Calculations with equations involving solutions
4 marks · NormalA reaction between barium chloride and sodium sulfate is shown by the equation:
Calculate the number of moles of Na₂SO₄ in 40 cm³ of solution with concentration 0.10 mol/dm³.
Use the balanced equation to determine the number of moles of BaCl₂ that react with this amount of Na₂SO₄.
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(a) 0.004 mol
(b) 0.004 mol
Common mistakes: Not converting cm³ to dm³; not using 1:1 molar ratio in the equation
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Marking points
M1 (a) · 1 mark · Converts 40 cm³ to 0.040 dm³ or uses the correct formula.
A1 (a) · 1 mark · Correct calculation: 0.004 mol of Na₂SO₄. (follow-through)
M2 (b) · 1 mark · Uses the equation to identify 1:1 reaction ratio. (follow-through)
A2 (b) · 1 mark · Correctly states 0.004 mol of BaCl₂ reacts. (follow-through)
Worked solution
a) Convert 40 cm³ to dm³: 40 ÷ 1000 = 0.040 dm³.
b) Molar ratio of Na₂SO₄ to BaCl₂ is 1:1. Therefore, moles of BaCl₂ = 0.004 mol.