Acids & Bases Problem Set

Acids & Bases Problem Set

Question 8: Neutralizing an acidic solution

Tutorial to help answer the question

How many ml of a 0.2 M NaOH solution are required to bring the pH of 20 ml of a 0.4 M HCl solution to 7.0?

A. 4

B. 40

C. 10

D. 20

E. 5

Tutorial

Neutralizing an acidic solution

This question is similar to the previous one. It does not require any complicated calculations, but rather can be solved by considering how acids and bases work.

To begin with, NaOH and HCl both completely dissociate in water, therefore no pK_a calculation is necessary. The implications of this are that a given amount of acid solution has the same number of free protons as the same amount of the same concentration of a base solution.

In this case, the concentration of the acid solution (at 0.4 M) is twice that of the base solution (at 0.2 M). Thus, a neutral pH can be achieved by adding twice the amount of base solution to the acid.

The Biology Project
Department of Biochemistry and Molecular Biophysics
The University of Arizona
January 6, 1999
Revised: October 2004
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