Under the action of dilute sulfuric acid on 25 g of a mixture of magnesium and copper, 3.6 liters of gas were released.

Under the action of dilute sulfuric acid on 25 g of a mixture of magnesium and copper, 3.6 liters of gas were released. Calculate the mass fraction of copper in the mixture.

copper will not react with dilute sulfuric acid
Mg + H2SO4 = MgSO4 + H2
n (H2) = 3.36 / 22.4 = 0.15 mol
hence n (Mg) = 0.15 mol
m (Mg) = 0.15 * 24 = 3.6 gr
mass of copper in the mixture = 25-3.6 = 21.4 g
mass fraction of copper = 21.4 / 25 = 0.856
answer 85.6 percent