When Victoria mixes aqueous solutions of 1.25 L of 0.0500 M Pb(NO3)2 and 2.00 L of 0.0250 M Na2SO4, PbSO4 precipitates. Show your work.

Question

a) Calculate the moles of Pb²⁺ and SO₄^2- ions in the mixed solution.

b) Which ion is limiting?

c) Calculate the moles of PbSO₄ formed. 

d) Calculate the mass of PbSO₄ formed.

Answer 1

Write the balanced equation:

Pb(NO₃)₂(aq) + Na₂SO₄(aq) ==> PbSO₄(s) + 2NaNO₃(aq)

a) moles Pb²⁺ = 1.25 L x 0.0500 mols/L = 0.0625 mols Pb²⁺

moles SO₄^2- = 2.00 L x 0.0250 mols/L = 0.0500 mols SO₄^2-

b) SO₄^2- is limiting since they react in a 1:1 mol ratio, and there are fewer mols of SO₄^2-.

c) moles PbSO₄ formed = 0.0500 mols

d) mass PbSO₄:

molar mass PbSO₄ = 303.3 g/mol

mass PbSO₄ = 0.0500 mols x 303.3 g/mol = 15.2 g (3 sig. figs.)