Question

Iodimetric titrations are usually performed in neutral or mildly alkaline $\left(p H \, = \, 8\right)$ or weakly acidic solutions. Which statement is not valid for this observation?

• A. In strong alkaline solution, $I_{2}$ disproportionate to $I^{-}$ and $I O^{-}$
• B. In strong acidic solutions, starch used to detect the end point tends to hydrolyse or decompose
• C. $I^{-}$ produced during titration tends to be oxidised by dissolved oxygen in acidic medium
• D. Reducing power of reducing agent is increased in strong acidic medium

Answer 1

Answer: (D)

$I_{2} \, + \, 2O H^{-} \, \rightarrow I O^{-} \, + \, I^{-} \, + \, H_{2}O$

$H_{2}A s O_{3} \, + \, I_{2} \, + \, H_{2}O \rightarrow \, H_{3}A s O_{3} \, + \, 2I^{-} \, + \, 2H^{+}$

(In acidic medium reverse reaction predominates)

$4I^{-} \, + \, O_{2} \, + \, 4H^{+} \, \rightarrow \, 2I_{2} \, + \, 2H_{2}O$