Question detail
A solution of hydrochloric acid (HCl) has a concentration of 0.5 mol/dm³. How many moles of HCl are present in 250 cm³ of this solution?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Amount of substance
Question
- A. 0.125 mol
- B. 0.5 mol
- C. 0.75 mol
- D. 1 mol
Answer
0.125 mol
Explanation
The correct option is 0.125 mol. Use Concentration in mol/dm3: concentration = moles / volume. The worked result is 0.125 mol. 0.125 mol is the best answer because it directly supports the AQA A-Level Chemistry objective to use titration results to calculate unknown concentrations. This reasoning is anchored to Titration calculations in Amount of substance, and it separates titration from similar A-Level ideas rather than relying on a vague recall statement. Other options are weaker if they use the wrong evidence, calculation, mechanism, observation, unit, or conclusion for this subtopic.
Common mistake
Incorrect Use of Mean Titre
Students often calculate unknown concentrations using individual titre values instead of the mean titre.
To fix this, first calculate the mean titre by adding all titre values and dividing by the number of titrations. Then use the mean titre in the concentration calculation. For example, if the titre values are 25.0 cm³, 25.5 cm³, and 24.5 cm³, the mean titre is (25.0 + 25.5 + 24.5) / 3 = 25.0 cm³. Use this mean titre in the formula: concentration (mol/dm³) = moles of solute / volume of solution (dm³).
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