Reversing the calculations

3 marks · Normal

Explain, step by step, how you would calculate the required volume of one solution needed to react completely with a known amount of another reactant, using their concentrations and the chemical equation. Include the reason for each step.

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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Must show: Clear steps, Reason for each step

Common mistakes: Omitting unit conversions; Skipping explanation for steps

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Marking points

B1 · 1 mark · Explains calculating moles of the known reactant using its concentration and volume, including reason.

B2 · 1 mark · Describes using the balanced chemical equation to find moles of the other reactant (stoichiometry), including reason.

B3 · 1 mark · Details rearranging the concentration formula to find the required volume, including conversion and reason.

Worked solution

First, calculate the number of moles of the known reactant by multiplying its volume (converted to dm³) by its concentration. This tells you how many reacting particles you have.

Next, use the balanced chemical equation to determine the ratio of moles needed. This helps you work out how many moles of the second reactant are required to react completely.

Then, rearrange the concentration formula so that volume = moles / concentration. Substitute the moles from the previous step and the known concentration to find the required volume of solution. Remember to convert your answer into the correct unit (cm³ or dm³) as needed.