Question

What is the pH of the solution which is twice alkaline as that of pure water at ${25}^{\circ }C$ ?

• A. 4.3
• B. 7.3
• C. 8.9
• D. 12.6

Answer 1

The correct option is B

7.3

pH = pOH = 7 for pure water

[$O{H}^{-}$] = $1\times {10}^{-7}$
double the conc. of [$O{H}^{-}$] = $2\times {10}^{-7}$

now,

[$O{H}^{-}$] = $2\times {10}^{-7}$
pOH = - log($2\times {10}^{-7}$) = 6.6990

pH = 14.0 = 14.0 - 6.6990 = 7.3010