Question

An aqueous solution of hydrogen sulphide shows the equilibrium,

$H_{2}S\rightleftharpoons H^{+}+HS^{-}$

If dilute hydrochloric acid is added to an aqueous solution of hydrogen sulphide without any change in temperature, then

• A. the equilibrium constant will change
• B. the concentration of $HS^{-}$ will increase
• C. the concentration of undissociated hydrogen sulphide will decrease
• D. the concentration of $HS^{-}$ will decrease

Answer 1

Answer: (D)

$K_{a}$ for $H_{2}S=\frac{\left[\right. H^{+} \left]\right. \left[\right. H S^{-} \left]\right.}{\left[\right. H_{2} S \left]\right.}$

Due to common ion effect an increase in $\left[\right.H^{+}\left]\right.$ will show a decrease in $\left[\right.HS^{-}\left]\right.$ as dissociation of $H_{2}S$ will decrease.