A sample of chromium containing alloy weighing 3.45 g was dissolved in acid and all chromium was oxidised to `CrO_(4)^(2-)`. 3.15g of `Na_(2) SO_(3)` was required to reduce the `CrO_(4)^(2-)` to `CrO_(2)`, in a basic solution while so ion being oxidised to `SO_(4)^(2-)`. Calculate mass % of chromium in sample. [Molar mass of Cr=52]

Options

A. `25.13%`
B. `76.3%`
C. `80%`
D. `10%`

Answer

A

Explanation

Gram equivalent of `Na_(2)SO_(3)` used up `=(3.15)/(63)=50xx10^(-3)`
Moles of
`CrO_(4)^(2-)=(50xx10^(-3))/(3)=16.67xx10^(-3)` moles of Cr

Mass of `Cr=16.67xx10^(-3)xx52=0.867g`
% Cr is sample `=(0.867)/(3.45)xx100=25.13%`