Question detail
In the reaction 2H2 + O2 → 2H2O, how many grams of H2 are needed to react with 32 g of O2?
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. 8 g
- B. 16 g
- C. 32 g
- D. 64 g
Answer
32 g
Explanation
The balanced equation shows that 2 moles of H2 react with 1 mole of O2. The molar mass of O2 is 32 g, which corresponds to 1 mole. Therefore, 2 moles of H2 (which is 2 * 2 g = 4 g) are needed for 1 mole of O2, so 32 g of O2 requires 64 g of H2.
Common mistake
Confusing Mass and Moles
Students often confuse the mass of a substance with the number of moles when calculating the masses of reactants from a balanced symbol equation.
To fix this, remember to use the formula that relates mass, moles, and relative formula mass: mass = moles x Mr. Ensure you calculate the number of moles first before converting to mass. Keep the correction anchored to Amounts of substances in equations (HT only); check formula, substitution, calculation, final answer, and unit where relevant.
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