Consider the titraton of potassium dichromate solution with acidfied mohr salt solution using dmiethylamine as incdicator the number of moles of mohr salt required per mole of dichromate

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]` is a reducing agent involving 1`e^(-)` change while `K_(2)Cr_(2)O_(7)` is an oxidising agent invoving 6 `e^(-)` change i.e
`Fe^(2+)rarrFe^(3+)+e^(-)]xx6`
`Cr_(2)O_(7)^(-)+14H^(+)+6e^(-)rarr2Cr^(3+)+7H_(2)O`
`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