32 g of water were evaporated from 72 g of a 5% solution of copper (II) sulfate. Find the mass fraction of salt in the resulting solution.

Given: m (solution) = 72 g,: ω (CuSO4) = 5%, or 0.05, m (H2O) = 32 g.
Find: ωп (CuSO4) -?
Decision.
1. Find the mass of the solute (CuSO4) in the initial solution:
m (CuSO4) = m (solution) • ω (CuSO4) = 72 g • 0.05 = 3.6 g.
2. Find the mass of the new solution:
mn (solution) = m (solution) – m (H2O) = 72 g – 32 g = 40 g.
3. Find the mass fraction of the solute (CuSO4) in the new solution:
ωn (CuSO4) = m (CuSO4) / mn (solution) = 3.6 g: 40 g = 0.09, or 9%.
Answer: 9%.

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