solution at the equivalence point. Thus, C is the correct answer.
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