AQA A-LEVEL CHEMISTRY PAPER 2 QUESTION PAPER JUNE 2020

AQA A-LEVEL CHEMISTRY PAPER 2 QUESTION PAPER JUNE 2020 A-level CHEMISTRY Paper 2 Organic and Physical Chemistry Monday 8 June 2020 Afternoon 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 105. Answer all questions in the spaces provided. box 0 1 This question is about rates of reaction. Phosphinate ions (H2PO –) react with hydroxide ions to produce hydrogen gas as 2 shown. – − 2– H2PO2 + OH →HPO3 + H2 A student completed an experiment to determine the initial rate of this reaction. The student used a solution containing phosphinate ions and measured the volume of hydrogen gas collected every 20 seconds at a constant temperature. Figure 1 shows a graph of the student’s results. Figure 1 0 1 . 1 Use the graph in Figure 1 to determine the initial rate of reaction for this experiment. State its units. Show your working on the graph. [3 marks] Rate Units . Another student reacted different initial concentrations of phosphinate ions with an excess of hydroxide ions. The student measured the time (t) taken to collect 15 cm3 of hydrogen gas. Each experiment was carried out at the same temperature. Table 1 shows the results. Table 1 – –3 Initial [H2PO2 ] / mol dm t / s 0.25 64 0.35 32 0.50 16 1.00 4 State the relationship between the initial concentration of phosphinate and time (t). box Deduce the order of the reaction with respect to phosphinate. [2 marks] Relationship Order Question 1 continues on the next page Turn over ► . Complete the diagram in Figure 2 to show how the hydrogen gas could be collected and measured in the experiments in Questions 01.1 and 01.2. box [1 mark] Figure 2 The rate equation for a different reaction is rate = k [L] [M]2 . Deduce the overall effect on the rate of reaction when the concentrations of both L and M are halved. [1 mark] 0 1 . 5 The rate of reaction is 0.0250 mol dm–3 s–1 when the concentration of L is 0.0155 mol dm–3 Calculate the concentration of M if the rate constant is 21.3 mol–2 dm6 s–1 [3 marks] Concentration of M mol dm–3 . Define the term overall order of reaction. [1 mark] Turn over for the next question Turn over ► 0 2 Prilocaine is used as an anaesthetic in dentistry. Figure 3 shows the structure of prilocaine. Figure 3 . Draw a circle around any chiral centre(s) in Figure 3. [1 mark] . Identify the functional group(s) in the prilocaine molecule. [1 mark] Tick () the box(es) corresponding to the functional group(s). Amide Amine Ester Ketone . Prilocaine is completely hydrolysed in the human body to give a mixture of products. Draw the structures of the two organic products formed in the complete hydrolysis of prilocaine in acidic conditions. [3 marks] . Figure 4 shows optical isomers F and G. Figure 4 Isomer F is the active compound in the medicine ibuprofen. In the manufacture of ibuprofen both isomers F and G are formed. An enzyme is then used to bind to isomer G and catalyse its hydrolysis. After the products of hydrolysis of G are removed, a pure sample of isomer F is collected. Explain how a structural feature of this enzyme enables it to catalyse the hydrolysis of isomer G but not the hydrolysis of isomer F. box [2 marks] Turn over for the next question *07* Turn over ► 0 3 *0* This question is about the structural isomers shown. box box . State the type of structural isomerism shown by isomers P, Q, R and S. [1 mark] . Describe fully how infrared spectra can be used to distinguish between isomers R, S and T. Use data from Table A in the Data Booklet in your answer. [4 marks] . State why mass spectrometry using electrospray ionisation is not a suitable method to distinguish between the isomers. [1 mark] Turn over ► Aspirin can be produced by reacting salicylic acid with ethanoic anhydride. An incomplete method to determine the yield of aspirin is shown. 1. Add about 6 g of salicylic acid to a weighing boat. 2. Place the weighing boat on a 2 decimal place balance and record the mass. 3. Tip the salicylic acid into a 100 cm3 conical flask. 4. 5. Add 10 cm3 of ethanoic anhydride to the conical flask and swirl. 6. Add 5 drops of concentrated phosphoric acid. 7. Warm the flask for 20 minutes. 8. Add ice-cold water to the reaction mixture and place the flask in an ice bath. 9. Filter off the crude aspirin from the mixture and leave it to dry. 10. Weigh the crude aspirin and calculate the yield. box 0 4 . 1 Describe the instruction that is missing from step 4 of the method. Justify why this step is necessary. [2 marks] Instruction Justification . Suggest a suitable piece of apparatus to measure out the ethanoic anhydride in step 5. [1 mark] . Identify a hazard of using concentrated phosphoric acid in step 6. [1 mark] . Complete the equation for the reaction of salicylic acid with ethanoic anhydride to produce aspirin. box [1 mark] . A 6.01 g sample of salicylic acid (Mr = 138.0) is reacted with 10.5 cm3 of ethanoic anhydride (Mr = 102.0). In the reaction the yield of aspirin is 84.1% The density of ethanoic anhydride is 1.08 g cm–3 Show by calculation which reagent is in excess. Calculate the mass, in g, of aspirin (Mr = 180.0) produced. [5 marks] Reagent in excess Mass of aspirin g Turn over ► box 0 4 . 7 The crude aspirin can be purified by recrystallisation using hot ethanol (boiling point = 78 °C) as the solvent. Describe two important precautions when heating the mixture of ethanol and crude aspirin. [2 marks] Precaution 1 Precaution 2 . The pure aspirin is filtered under reduced pressure. A small amount of cold ethanol is then poured through the Buchner funnel. Explain the purpose of adding a small amount of cold ethanol. [1 mark] . A sample of the crude aspirin is kept to compare with the purified aspirin. Describe one difference in appearance you would expect to see between these two solid samples. [1 mark] Turn over for the next question DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED box Turn over ► This question is about 2-bromopropane. box 0 5 . 1 Define the term electronegativity. Explain the polarity of the C–Br bond in 2-bromopropane. [3 marks] Electronegativity Explanation . Outline the mechanism for the reaction of 2-bromopropane with an excess of ammonia. [4 marks] . Draw the skeletal formula of the main organic species formed in the reaction between a large excess of 2-bromopropane and ammonia. box Give a use for the organic product. [2 marks] Skeletal formula Use Turn over for the next question Turn over ► Polystyrene can be made from benzene in the series of steps shown. box 0 6 . 1 State the type of reaction in step 1. Identify the reagent(s) and conditions needed for step 1. [3 marks] Type of reaction Reagent(s) Conditions 0 6 . 2 State the name of the mechanism for the reaction in step 2. Identify the inorganic reagent needed for step 2. Name the organic product of step 2. [3 marks] Name of mechanism Inorganic reagent Name of organic product . The organic product of step 2 is reacted with concentrated sulfuric acid in step 3. box Outline the mechanism for step 3. [3 marks] . Draw the repeating unit of polystyrene. [1 mark] Turn over for the next question *17* Turn over ► This question is about NMR spectroscopy. box . A compound is usually mixed with Si(CH3)4 and either CCl4 or CDCl3 before recording the compound’s 1H NMR spectrum. State why Si(CH3)4, CCl4 and CDCl3 are used in 1H NMR spectroscopy. Explain how their properties make them suitable for use in 1H NMR spectroscopy. [6 marks] *1* Question 7 continues on the next page Turn over ► 0 7 . 2 Deduce the splitting pattern for each of the peaks given by the H atoms labelled x, y and z in the 1H NMR spectrum of the compound shown. [3 marks] x y z . Suggest why it is difficult to use Table B in the Data Booklet to predict the chemical shift (δ value) for the peak given by the H atom labelled y. [1 mark] 0 7 . 4 Two isomers of CH3CHClCOCH(CH3)2 each have two singlet peaks only in their 1H NMR spectra. In both spectra the integration ratio for the two peaks is 2:9 Deduce the structures of these two isomers. [2 marks] Isomer 1 Isomer 2 This question is about citric acid, a hydrated tricarboxylic acid. Its formula can be represented as H3Y.