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

Answer

C

Explanation

During the reaction, following changes take place :
`overset(+6)(C)r_(2)O_(7)^(2-) rarr 2 overset(+3)(C)r^(3+)`
`underset("(From Mohr's salt)")overset(+2)(Fe^(2+))rarr overset(+3)(F)e^(3+)`
Since the oxidation number of Cr decreases from ` + 12` (for two Cr atoms ) to `+6`, onr molr of ` K_2CrO_7` contains ix equiva-lents. In Mohr's salt, the oxidation number of iorn increases from ` +2 ` to ` +3`. Thus, on mole of Mohr's salt contains just one equivalent, According to the law of equivalents, we need six equivalents (six moles) of mohr's salt to reduce one mole of ` K_2CrO_7`.