Question

For the precipitation of cations of group four in the qualitative analysis, the medium is made alkaline before passing $H_2S$ gas. The purpose of alkaline solution is

• A. to supress the ionisation of $H_2S$
• B. to increase the ionisation of $H_2S$
• C. to increase die ionisation of metal salt
• D. to decrease die ionisation of metal salt

Answer 1

Answer: (B)

$H_{2}S \rightleftharpoons 2H^{+}+S^{-2}$
$NH_{4}OH \to NH^{+}_{4}+OH^{-}$
$H^{+}$ combines with $OH^{-}$ to form water and thus the first equilibrium shifts in the forward direction to increase the ionisation of $H_{2}S$