A-level CHEMISTRY Paper 2 Organic and Physical Chemistry

A-level CHEMISTRY Paper 2 Organic and Physical Chemistry Tuesday 18 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 105. Answer all questions in the spaces provided. box Propanone reacts with bromine in alkaline conditions. CH3COCH3 + Br2 + OH– ⟶ CH3COCH2Br + Br – + H2O The rate equation for this reaction is Rate = k [CH3COCH3] [OH–] . Sketch a graph on the axes provided to show how, at constant temperature, the concentration of bromine changes during this reaction. [1 mark] . Table 1 shows the initial rate of this reaction for experiments using different mixtures containing propanone, bromine and hydroxide ions. Table 1 box Experiment [CH3COCH3] / mol dm–3 [Br2] / mol dm–3 [OH–] / mol dm–3 Initial rate / mol dm–3 s–1 1 1.50 × 10–2 2.50 × 10–2 2.50 × 10–2 2.75 × 10–11 2 1.50 × 10–2 2.50 × 10–2 8.25 × 10–11 3 3.75 × 10–3 5.00 × 10–2 1.00 × 10–1 Complete Table 1. Use the data from experiment 1 to calculate the rate constant k for this reaction. Give the units for the rate constant. [5 marks] k Units Question 1 continues on the next page Turn over ► . Figure 1 shows an incomplete mechanism for this reaction. Figure 1 Complete the mechanism in Figure 1 by adding four curly arrows and any relevant lone pair(s) of electrons. box [4 marks] . Use evidence from the rate equation to explain why Step 1 is the rate determining step. [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 an equilibrium. 2 P(aq) + Q(aq) ⇌ R(aq) + 3 S(aq) A 25.0 cm3 sample of a solution of P is added to a 20.0 cm3 sample of a solution of Q. The mixture is allowed to reach equilibrium. The amounts in the equilibrium mixture are P = 0.0145 mol Q = 0.0275 mol R = 0.0115 mol S = 0.0345 mol box 0 2 . 1 Calculate the amount, in moles, of P before the reaction with Q. Use your answer to calculate the concentration, in mol dm–3, of P in the initial 25.0 cm3 sample. [2 marks] Amount of P mol Concentration mol dm–3 box . Explain why the amount of S increases when water is added to the equilibrium mixture. [2 marks] Turn over for the next question *07* Turn over ► This question is about hydrocarbons. box 0 3 . 1 Eicosane (C20H42) can be cracked by heating to 700 K in the presence of a catalyst. The products are • an aromatic hydrocarbon C8H10 • an alkane C6H14 • another alkane. C20H42 ⟶ C8H10 + C6H14 + Complete the equation for this reaction. Give a suitable catalyst for this reaction. [2 marks] Catalyst . *0* Figure 2 shows the 13C NMR spectrum for the aromatic hydrocarbon C8H10 Figure 2 Which of these is the structure of C8H10? [1 mark] Tick () one box. A B C D . Cracking can also be done without a catalyst, using a temperature of 1200 K and a pressure of 7000 kPa State the type of product that is formed in high percentage in this type of cracking. [1 mark] Question 3 continues on the next page Turn over ► 0 3 . 4 A sample of butane has a volume of 20 cm3 at room temperature and pressure. The sample is burned completely in 1350 cm3 of air. The final mixture is cooled to room temperature and pressure. C4H10 + 6 1 O2 ⟶ 4 CO2 + 5 H2O 2 Calculate the total volume of gas in the final mixture. Assume that air contains 21% by volume of oxygen. [4 marks] Total volume of gas remaining cm3 . Natural gas is used in power stations to produce electricity. Natural gas contains sulfur impurities. Sulfur dioxide forms when these impurities are burned. State an environmental problem caused by sulfur dioxide. Give the formula of a compound that is used to help remove sulfur dioxide from the combustion products. [2 marks] Environmental problem Formula of compound Turn over for the next question DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED box Turn over ► This question is about the preparation of an ester. 0 4 . 1 Ester F can be prepared from propan-2-ol and ethanoic acid. Give an equation for this reaction. Name ester F. [2 marks] Equation Name This method is used to prepare a sample of ester F. Step 1 Mix 10 cm3 of propan-2-ol with 10 cm3 of ethanoic acid. Add 5 drops of concentrated sulfuric acid. Reflux this reaction mixture for 20 minutes. Step 2 Transfer the cooled reaction mixture to a separating funnel. Add 20 cm3 of aqueous sodium carbonate and shake the mixture. Step 3 Transfer the organic layer to a beaker and add 5 g of anhydrous magnesium sulfate. Decant off the organic liquid. Step 4 Collect the ester using simple distillation. box . Describe how Step 1 should be done. In your description you should • give details of suitable equipment used to add each reagent to the reflux apparatus • draw a labelled diagram of the apparatus used for refluxing the reaction mixture • explain any safety precautions needed other than eye protection. [6 marks] Question 4 continues on the next page Turn over ► 0 4 . 3 In Step 2 the reaction mixture from Step 1 is shaken with aqueous sodium carbonate. State the purpose of the sodium carbonate. Suggest a precaution that should be taken while this mixture is shaken in the separating funnel. Give a reason for your suggested precaution. [3 marks] Purpose of sodium carbonate Precaution Reason . Give the reason for the use of anhydrous magnesium sulfate in Step 3. [1 mark] . Suggest how the purity of the ester can be confirmed during the distillation in Step 4. [1 mark]