Question detail
What is the percentage yield if 10 g of NaOH is produced from 20 g of Na reacting with excess water?
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. 50%
- B. 75%
- C. 100%
- D. 125%
Answer
50%
Explanation
The theoretical yield of NaOH from 20 g of Na is 20 g (since 1 mole of Na produces 1 mole of NaOH). The actual yield is 10 g, so the percentage yield is (10 g / 20 g) * 100 = 50%.
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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