The number of moles of Na2SO4 form from 4.0 moles Na2S is 4 moles.
Limiting reactants are those reactants that are completely used up in a chemical reaction.
4.0 mol Na2S will be completely used since the combining ratio is 1 : 1 : 1.
Na₂S + CuSO4 ->Na₂SO4 + CuS
From chemical equation above, 4.0 moles Na2S will yield 4 moles of Na₂SO4.
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