Reversing the calculations
2 marks · NormalSodium carbonate solution reacts with hydrochloric acid:
Calculate the volume (in cm³) of 0.200 mol/dm³ sodium carbonate solution required to completely react with 30.0 cm³ of 0.400 mol/dm³ hydrochloric acid.
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The required volume of sodium carbonate solution is 30.0 cm³.
Also accept: 30 cm³
Common mistakes: 100 cm³ (incorrect ratio); 60 cm³ (incorrect stoichiometry)
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Marking points
M1 · 1 mark · Correct method: calculates moles of HCl and applies stoichiometry to find moles Na2CO3 needed.
A1 · 1 mark · Correct final calculated volume in cm³ (30.0 cm³).
Worked solution
First, calculate moles of HCl:
From the equation, 2 mol HCl reacts with 1 mol Na2CO3:
Volume of sodium carbonate solution needed: