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MCAT Chemistry – Acids

  • by Kerry Goldstein
  • 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?

I. HCl

II. HF

III. HI

 

A) I only

B) I and II only

C) I and III only

D) I, II, and III

 

 

Explanation

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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