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)

$6$

Answer 2

${6Fe^{2+} + Cr2 \,O^{2-}_7 + 14H+ -> 6Fe^{3+} + 2Cr^{3+} + 7H_2O}$
Mohr?s salt $\left[FeSO_{4}\cdot \left(NH_{4}\right)_{2}SO_{4}\cdot6H_{2}O\right]$
and dichromate reacts in $6 : 1$ molar ratio.
So, no. of moles of Mohr?s salt $= 6$