Question detail
What is the formula to calculate the number of moles from mass?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Mathematical requirements and assessment objectives
Question
- A. moles = mass / Mr
- B. moles = mass / volume
- C. moles = volume / mass
- D. moles = mass x Mr
Answer
moles = mass / Mr
Explanation
The correct option is moles = mass / Mr. moles = mass / Mr is the best answer because it directly supports the AQA A-Level Chemistry objective to apply knowledge and understanding in theoretical, practical, qualitative and quantitative contexts. This reasoning is anchored to Assessment objectives and paper structure in Mathematical requirements and assessment objectives, and it separates apply 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
Misidentifying the role of the catalyst in a reaction
Students often think a catalyst is consumed during the reaction and therefore must be added in stoichiometric amounts.
Explain that a catalyst is not consumed; it only provides an alternative reaction pathway and is present in the same amount before and after the reaction. It should be added in catalytic (small) amounts and can be recovered and reused.
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