Chemistry - Complete P-block Question with Solution | TestHub
When 6.2 g of an impure sample of a white waxy non-metallic solid X is dissolved in boiling caustic soda in an inert atmosphere, a foul-smelling gas is evolved. The gas is passed into aqueous copper sulphate solution, which absorbs it completely as a copper phosphide; 7.155 g of CuSO₄ (M = 159) is required for complete absorption.
If x = percentage purity of X in the sample and y = volume (in mL) of the evolved gas measured at 1 atm and 0 °C, find the value of (x + y). (Impurities do not react with caustic soda.) [H = 1, O = 16, Na = 23, P = 31, S = 32, Cu = 63]
Answer:
Solution:
X = P₄ (white, waxy ; with hot NaOH gives foul-smelling PH₃) : P₄ + 3NaOH + 3H₂O → PH₃ + 3NaH₂PO₂ ; 2PH₃ + 3CuSO₄ → Cu₃P₂ + 3H₂SO₄. n(CuSO₄) = 7.155/159 = 0.045 mol → n(PH₃) = (2/3) × 0.045 = 0.03 mol → y = 0.03 × 22400 = 672 mL. n(P₄) = n(PH₃) = 0.03 mol → mass of P₄ = 0.03 × 124 = 3.72 g → x = (3.72/6.2) × 100 = 60. x + y = 60 + 672 = 732.
