Question 10.9: Calculating [H3O^+] from pH Determine the [H3O^+] for soluti...
Calculating [ \pmb{H_{3} O^{+}} ] from pH
Determine the \left[H_{3} O^{+}\right] for solutions having each of the following pH values:
a. pH = 3.0
b. pH = 8.25
a. For pH values that are whole numbers, the \left[H_{3} O^{+}\right] can be written 1 \times 10^{-pH}.
\left[H_{3} O^{+}\right] = 1 \times 10^{-3} Mb. For pH values that are not whole numbers, the \left[H_{3} O^{+}\right] is calculated as follows:
Step \fbox{1} State the given and needed quantities.
| ANALYZE THE PROBLEM |
Given | Need | Know |
| pH = 8.25 | \left[H_{3} O^{+}\right] | \left[H_{3} O^{+}\right]=10^{-pH} |
Step \fbox{2} Enter the pH value into the inverse log equation and change the sign.
Procedure Calculator Display
8.25 \fbox{+/–} -8.25
Press the 2nd function key and then the 10^{x} key. Or press the inverse key and then the log key.
2^{nd} 10^{x} or \fbox{inv} \fbox{log} 5.623413252^{- 09} or 5.623413252-09 or 5.623413252E-09
Step \fbox{3} Adjust the SFs in the coefficient. Because the pH value of 8.25 has two digits on the right of the decimal point, the \left[H_{3} O^{+}\right] is written with two significant figures.
\left[H_{3} O^{+}\right]=\underset{\text{Two SFs }}{5.6} \times 10^{-9} MGuide to Calculating [ \pmb{H_{3} O^{+}} ] from pH
Step \fbox{1}
State the given and needed quantities.
Step \fbox{2}
Enter the pH value into the inverse log equation and change the sign.
Step \fbox{3}
Adjust the SFs in the coefficient.