A mass of 2.72 g of an alloy containing Pb, required for dissolved in `HNO_3` containing `50%` by mass of `HNO_3`. When a `H_(2)SO_(4)` solution was added, 1.5 g of precipitate (A) appeared `H_(2)S` gas was then passed into the remaining solution a secfond precipitate was formed which when calcined in air produced 1.6 g of a compound B. Determine the composition of an alloy. (Al does not form `Al_(2)S_(3)` due to the hydrolysis of sulphide).

Explanation

`Al,Pb,Cuoverset(H_(2)SO_(4))toPbSO_(4)`
`underset(1 mol)(Pb)overset(HNO(3))toPb(NO_(3))_(2)overset(H_(2)SO_(4))toPbSO_(4)`
Mass of Pb on passing `H_(2)S=(1.5)/(304)xx208=1.026`g
`CuS(B)overset(O_(2))toCuO`
`1 mol Cu=1 " mol of "CuS-=1 " mol of "CuO`
Mass of `Cu=(1.6)/(79.5)xx63.5=1.278g`
Mass of `Al=2.72-(1.026+1.278)=0.393g`
`% of Pb=37.83`
`% of Cu=46.98`
`% of Al=15.91`