Question

A 0.5 g sample of an iron-containing mineral mainly in the form of CuFeS₂ was reduced suitably to convert all the ferric iron into ferrous form and was obtained as a solution. In the absence of any interfering matter, the solution required 42 ml of 0.01 M K₂Cr₂O₇ solution for titration. The percentage of CuFeS₂ in the mineral is ______%.
(Cu = 63.5, Fe = 55.8, S = 32, O = 16)

Options

• 91.60

• 92.40

• 93.50

• 94.30

Answer 1

A 0.5 g sample of an iron-containing mineral mainly in the form of CuFeS₂ was reduced suitably to convert all the ferric iron into ferrous form and was obtained as a solution. In the absence of any interfering matter, the solution required 42 ml of 0.01 M K₂Cr₂O₇ solution for titration. The percentage of CuFeS₂ in the mineral is 92.40%.

Explanation:

Let the weight of CuFeS₂ in the 0.5 g of mineral be x.

Then the eq. of CuFeS₂ = Eq. of K₂Cr₂O₇

⇒ = `"x"/(183.3//1)` = (0.01 × 6) × (42 × 10^–3)

⇒ x = 0.462

∴ % of CuFeS₂ in mineral = `0.462/0.5 × 100` = 92.4%