Question

Consider a titration of ${K_2Cr_2O_7}$ solution with acidified Mohr?? salt solution using diphenylamine as indicator. The number of moles of Mohr?? salt required per mole of dichromate is

• A. 3
• B. 4
• C. 5
• D. 6

Answer 1

Answer: (D)

6

Answer 2

The formula of Mohr's salt is $FeSO _{4}\left( NH _{4}\right)_{2} SO _{4}$. It is a mixture of ferrous sulfate and ammonium sulfate. Ferrous sulfate is oxidized by potassium dichromate. The reaction is as follows: $K _{2} Cr _{2} O _{7}+6 FeSO _{4}+7 H _{2} SO _{4} \rightarrow K _{2} SO _{4}+ Cr _{2}\left( SO _{4}\right)_{3}+3 Fe _{2}\left( SO _{4}\right)_{3}+7 H _{2} O$ 1 mole of potassium dichromate reacts with 6 moles of ferrous sulphate. Thus, the number of moles of Mohr's salt required per mole of dichromate is 6 .