Calculations with equations involving solutions
3 marks · EasyZinc sulfate can be made by reacting zinc oxide with sulfuric acid as follows:
25 cm³ of 0.20 mol/dm³ sulfuric acid is used in the reaction. Calculate the number of moles of sulfuric acid used.
How many moles of zinc sulfate could be formed from this amount of sulfuric acid?
Calculate the maximum mass of zinc sulfate, ZnSO₄ (Mᵣ = 161), formed.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) 0.005 mol
(b) 0.005 mol
(c) 0.81 g
Common mistakes: Forgetting to convert cm³ to dm³; Incorrect mole ratio; Calculation mistakes
Show mark scheme and worked solution
Marking points
M1 (a) · 0.5 marks · Converts 25 cm³ to 0.025 dm³
A1 (a) · 0.5 marks · Correct calculation of number of moles of sulfuric acid (follow-through)
B1 (b) · 1 mark · Correct use of 1:1 mole ratio for sulfuric acid to zinc sulfate (follow-through)
M2 (c) · 0.5 marks · Method for finding mass using calculated moles × Mr (follow-through)
A2 (c) · 0.5 marks · Correct answer for mass of zinc sulfate, with working (follow-through)
Worked solution
a) Convert 25 cm³ to dm³: 25 / 1000 = 0.025 dm³
b) Equation shows 1 mol H₂SO₄ gives 1 mol ZnSO₄, so moles of ZnSO₄ = 0.005 mol.
c) Mass = moles × Mr = 0.005 × 161 = 0.805 g (to 2 significant figures: 0.81 g)