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

Options

A. 3
B. 4
C. 5
D. 6

Answer

D

Explanation

Mohr's salt `(FeSO_(4).(NH_(4))_(2)SO_(4).6H_(2)O_(2))` is a reducing agent involving one `e^(-)` change while `K_(2)Cr_(2)O_(7)` is an oxidising agent involving six `e^(-)` change
`{:(Fe^(2+)rarrFe^(3+)+e^(-)"]"xx6),(Cr_(2)O_(7)^(2-)+14H^(+)+6e^(-)rarr2Cr^(3+)+7H_(2)O),(ulbar(6Fe^(2+)+Cr_(2)O_(7)^(2-)+14H^(+)rarr6Fe^(3+)+2Cr^(3+)+7H_(2)O)):}`
Thus, 1 mole of `Cr_(2)O_(7)^(2-)` ion will oxidise 6 moles of Mohr's salt.