The standard calculation
2 marks · HardA student is titrating calcium hydroxide solution with hydrochloric acid. The balanced chemical equation for the reaction is:
Use the balanced equation to state the mole ratio of calcium hydroxide to hydrochloric acid and explain how this ratio is used in a titration calculation.
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.
Show answer
1 mol of Ca(OH)2 reacts with 2 mol of HCl; the ratio is 1:2. This mole ratio is used to convert moles of one substance to moles of the other during titration calculations.
Also accept: The ratio of Ca(OH)2 to HCl is 1:2. For every 1 mole of Ca(OH)2, 2 moles of HCl are needed. This is used to calculate the moles of acid or base that react in the titration calculation.
Common mistakes: Stating 1:1 instead of 1:2; Not explaining how the ratio is used
Show mark scheme and worked solution
Marking points
B1 · 1 mark · Correctly states the mole ratio: 1 Ca(OH)2 : 2 HCl.
B2 · 1 mark · States that this ratio is used in the calculation to relate moles of one reactant to moles of the other during titration.
Worked solution
From the balanced equation, 1 mol of reacts with 2 mol of . The ratio is 1:2. In a titration, this ratio is used to determine how many moles of acid will neutralise a given amount of base (or vice versa) by multiplying or dividing by the stoichiometric coefficients from the balanced equation.