When 4 gm of a impure sample of waxy white non metallic solid X dissolved in boiling caustic soda in inert environment gives a foul smell gas. Foul smell gas require 4.77 gm of copper sulphate from aq

Question

When 4 gm of a impure sample of waxy white non metallic solid X dissolved in boiling caustic soda in inert environment gives a foul smell gas. Foul smell gas require 4.77 gm of copper sulphate from aq. solution for complete absorbtion.

Calculate the percentage purity of given non metallic solid X.

(Impurities show no reaction with caustic soda)

[Given : Atomic mass of H = 1, O = 16, Na = 23, P = 31, S = 32, Cu = 63]

TestHub · Accepted Answer

The waxy white non-metallic solid X is white phosphorus (P₄).

Reaction 1: P₄ + 3NaOH + 3H₂O $\to$ PH₃ + 3NaH₂PO₂

Reaction 2: 2PH₃ + 3CuSO₄ $\to$ Cu₃P₂ + 3H₂SO₄

Molar mass of P₄ = $4 \times 31 = 124$ g/mol

Molar mass of CuSO₄ = $63 + 32 + 4 \times 16 = 159$ g/mol

From Reaction 2, 2 moles of PH₃ react with 3 moles of CuSO₄.

Moles of CuSO₄ = $\frac{4.77 g}{159 g / m o l} = 0.03$ mol

Moles of PH₃ = $\frac{2}{3} \times m o l eso f C u S O_{4} = \frac{2}{3} \times 0.03 = 0.02$ mol

From Reaction 1, 1 mole of P₄ produces 1 mole of PH₃.

Moles of P₄ = moles of PH₃ = $0.02$ mol

Mass of P₄ = $0.02 m o l \times 124 g / m o l = 2.48$ g

Percentage purity = $\frac{M a sso f p u re P _{4}}{T o t a l ma sso f im p u res am pl e} \times 100$

Percentage purity = $\frac{2.48 g}{4 g} \times 100 = 62%$

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JEE Advanced 2027 (Class 12)