## Q. 15.5

The concentration of $H_{3}O^{+}$ ions in a sample of lemon juice is $2.5\times 10^{-3} M$. Calculate the concentration of $OH^{-}$ ions, and classify the solution as acidic, neutral, or basic.

STRATEGY

When $[H_{3}O^{+}]$ is known, the $OH^{-}$ concentration can be found from the expression $[OH^{-}] = K_{w}/[H_{3}O^{+}]$.

 IDENTIFY Known Unknown $K_{w}=1.0\times 10^{-14}$ $[OH^{-}]$ $[H_{3}O^{+}]=2.5\times 10^{-3} M$

## Verified Solution

$[OH^{-}]=\frac{K_{w}}{[H_{3}O^{+}]}=\frac{1.0\times10^{-14}}{2.5\times10^{-3}}=4.0\times10^{-12} M$

$Because [H_{3}O^{+}]>[OH^{-}]$, the solution is acidic.