Question

At ${90}^{\circ }C,$ pure water has
$\left[H_3{O}^{+}\right]={10}^{-6}mol{L}^{-1}.$ What is the value of $K_w$ at ${90}^{\circ }C?$

• A. ${10}^{-6}$
• B. ${10}^{-12}$
• C. ${10}^{-14}$
• D. ${10}^{-8}$

Answer 1

The correct option is B ${10}^{-12}$

Irrespective of temperature, hydrogen and hydroxyl ion concentration will be same as they are formed by the ionizaion of water inequal amounts.
$K_w$ is the product of molar concentration of hydrogen and hydroxyl ions in pure water.
For pure water at ${90}^{\circ }C$, $\left[H_3{O}^{+}\right]=\left[O{H}^{-}\right]={10}^{-6}\Rightarrow K_w={10}^{-6}\times {10}^{-6}={10}^{-12}$