AQA A-LEVEL CHEMISTRY PAPER 3 VERSION 1

AQA A-LEVEL CHEMISTRY PAPER 3 VERSION 1 AQA A-LEVEL CHEMISTRY PAPER 3 VERSION 1 A-level CHEMISTRY Paper 3 Wednesday 20 June 2018 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 the 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. • 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 about 70 minutes on Section A and 50 minutes on Section B. *jun1 * IB/M/Jun18/E10 7405/3 Do not write outside the box Section A Answer all questions in this section. Iodide ions are oxidised to iodine by hydrogen peroxide in acidic conditions. H2O2(aq) + 2H+(aq) + 2I–(aq)  I2(aq) + 2H2O(l) The rate equation for this reaction can be written as rate = k [H2O2]a [I–]b [H+]c In an experiment to determine the order with respect to H+(aq), a reaction mixture is made containing H+(aq) with a concentration of 0.500 mol dm–3 A large excess of both H2O2 and I– is used in this reaction mixture so that the rate equation can be simplified to rate = k1 [H+]c . Explain why the use of a large excess of H2O2 and I– means that the rate of reaction at a fixed temperature depends only on the concentration of H+(aq). [2 marks] . Samples of the reaction mixture are removed at timed intervals and titrated with alkali to determine the concentration of H+(aq). State and explain what must be done to each sample before it is titrated with alkali. [2 marks] 0 1 . 3 A graph of the results is shown in Figure 1. Figure 1 Explain how the graph shows that the order with respect to H+(aq) is zero. [2 marks] . Use the graph in Figure 1 to calculate the value of k1 Give the units of k1 [3 marks] k1 Units Turn over ► . A second reaction mixture is made at the same temperature. The initial concentrations of H+(aq) and I–(aq) in this mixture are both 0.500 mol dm–3 There is a large excess of H2O2 In this reaction mixture, the rate depends only on the concentration of I–(aq). The results are shown in Table 1. Table 1 Time / s 0 100 200 400 600 800 1000 1200 [H+] / mol dm–3 0.50 0.44 0.39 0.31 0.24 0.19 0.15 0.12 Plot these results on the grid in Figure 2. The first three points have been plotted. [1 mark] Figure 2 [1 mark] . Calculate the rate of reaction when [H+] = 0.35 mol dm–3 Show your working using a suitable construction on the graph in Figure 2. [2 marks] Rate mol dm–3 s–1 Question 1 continues on the next page Turn over ► . A general equation for a reaction is shown. A(aq) + B(aq) + C(aq)  D(aq) + E(aq) In aqueous solution, A, B, C and D are all colourless but E is dark blue. A reagent (X) is available that reacts rapidly with E. This means that, if a small amount of X is included in the initial reaction mixture, it will react with any E produced until all of the X has been used up. Explain, giving brief experimental details, how you could use a series of experiments to determine the order of this reaction with respect to A. In each experiment you should obtain a measure of the initial rate of reaction. [6 marks] *07* Turn over ► The elements sodium to sulfur in Period 3 all react with oxygen to form oxides. 0 2 . 1 Give an equation and two observations made for the reaction that occurs when sodium is heated in oxygen. [2 marks] Equation Observation 1 Observation 2 0 2 . 2 Give an equation and one observation made for the reaction that occurs when phosphorus is heated in oxygen. [2 marks] Equation Observation . The melting points of the highest oxides of the elements sodium to sulfur are shown in Table 2. Table 2 Highest oxide of sodium magnesium aluminium silicon phosphorus sulfur Melting point / K 1548 3125 2345 1883 573 290 Explain the increase in melting point from sodium oxide to magnesium oxide. [2 marks] *0* . Explain why the melting point of the oxide of silicon is much higher than that of the highest oxide of phosphorus. [3 marks] . A sample of the highest oxide of phosphorus was prepared in a laboratory. Describe a method for determining the melting point of the sample. State how the result obtained could be used to evaluate its purity. [3 marks] Turn over ► 0 3 Cyclohexene (boiling point = 83 °C) can be prepared by the dehydration of cyclohexanol (boiling point = 161 °C) using concentrated phosphoric acid. A student prepared cyclohexene by placing 10 cm3 of cyclohexanol (density = 0.96 g cm–3) into a round-bottomed flask. 3 cm3 of concentrated phosphoric acid were then carefully added to the flask. The student added a few anti-bumping granules and set up the apparatus shown in Figure 3. Figure 3 • The student heated the mixture and collected the liquid that distilled at temperatures below 100 °C • The distillate was poured into a separating funnel and washed by shaking with sodium carbonate solution. • Periodically, the separating funnel was inverted and the tap opened. • The aqueous layer was discarded and the final organic product was dried using anhydrous calcium chloride. • After the product was dried, the drying agent was removed by filtration under reduced pressure. . The student collected 5.97 g of cyclohexene in the experiment. Calculate the percentage yield of cyclohexene. [3 marks] Percentage yield % . Describe a test-tube reaction, on the product, to show that the cyclohexanol had been dehydrated. State what you would observe. [2 marks] . Suggest why sodium carbonate solution was used to wash the distillate. [1 mark] . Explain why it is important to open the tap of the separating funnel periodically. [1 mark] Question 3 continues on the next page Turn over ► . Give a property of anhydrous calcium chloride, other than its ability to absorb water, that makes it suitable as a drying agent in this preparation. [1 mark] . Describe the apparatus used to remove the drying agent by filtration under reduced pressure. Your description of the apparatus can be either a labelled diagram or a description in words. [2 marks] . A sample of cyclohexene has been contaminated with cyclohexanol. The cyclohexene can be separated from the cyclohexanol by column chromatography. Silica gel is used as the stationary phase and hexane as the mobile phase. Explain why cyclohexene has a shorter retention time than cyclohexanol. [2 marks] . Explain how an infrared spectrum would confirm that the cyclohexene obtained from the chromatography column did not contain any cyclohexanol. [1 mark] Turn over for the next question Turn over ► A student carried out an experiment to find the temperature rise for a reaction between hydrochloric acid and sodium hydroxide solution. • The student used a measuring cylinder to place 50 cm3 of 0.400 mol dm–3 hydrochloric acid into a glass beaker. • The student recorded the temperature at one-minute intervals for three minutes. • At the fourth minute the student added 50 cm3 of 0.400 mol dm–3 sodium hydroxide solution and stirred to mix the solutions, but did not record the temperature. • The student recorded the temperature at one-minute intervals for a further eight minutes. The results are shown in Table 3. Table 3 Time / min 0 1 2 3 4 5 6 7 8 9 10 11 12 Temperature / °C 19.8 19.8 19.8 19.8 21.4 21.7 21.6 21.5 21.4 21.3 21.2 21.1 . Plot a graph of temperature against time on the grid opposite. Use your graph to find the temperature rise, ∆T, at the fourth minute. Show your working on the graph by drawing suitable lines of best fit. [5 marks] ∆T °C . The uncertainty in each of the temperature readings from the thermometer used in this experiment was ±0.1° C Calculate the percentage uncertainty in the value for the temperature rise. [1 mark] Percentage uncertainty . Suggest a change to the experiment that would minimise heat loss. [1 mark] Turn over ► . Suggest and explain another change to the experiment that would decrease the percentage uncertainty in the use of the same thermometer. [2 marks] . A second student completed an experiment to determine the enthalpy of neutralisation for the reaction between ethanedioic acid solution (HOOCCOOH) and potassium hydroxide solution. The student added 25 cm3 of 0.80 mol dm–3 ethanedioic acid solution to 75 cm3 of 0.60 mol dm–3 potassium hydroxide solution. The temperature increased by 3.2 °C Give an equation for the reaction between ethanedioic acid solution and potassium hydroxide solution. Calculate the enthalpy change (∆H) per mole of water formed in this reaction. Assume that the specific heat capacity of the reaction mixture is 4.2 J K–1 g–1 Assume that the density of the reaction mixture is 1.00 g cm–3 [5 marks] Equation ∆H kJ mol–1 . In a similar experiment to that in Question 04.5, the enthalpy of neutralisation for the reaction between sulfuric acid and potassium hydroxide solution was found to be –57.0 kJ mol–1 per mole of water formed. Suggest an explanation for the difference between this value and your answer to Question 04.5. (If you were unable to obtain an answer to Question 04.5 you should assume a value of –28.5 kJ mol–1. This is not the correct answer.) [2 marks] Turn over for Section B *17* Turn over ► Section B Answer all questions in this section. Only one answer per question is allowed. For each answer completely fill in the circle alongside the appropriate answer. CORRECT METHOD WRONG METHODS If you want to change your answer you must cross out your original answer as shown. If you wish to return to an answer previously crossed out, ring the answer you now wish to select as shown. You may do your working in the blank space around each question but this will not be marked. Do not use additional sheets for this working. 0 5 Which can be both an empirical and molecular formula of a stable compound? [1 mark] A CH2O B P4O10 C NH2 D CH3 *1* 0 6 Which diagram shows the correct bonding and correct bond polarity in a molecule of oxygen difluoride? [1 mark] A B C D Turn over for the next question Turn over ► In the early twentieth century the apparatus shown in the diagram was used to investigate atomic structure. When He2+ particles were fired at a thin sheet of gold, most of the particles were detected at point P. 0 7 What conclusion can be drawn from the detection of He2+ particles at point P? [1 mark] A Gold atoms contain electrons. B Gold atoms contain protons. C Gold atoms contain neutrons. D Gold atoms are mainly empty space. When He2+ particles were fired at a thin sheet of gold, about 1 in 8000 of the particles were detected at point Q. 0 8 What conclusion can be drawn from the detection of He2+ particles at point Q? [1 mark] A Gold atoms have a small, positive nucleus. B Gold atoms have electrons in orbitals. C Gold consists of ions in a sea of delocalised electrons. D Gold atoms have more protons than He2+ particles. 0 9 Which equation represents a termination step? [1 mark] A B C D 1 0 Which statement is correct about the molecule shown? [1 mark] A It reacts with HBr in an electrophilic substitution reaction. B It reacts with NaBH4 in a nucleophilic addition-elimination reaction. C It reacts with ethanolic KOH in an elimination reaction. D It reacts with KCN in a nucleophilic substitution reaction. 1 1 Which statement is correct about both 2-methylbutan-1-ol and 2-methylbutan-2-ol? [1 mark] A They can be formed by alkaline hydrolysis of esters. B They can be oxidised by reaction with acidified potassium dichromate(VI). C They can be formed by hydration of 2-methylbut-2-ene. D They have four peaks in their 13C NMR spectra. Turn over ► 1 2 Solutions of two compounds, W and X, react together in the presence of a soluble catalyst, Y, as shown in the equation 2W + X  Z When the concentrations of W, X and Y are all doubled, the rate of reaction increases by a factor of four. Which is a possible rate equation for this reaction? [1 mark] A rate = k [W]2 [X] B rate = k [W]2 [Y] C rate = k [X] [Y] D rate = k [X] [Z] 1 3 A series of experiments was carried out to find the order of reaction with respect to reactant X. In these experiments, only the concentration of X was changed. Which graph would show that the reaction is second-order with respect to X? [1 mark] A B C D 1 4 Which equation represents the process that occurs when the standard enthalpy of atomisation of iodine is measured? [1 mark] A 1 I (s)