Question

Consider a titration of potassium dichromate with acidified Mohr’s salt solution using diphenylamine as indicator. The number of moles of Mohr’s salt required per mole of dichromate is :

• A. 3
• B. 4
• C. 5
• D. 6

Answer 1

Answer: (D)

$n$-factor of dichromate is $6$ .
Also, $n$-factor of Mohr's salt is $1$ as :
$\underset{\text{ Mohr’s salt }}{FeS{O}_4{\left(N{H}_4\right)}_{2}S{O}_4}\cdot 6H_{2}O\stackrel{O.A}{\to }F{e}^{3+}$
$\because 1$ mole of dichromate $=6$ equivalent of dichromate.
$\therefore 6$ equivalent of Mohr's salt would be required.
Since, $n$-factor of Mohr's salt is $1,6$ equivalent of it would also be equal to $6$ moles.
Hence, $1$ mole of dichromate will oxidise $6$ moles of Mohr's salt.