A-Level AQA Chemistry Rate Equations: This question is about rates of

Question

This question is about rates of reaction.
Iodine and propanone react together in an acid-catalysed reaction

$$ CH_3C(=O)CH_3(aq) + I^-(aq) \rightarrow CH_3C(=O)I(aq) + H^+(aq) $$

A student completed a series of experiments to determine the order of reaction with respect to iodine.

**Method**

1. Transfer 25 cm³ of 1.0 mol dm⁻³ propanone solution into a conical flask.
2. Add 10 cm³ of 1.0 mol dm⁻³ HCl(aq).
3. Add 25 cm³ of 5.0 × 10⁻³ mol dm⁻³ I₂(aq) and start a timer.
4. After intervals of 1 minute, remove 1.0 cm³ sample of the mixture and add each sample to a separate beaker containing an excess of NaHCO₃(aq).
5. Titrate the contents of each beaker with a standard solution of sodium thiosulfate until the endpoint is reached.

The volume of sodium thiosulfate solution used in each titration is proportional to the concentration of iodine in each beaker.

**Table 5** shows the results of the experiment.

| Time / minutes | Volume of sodium thiosulfate solution / cm³ |
|----------------|------------------------------------------|
| 1              | 41                                       |
| 2              | 35                                       |
| 3              | 24                                       |
| 4              | 22                                       |
| 5              | 16                                       |
| 6              | 10                                       |

1.0.3 Use the results in Table 5 to draw a graph of volume of sodium thiosulfate solution against time.

Draw a line of best fit.

1.0.4 Explain how the graph shows that the reaction is zero-order with respect to iodine in the reaction between propanone and iodine.

1.0.5 The Arrhenius equation can be written as

$$ 	ext{ln } k = \frac{E_a}{RT} + \text{ln } A $$

Figure 8 shows a graph of $ 	ext{ln } k $ against $ \frac{1}{T} $ for the reaction

$$ 2H_{2}(g) \rightarrow H_{g}(g) + I_{g}(g) $$

Use Figure 8 to calculate a value for the activation energy (Eₐ), in kJ mol⁻¹, for this reaction.

The gas constant R = 8.31 J K⁻¹ mol⁻¹.

This question is about rates of reaction - AQA - A-Level Chemistry - Question 10 - 2021 - Paper 2

Worked Solution & Example Answer:This question is about rates of reaction - AQA - A-Level Chemistry - Question 10 - 2021 - Paper 2

Suggest why the 1.0 cm³ portions of the reaction mixture are added to an excess of NaHCO₃ solution.

Suggest why the order of this reaction with respect to propanone can be ignored in this experiment.

Draw a line of best fit.

Explain how the graph shows that the reaction is zero-order with respect to iodine in the reaction between propanone and iodine.

Use Figure 8 to calculate a value for the activation energy (Eₐ), in kJ mol⁻¹, for this reaction.

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