Question

What is the product of $H^{+}$ and $O{H}^{-}$ ion's concentration at room temperature?

• A. ${10}^{-14}$
• B. ${10}^{-12}$
• C. $2\times {10}^{-6}$
• D. $2\times {10}^{-7}$

Answer 1

The correct option is A ${10}^{-14}$

Pure water contains ions. There is self-ionisation constant of water, $K_w$, which has no units. It is the product of hydronium ions times the hydroxide ions,

$K_w=\left[H_3{O}^{+}\right]\left[{OH}^{-}\right]$

the ions are equal in concentrations, which experiments have shown to be $1.0\times {10}^{-7}$ for each one at ${25}^{0}C$

$\Rightarrow K_w=\left({10}^{-7}\right)\left({10}^{-7}\right)$

$K_w=1.0\times {10}^{-14}$

$\Rightarrow$ at ${25}^{0}C$, the dissociation constant for pure water is given by $1.0\times {10}^{-14}$.