Calculating pH Using the [OH^{-}]
What is the pH of an ammonia solution with [OH^{-}]=3.7 ×10^{-3} M?
Step 1 Enter the [H_{3}O^{+}]. Because [OH^{-}] is given for the ammonia solution, we have to calculate [H_{3}O^{+}] using the K_{w} .When we divide through by the [OH^{-}] ,we obtain the [H_{3}O^{+}].
\frac{K_{w}}{[OH^{-}]}=\frac{[H_{3}O^{+}] \cancel{[OH^{-}]}}{\cancel{[OH^{-}]}}[H_{3}O^{+}]=\frac{1.0 ×10^{-14 } }{[3.7 ×10^{-3} ]}=2.7 ×10^{-12} M
Step 2 Press the log key and change the sign.
\boxed{log} \boxed{+/-} 11.56863
Step 3 Adjust the number of SFs on the right of the decimal point to equal the SFs in the coefficient.