## Q. 15.7

Acid rain is a matter of serious concern because most species of fish die in waters having a pH lower than 4.5 – 5.0. Calculate the $H_{3}O^{+}$ concentration in a lake that has a pH of 4.5.

STRATEGY

Calculate the $H_{3}O^{+}$ concentration by taking the antilogarithm of the negative of the pH.

 IDENTIFY Known Unknown pH = 4.5 $[H_{3}O^{+}]$

## Verified Solution

$[H_{3}O^{+}]= antilog (-pH)=10^{-pH}=10^{-4.5}=3\times 10^{-5} M$

$[H_{3}O^{+}]$ is reported to only one significant figure because the pH has only one digit beyond the decimal point. (If you need help in finding the antilog of a number, see Appendix A.2.)