## General Chemistry (4th Edition)

Published by University Science Books

# Chapter 20 The Properties of Acids and Bases - Problems - Page 770: 15

#### Answer

$[H_3O^+] = 4 \times 10^{- 8}M$ $[OH^-] = 2.5 \times 10^{- 7}M$

#### Work Step by Step

We use the pH to find: $[H_3O^+] = 10^{-pH}$ $[H_3O^+] = 10^{- 7.4}$ $[H_3O^+] = 4 \times 10^{- 8}M$ Using the concentration of $H_3O^+$, we find: $[H_3O^+] * [OH^-] = Kw = 10^{-14}$ $4 \times 10^{- 8} * [OH^-] = 10^{-14}$ $[OH^-] = \frac{10^{-14}}{ 4 \times 10^{- 8}}$ $[OH^-] = 2.5 \times 10^{- 7}M$

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