Copper (II) oxide weighing 38 g can react with 154 g of hydrochloric acid solution. Determine the mass fraction of acid in the solution.

1) Let’s compose the reaction equation:
СuO + 2HCl = CuCl2 + H2O
2) Calculate the amount of copper (II) oxide substance:
n (CuO) = m (CuO) / M (CuO) = 38/80 = 0.475 mol.
3) Determine the amount of substance, the mass of hydrochloric acid and its mass fraction in the solution:
n (HCl) = 2n (CuO) = 2 ∙ 0.475 = 0.95 mol
m (HCl) = n (HC) ∙ M (HC) = 0.95 ∙ 36.5 = 34.675 g.
ω (HCl) = (m (HCl) / m (solution)) ∙ 100% = (34.675 / 154) ∙ 100 = 22.52%
Answer: 22.52%.