`KMnO_4` is prepared from the mineral pyrolusite, `MnO_2` (deep purple colour). It acts as an oxidising agent in the neutral, alkaline as well as acidic medium in acidic medium it is used in volumetric analysis for estimation of `Fe^(2+)`, `Cr_2O_4^(2-)` salts etc. The titrations are carried out in presence of `H_2SO_4`. However, before using it as a titrant, it is first standardised with standard oxalic acid solution or Mohr's salt solution . In one of the experiments on titration 26.8g of dry pure sodium oxalate `(Mw=123gmol^-1)` was dissolved in 1L of distilled water and then 100 mL of `2MH_2SO_4` were added. The solution was cooled. Now to this solution `0.1MKMnO_4` solution was added till a very faint pink colour persisted.
Q. If `0.1MK_2Cr_2O_7` solution were used in place of 0.1 `MKMnO_4` solution used would be

Options

A. 200 mL
B. 400 mL
C. 333.3 mL
D. 666.6 mL

Answer

d

Explanation

First method: `Cr_2O_7^(2-)+14H^(o+)+3C_2O_4^(2-)to2Cr^(3+)+7H_2O+6CO_2` Moles of `K_2Cr_2O_7` required for 0.2 mol of sodium oxalate `=(1)/(3)xx0.2=0.666`.
Hence. Volume of 0.1 M `K_2Cr_2O_7` solution present in
Second Menthod:
mEq.of `Cr_2O_7^(2-)=mEq.C_2O^4^(2-)`
`(0.1Mxx6)NxxV=((26.8)/(134)xx2)xx10^3mEq`.
`0.6VmEq.=400mEq`.
`V=(400)/(0.6)666.6mL`