# Chapter 15 - Solutions of Acids and Bases - Questions and Exercises - Exercises - Page 673: 15.35

$[OH^-] = 2.5 \times 10^{- 7}M$

#### Work Step by Step

1. Use "$K_w$" to calculate the $[OH^-]$ $[H_3O^+] * [OH^-] = Kw = 10^{-14}$ $4 \times 10^{- 8} * [OH^-] = 10^{-14}$ $[OH^-] = \frac{10^{-14}}{ 4 \times 10^{- 8}}$ $[OH^-] = 2.5 \times 10^{- 7}M$

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