A-level CHEMISTRY Paper 3

A-level CHEMISTRY Paper 3 Friday 21 June 2024 Morning Time allowed: 2 hours Materials For this paper you must have: • the Periodic Table/Data Booklet, provided as an insert (enclosed) • a ruler with millimetre measurements • a scientific calculator, which you are expected to use where appropriate. Instructions • Use black ink or black ball-point pen. • Fill in the boxes at the top of this page. • Answer all questions. • You must answer the questions in the spaces provided. Do not write outside the box around each page or on blank pages. • If you need extra space for your answer(s), use the lined pages at the end of this book. Write the question number against your answer(s). • All working must be shown. • Do all rough work in this book. Cross through any work you do not want to be marked. Information • The marks for questions are shown in brackets. • The maximum mark for this paper is 90. Advice • You are advised to spend 70 minutes on Section A and 50 minutes on Section B. Section A Answer all questions in this section. box The structure of 2-hydroxybenzenecarboxylic acid is shown. . Give the equation for the reaction of 2-hydroxybenzenecarboxylic acid with methanol. In your equation, include the skeletal formula of the organic product. [2 marks] Aspirin is produced from 2-hydroxybenzenecarboxylic acid by reaction with ethanoic anhydride in the presence of concentrated phosphoric acid. Method 1. Add 2-hydroxybenzenecarboxylic acid to a conical flask. 2. Add excess ethanoic anhydride. 3. Add a few drops of concentrated phosphoric acid. 4. Heat the flask to 85 °C for 10 minutes. 5. Cool the flask and pour the contents into 150 cm3 of cold water. 6. Filter and wash the impure solid aspirin. 7. Recrystallise the aspirin using a 50:50 mixture of water and ethanol. 8. Check the purity of the aspirin. . Aspirin can also be produced by reacting 2-hydroxybenzenecarboxylic acid with ethanoyl chloride. State why ethanoic anhydride is preferred to ethanoyl chloride for this preparation. [1 mark] . Give the name of the mechanism for the reaction of 2-hydroxybenzenecarboxylic acid with ethanoic anhydride. [1 mark] box . Suggest the role of the concentrated phosphoric acid. [1 mark] . Suggest why reflux is not essential when the flask is heated to 85 °C for 10 minutes. [1 mark] . Complete and label the diagram to show how the impure solid is filtered. [2 marks] Question 1 continues on the next page Turn over ► 0 1 . 7 Suggest the identity of two impurities present in the filtered solid aspirin before it is washed in Step 6 of the method. [2 marks] Impurity 1 Impurity 2 . Describe the recrystallisation process used to purify the aspirin. Include the method and apparatus used. [6 marks] Turn over ► The rate of reaction between calcium carbonate and hydrochloric acid is investigated using a continuous monitoring method. Method • Place a conical flask on a balance and add approximately 20 g of large marble chips. • Add 50 cm3 of 0.4 mol dm–3 hydrochloric acid. • Place a loose cotton wool plug in the neck of the flask. • Zero the mass reading on the balance. • Start a timer. • Record the loss in mass (mt) every 30 seconds for 4 minutes. • Wait for the reaction to finish and record the total mass loss (mtotal). • Plot a graph of (mtotal – mt) against time. box Figure 1 shows a graph of the results obtained during the first 240 s Figure 1 0 2 . 1 Suggest why a loose cotton wool plug is placed in the neck of the flask, instead of leaving the flask open or inserting a bung. [2 marks] Instead of leaving the flask open Instead of inserting a bung . 20 g of large marble chips is a large excess of calcium carbonate. Suggest why using a large excess of calcium carbonate means that the rate is only affected by the changing concentration of the hydrochloric acid. box [1 mark] . The mass of carbon dioxide produced in time t is equal to mt. The total mass of CO2 produced during the reaction is equal to mtotal. Explain why (mtotal – mt) is proportional to the concentration of hydrochloric acid remaining in the flask at time t. [2 marks] Question 2 continues on the next page *07* Turn over ► . Table 1 shows the rate of reaction, calculated from the gradient of the curve, at five different times. (mtotal – mt) is proportional to the concentration of unreacted HCl at time t. Table 1 box Rate of reaction / g s–1 23.0 × 10–4 19.0 × 10–4 15.7 × 10–4 11.5 × 10–4 6.67 × 10–4 (mtotal – mt) / g 0.340 0.280 0.225 0.170 0.100 On the grid in Figure 2 plot the rate of reaction (y-axis) against (mtotal – mt) (x-axis).