How do you go about figuring out this questions?

Question

A mixture contained zinc sulfide, ZnS, and lead sulfide, PbS. A sample of the mixture weighing 6.17 g was reacted with an excess of hydrochloric acid. The reactions are


ZnS(s) + 2HCl(aq) ==> ZnCl2(aq) + H2S(g)

PbS(s) + 2HCl(aq) ==> PbCl2(aq) + H2S(g)


If the sample reacted completely and produced 1.051 L of hydrogen sulfide, H2S, at 23oC and 745 mmHg, what were the percentages of ZnS and PbS in the mixture.

Answer 1

too easy,

first apply the ideal gas law to find the moles of H2S

then

moles of hydrogen sulfide=moles ofZnS + moles of PbS

Now

(moles of ZnS)*(molecular weight of ZnS)+(moles of PbS)*(molecular weight of PbS) = 6.17g

The molecular weights can be found in any chemistry textbook

So there you have it, a two equation and two variable system, which can be easily solved by elemmentary algebra.

Cheers