0.10 g of a sample containing CuCO ₃ and some inert impurity was dissolved in dilute sulphuric acid and volume made up to 50 ml . This solution was added into 50 ml of 0.04 M KI solution where copper precipitates as Cul ⁻¹ I ⁻ is oxidised i

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0.10 g of a sample containing CuCO ₃ and some inert impurity was dissolved in dilute sulphuric acid and volume made up to 50 ml . This solution was added into 50 ml of 0.04 M KI solution where copper precipitates as Cul ⁻¹ I ⁻ is oxidised into I ₃⁻ . A 10 ml portion of this solution is taken for analysis filtered and made up free I₃⁻ and then treated with excess of acidic permanganate solution. Liberated iodine requi

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Correct answer: B. 74.1

m moles of KI =50 0.04=2 m.eq. of Na ₂ ~S ₂ O ₃ reacted with 10 ml solution =20 2.5 10⁻³=50 10⁻³ m.eq. of I' left unreacted in 100 ml solution =50 10⁻³ 100 10 =0.5 m . moles of I reacted with CuCO ₃=2-0.5=1.5 2 Cu ⁺⁺+5 I ⁻ 2 CuI + I ₃⁻ m.moles of Cu ⁺⁺= 2 5 1.5=0.6 wt. of CuCO ₃=0.6 10⁻³ 123.5=0.0741 wt. of CuCO ₃= 0.0741 0.1 100=74.1

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