Question

A weak acid react with strong base, ionisation constant of weak acid is 10${}^{-4}$. Find out equilibrium constant for this reaction.

• A. 10${}^{-10}$
• B. 10${}^{10}$
• C. 10${}^{-9}$
• D. 10${}^9$

Answer 1

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

$WA+SB$ $WA⟶HA$ $SB⟶BOH$

Water Dissociation,

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

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

$K_w={10}^{-14}$

$HA\leftrightharpoons H^{+}+A^{-}$

$K_a=\frac{\left[H^{+}\right]\left[A^{-}\right]}{\left[HA\right]}={10}^{-4}$

$HA+O{H}^{-}\leftrightharpoons H_{2}O+A^{-}$

$K=\frac{\left[A^{-}\right]\left[H_{2}O\right]}{\left[HA\right]\left[{OH}^{-}\right]}$

$K=\frac{K_a}{K_w}=\frac{{10}^{-4}}{{10}^{-14}}={10}^{10}$