Answer to Question #306399 in General Chemistry for Andrew

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 $=100-8.02$

$=91.98\%$