Question detail
If 10 grams of reactant A (Mr = 50) is used in a reaction with 20 grams of reactant B (Mr = 40), how many moles of A are present?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Use of amount of substance in relation to masses of pure substances
Question
- A. 0.2 moles
- B. 0.4 moles
- C. 0.5 moles
- D. 0.6 moles
Answer
0.2 moles
Explanation
Using the formula moles = mass / Mr, we find that 10 g of A corresponds to 0.2 moles.
Common mistake
Confusing Limiting Reactants
Students often confuse the limiting reactant with the reactant in excess, thinking that the limiting reactant is the one that is present in the smallest amount by mass rather than by moles.
To fix this, students should focus on calculating the number of moles of each reactant and identify which one will be completely consumed first in the reaction.
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