Question

Commercial brass, an alloy of Zn and Cu, reacts with hydrochloric acid to form zinc chloride and hydrogen gas. Copper does not react with HCl. When 0.6503 g of a brass sample is reacted with excess HCl, 0.1087 g ZnCl2 is eventually isolated. What is the percent (%) composition of brass by mass?

Answer 1

Zn_(s)$+$ 2HCl_(aq)$\to$ ZnCl_2(aq)$+$ H_2(g)

Moles of ZnCl₂ $=\frac{0.1087}{136.286}$

$=7.976×10^{-4}$ Moles

Mass of Zn $=7.976×10^{-4}×65.38$

$=0.05215g$

$\%$ of Zn $=\frac{0.05215}{0.6503}=8.02\%$

$\%$ of Cu $=100-8.02$

$=91.98\%$