Question

Which of the following reaction is preferred at anode during the electrolysis of $H _{2} SO _{4}$ at higher concentration?

• A. $2 H _{2} O (l) \longrightarrow O _{2}(g)+4 H ^{+}(a q)+4 e^{-}$
• B. $2 SO _{4}^{2-}(a q) \longrightarrow S _{2} O _{3}^{2-}(a q)+2 e^{-}$
• C. Both (a) and (b)
• D. None of these

Answer 1

Answer: (B)

During the electrolysis of $H _{2} SO _{4}$ (dilute)
$2 H _{2} O (l) \longrightarrow O _{2}(g)+4 H ^{+}(a q)+4 e^{-} ; E_{\text {cell }}^{\circ}=1.23\, V$
During the electrolysis of conc. $H _{2} SO _{4}$
$2 SO _{4}^{2-}(a q) \longrightarrow S _{2} O _{8}^{2-}(a q)+2 e^{-} ; E_{\text {cell }}^{\circ}=1.96\, V$