Brass is an alloy of copper and zinc. A sample of brass weighing 5.793 g, when treated with excess of dil. H_(2)SO_(4) gave 336mL of hydrogen gas at136.5 K and 785 mm pressure. If thehydrogen gas is collected over water andpressure of water vapour under thegiven conditions is 25 mm, find out thepercentage weight of copper in the alloy.

Brass is an alloy of copper and zinc. A sample of brass weighing 5.793

1.	Brass is an alloy of copper and zinc. A sample of brass weighing 5.793 g, when treated with excess of dil. H_(2)SO_(4) gave 336mL of hydrogen gas at136.5 K and 785 mm pressure. If thehydrogen gas is collected over water andpressure of water vapour under thegiven conditions is 25 mm, find out thepercentage weight of copper in the alloy.
Answer» Solution :AMONG Cu and Zn, only Zn displaces `H_(2)" from "H_(2)SO_(4)` `Zn+H_(2)SO_(4) to ZnSO_(4) + H_(2)` Pressure = 785 - 25 = 760 mm TEMPERATURE = 136.5 K, volume = 336mL `(P_(1)V_(1))/T_(1) = (P_(2)V_(2))/T_(2)` `(760 xx 336)/(136.5) = (760 xx V_(2))/(273)` ` V_(2) = 672` mL `(V_(2))` Vol. of `H_(2)` liberated at STP = 672 mL Weight of zincrequired= `(65.5 xx 672)/(22400) = 1.965` g Weight of copper in brass = `5.793 - 1.965 = 3.828` g % of Cu in the alloy = `(3.828)/(5.793) xx 100 = 66%`