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Question 5

An analytical chemist investigates the rate of decomposition of a magnesium ribbon sample in hydrobromic acid, HBr(aq)\text{HBr(aq)}HBr(aq). The reaction is first-order with respect to HBr(aq)\text{HBr(aq)}HBr(aq).

  • The chemist first performs the reaction using 0.620 mol dm−3 HBr(aq)0.620\text{ mol dm}^{-3}\text{ HBr(aq)}0.620 mol dm−3 HBr(aq). The initial rate is 1.86×10−3 mol dm−3 s−11.86 \times 10^{-3}\text{ mol dm}^{-3}\text{ s}^{-1}1.86×10−3 mol dm−3 s−1.
  • The chemist dilutes a separate sample of this 0.620 mol dm−3 HBr(aq)0.620\text{ mol dm}^{-3}\text{ HBr(aq)}0.620 mol dm−3 HBr(aq) with deionised water. The pH of this diluted acid is 1.651.651.65.
  • The chemist repeats the reaction using the same volume of this diluted acid under identical conditions.

Determine the initial rate of the reaction using this diluted acid. Give your answer to 3 significant figures.

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How fast? Questions

  1. A Level
  2. /Chemistry
  3. /How fast?

29 exam-style questions on OCR A A Level Chemistry How fast?. Each one has a worked solution and a mark scheme showing where the marks go.

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