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An amount of 20 g of cooper (II) oxide was treated with a stoichiometric amount of a warm 20% sulphuric acid solution to produce a solution of copper (II) sulphate.
How many grams of crystalline copper(II) sulphate (CuSO4 . 5 H2O) have crystallised when the solution is cooled to 20 °C?
Relative atomic masses: Ar(Cu) = 63.5; Ar(S) = 32; Ar(O) = 16; Ar(H) = 1
Solubility of CuSO4 at 20 oC: s = 20.9 g of CuSO4 in 100 g of H2O.
An amount of 20 g of cooper (II) oxide was treated with a stoichiometric amount of a warm 20% sulphuric acid solution to produce a solution of copper (II) sulphate.
How many grams of crystalline copper(II) sulphate (CuSO4 . 5 H2O) have crystallised when the solution is cooled to 20 °C?
Relative atomic masses: Ar(Cu) = 63.5; Ar(S) = 32; Ar(O) = 16; Ar(H) = 1
Solubility of CuSO4 at 20 oC: s = 20.9 g of CuSO4 in 100 g of H2O.
CuO + H2SO4 → CuSO4 + H2O
n(CuO) = m(CuO)/M(CuO) = 20 g/79.5 g mol-1 = 0.2516 g
n(H2SO4) = n(CuSO4) = 0.2516 mol
Mass of the CuSO4 solution obtained by the reaction:
m(solution CuSO4) = m(CuO) + m(solution H2SO4) =
= m(CuO) + n(H2SO4) x M(H2SO4)/w(H2SO4)
= 20 g + 0.2516 mol 98 g mo-1/ 0.20
m(solution CuSO4) = 143.28 g
Mass fraction of CuSO4:
(a) in the solution obtained:
w(CuSO4) = m(CuSO4)/m(solution CuSO4)
= n(CuSO ) (CuSO )/(solution CuSO4) = 028
(b) in saturated solution of CuSO4 at 20°C:
w(CuSO4) = 209 g/120.9 g = 0.173
(c) in crystalline CuSO4 . 5 H2O:
w(CuSO4) = M(CuSO4)/M (CuSO4.5H2O) =0.639
Mass balance equation for CuSO4:
0.28 m = 0.639 m1 + 0.173 m2
m – mass of the CuSO4 solution obtained by the reaction at a higher temperature.
m1 – mass of the crystalline CuSO4 .5H2O.
m2 – mass of the saturated solution of CuSO4 at 20 °C.
0.28 × 143.28 = 0.639 m1 + 0.173 × (143.28 – m1)
m1 = 32.9 g
The yield of the crystallisation is 32.9 g of CuSO4 . 5H2O.