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Question 4

A student investigates the rate of the acid-catalysed hydrolysis of ethyl ethanoate.

The student mixes 10.0 cm310.0\text{ cm}^310.0 cm3 of 0.020 mol dm−30.020\text{ mol dm}^{-3}0.020 mol dm−3 ethyl ethanoate with 10.0 cm310.0\text{ cm}^310.0 cm3 of 2.0 mol dm−32.0\text{ mol dm}^{-3}2.0 mol dm−3 hydrochloric acid (acting as the catalyst in large excess). Because the acid is in template excess, the reaction is effectively zero-order with respect to hydrogen ions.

The concentration of ethyl ethanoate is monitored over time, and the student plots a graph of concentration of ethyl ethanoate against time as shown below:

A graph of the concentration of ethyl ethanoate against time. The y-axis represents "concentration of ethyl ethanoate / 10^{-2} mol dm^{-3}" with major grid lines labeled from 0 to 1.2 in steps of 0.2. The x-axis represents "time / min" with major grid lines labeled from 0 to 12 in steps of 1. The curve starts at (0, 1.00) and smoothly declines through the following coordinate points: (1, 0.84), (2, 0.71), (3, 0.59), (4, 0.50), (5, 0.42), (6, 0.35), (7, 0.30), (8, 0.25), (9, 0.21), (10, 0.18), (11, 0.15), and (12, 0.13).

a.

Using collision theory, explain why the gradient of the curve decreases over time.

[2]
b.

Use the graph to determine:

  1. the order of reaction with respect to ethyl ethanoate,
  2. the rate of reaction at 5.0 minutes5.0\text{ minutes}5.0 minutes (include units),
  3. the rate constant, kkk (include units).
[8]

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