# Chapter 15 - Additional Aqueous Equilibria - Questions for Review and Thought - Topical Questions - Page 693a: 19b

Acetic acid and acetate ion are capable of making a buffer with $3.31 \times 10^{-6}M$ of $[H_3O^+]$. This happens because the Ka value for acetic acid is close to this hydronium ion concentration value.

#### Work Step by Step

1. Analyze the $[H_3O^+](3.31 \times 10^{-6}M)$, and find the conjugate acid-base pair with the closest $K_a$ value. - Use Table 15-1 on page 659. - Acetic acid and acetate ion: Ka = $1.8 \times 10^{-5}$ Therefore, this is the best pair that can be used to make a buffer with hydronium ion concentration equal to $3.31 \times 10^{-6}$

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