2024 O Level Chem P1 Q1 — Rate of Reaction Solution
Question
Two experiments measure the volume of gas produced during the first 30s of a reaction. The method of gas collection is changed, but all other conditions are kept the same. The results are shown. Which statement explains why the volume of gas produced after 30s is different in the two experiments?
Correct answer: B
Video Solution
Explanation
Answer: B. The two experiments differ only in collection method — exp 1 collects over water, exp 2 in a gas syringe. The exp 1 reading (28 cm³) is lower because some of the gas dissolves in the water before reaching the measuring cylinder. The syringe in exp 2 isolates the gas from water entirely, giving the true volume (32 cm³).
The other options fail: A — gas collected in a syringe starts empty, so air can't contaminate; C — the rate experiment is timed identically, so completeness isn't the issue; D — a leak would lose gas, lowering exp 2's reading, but exp 2 is the higher of the two.
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