You add Na2S to water containing Cu(2+)-ions and SO4(2-) ions. The net equation will therefore be:
Na2S + Cu(2+) --> Na(+) + CuS
Now you have the stoichiometry and you have to convert the mass of CuS to mol. Use the stoichiometry to find the amount of Cu(2+) that is needed to form 0,0177 g CuS.
The calculate molarity with c = n/V.
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