Question

Compute the $pH$ of a solution at ${25}^{o}C$ (to the nearest integer) which is twice as alkaline as pure water.

Answer 1

The solution is twice as alkaline as pure water.
For pure water, the hydroxide ion concentration is $1\times {10}^{-7}$
M. Hence, the hydroxide ion concentration of the solution is $2\times {10}^{-7}$.
Calculate the pOH of the solution.
$pOH=-log\left[O{H}^{-}\right]=-log(2\times {10}^{-7})=6.7$
Now calculate the pH of the solution.
$pH=14-pOH=14-6.7=7.3$