Question

The degree of ionization of water was found to be $1.8\times {10}^{-9}$. The $K_a$ of water is .....

• A. $1.8\times {10}^{-9}$
• B. $1.8\times {10}^{-16}$
• C. $1\times {10}^{-14}$
• D. Cannot be calculated

Answer 1

Answer: (B)

$1.8\times {10}^{-16}$

Degree of ionization$=1.8\times {10}^{-9}$

$H_{2}O\rightleftharpoons H^{+}+O{H}^{-}$

$k_a=\frac{\left[H^{+}\right]\left[{OH}^{-}\right]}{\left[H_{2}O\right]}$ $55M=\left[H_{2}O\right]$

$=\frac{({10}^{-7}{)}^2}{55}$

$k_a=1.82\times {10}^{-16}$