Page 12 30. The term accuracy is used to describe how close an experimental result is to the theoretical value. The term precision is used to describe how close a set of duplicate results are to each other. Four students determined the percentage by mass of chlorine in BaCl2. 2H2O. Which of the following sets of results is both accurate and precise? A 29·0%, 29·0%, 29·1% B 29·1%, 28·2%, 29·9% C 34·0%, 34·1%, 34·0% D 34·0%, 34·3%, 33·8% [END OF SECTION 1. NOW ATTEMPT THE QUESTIONS IN SECTION 2 OF YOUR QUESTION AND ANSWER BOOKLET] AH FOR OFFICIAL USE Fill in these boxes and read what is printed below. Number of seat Town © Mark Full name of centre Forename(s) Surname Scottish candidate number Date of birth Year Day Month National Qualications 2017 You may refer to the Chemistry Data Booklet for Higher and Advanced Higher. Total marks — 100 SECTION 1 — 30 marks Attempt ALL questions. Instructions for the completion of Section 1 are given on Page 02. SECTION 2 — 70 marks Attempt ALL questions. Write your answers clearly in the spaces provided in this booklet. Additional space for answers and rough work is provided at the end of this booklet. If you use this space you must clearly identify the question number you are attempting. Any rough work must be written in this booklet. You should score through your rough work when you have written your final copy. Use blue or black ink. Before leaving the examination room you must give this booklet to the Invigilator; if you do not, you may lose all the marks for this paper. X713/77/01 MONDAY, 8 MAY 9:00 AM – 11:30 AM A/PB Chemistry Section 1 — Answer Grid and Section 2 Page 02 SECTION 1 — 30 marks The questions for Section 1 are contained in the question paper X713/77/02. Read these and record your answers on the answer grid on Page 03 opposite. Use blue or black ink. Do NOT use gel pens or pencil. 1. The answer to each question is either A, B, C or D. Decide what your answer is, then fill in the appropriate bubble (see sample question below). 2. There is only one correct answer to each question. 3. Any rough working should be done on the additional space for answers and rough work at the end of this booklet. Sample Question To show that the ink in a ball-pen consists of a mixture of dyes, the method of separation would be: A fractional distillation B chromatography C fractional crystallisation D filtration. The correct answer is B — chromatography. The answer B bubble has been clearly filled in (see below). A B C D Changing an answer If you decide to change your answer, cancel your first answer by putting a cross through it (see below) and fill in the answer you want. The answer below has been changed to D. A B C D If you then decide to change back to an answer you have already scored out, put a tick (3) to the right of the answer you want, as shown below: A B C D or A B C D Page 03 A B C D 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 A B C D 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 SECTION 1 — Answer Grid [Turn over Page 04 [BLANK PAGE] DO NOT WRITE ON THIS PAGE Page 05 MARKS DO NOT WRITE IN THIS MARGIN SECTION 2 — 70 marks Attempt ALL questions 1. Many of the paints used by artists contain cadmium compounds. The presence of cadmium in a paint sample can be detected by atomic emission spectroscopy. (a) (i) Explain how a line is produced in an emission spectrum. (ii) Explain why there is a series of lines at discrete wavelengths in the emission spectrum of cadmium. (b) The cadmium emission spectrum has a line at 644 nm. Calculate the energy, in kJ mol−1, associated with this wavelength. 2 1 2 [Turn over Page 06 MARKS DO NOT WRITE IN THIS MARGIN 2. Phosphorus forms different compounds with chlorine. (a) When heated, phosphorus pentachloride dissociates to form phosphorus trichloride and chlorine. PCl5(g) Ý PCl3(g) + Cl2(g) ΔH = +124 kJ mol−1 In an experiment to determine the equilibrium constant, K, 0∙100 mol of PCl5 was placed in a sealed 1∙00 litre flask and heated to 250 °C. At equilibrium 0∙0420 mol of PCl3 had been formed. (i) Calculate the equilibrium constant, K, for the reaction at 250 °C. (ii) The temperature of the equilibrium mixture was increased to 400 °C. Explain the effect of this change in temperature on the value of the equilibrium constant, K. 3 2 Page 07 MARKS DO NOT WRITE IN THIS MARGIN 2. (continued) (b) In the solid state, phosphorus pentachloride is ionic and has the formula [PCl4]+[PCl6]−. (i) The three-dimensional structure for the [PCl4]+ ion is shown. Complete the table for the [PCl6]− ion. Phosphorus species Three-dimensional structure [PCl4]+ P Cl Cl Cl Cl + [PCl6]− (ii) Phosphorus oxychloride, POCl3, has a similar three-dimensional structure to the [PCl4]+ ion as shown. P Cl Cl Cl Cl + 109º P Cl Cl Cl O 103º Suggest a reason why the bond angle in the POCl3 molecule is less than the bond angle in the [PCl4]+ ion. 1 1 [Turn over Page 08 MARKS DO NOT WRITE IN THIS MARGIN 3. Zinc is often found in nature together with lead in sulfide ores. Different industrial processes can be used for the production of zinc metal. One of these is an electrolytic process and another is a thermal process. (a) In the electrolytic process, zinc sulfide is converted into zinc oxide by roasting in a furnace at 1300 K. 2ZnS(s) + 3O2(g) ↓ 2ZnO(s) + 2SO2(g) The data in the table refers to this reaction. Substance ΔHf° (kJ mol−1) S ° (J K−1 mol−1) ZnS(s) −206 58 O2(g) 0 205 ZnO(s) −350 44 SO2(g) −297 248 (i) For the conversion of zinc sulfide into zinc oxide, use the data in the table to calculate: (A) ΔH °, in kJ mol−1; (B) ΔS °, in J K−1 mol−1. (ii) Calculate the theoretical temperature, in K, above which the reaction is no longer feasible. 1 1 2 Page 09 MARKS DO NOT WRITE IN THIS MARGIN 3. (continued) (b) In the thermal process, a mixture of zinc oxide and lead oxide is reacted with carbon in a furnace at a temperature of 1200 K. Data for the metals and metal oxides are shown in the table below. Substance Density (g cm−3) Melting point (K) Boiling point (K) Zn 7·1 693 1181 Pb 11·3 600 2024 ZnO 5·6 2248 2633 PbO 9·5 1161 1808 By considering all the information, suggest how a sample of zinc metal and a sample of lead metal could each be removed from the furnace. [Turn over 2 Page 10 MARKS DO NOT WRITE IN THIS MARGIN 4. Transition metals, such as vanadium and copper, can have variable oxidation states and a wide range of uses. (a) Vanadium dioxide, VO2, can be used to coat glass. (i) State the oxidation number of vanadium in VO2. (ii) Using orbital box notation, write the electronic configuration, in terms of s, p and d orbitals, for the vanadium ion in VO2. (b) Vanadium(III) ions can react with iron(III) ions in solution. V3+(aq) + Fe3+(aq) ↓ V4+(aq) + Fe2+(aq) (i) The reaction is first order with respect to both V3+(aq) and Fe3+(aq). Write the rate equation for this reaction. 1 1 1 Page 11 MARKS DO NOT WRITE IN THIS MARGIN 4. (b) (continued) (ii) In the presence of a Cu2+(aq) catalyst, the reaction mechanism is: Cu2+(aq) + V3+(aq) slow ↓ Cu+(aq) + V4+(aq) Cu+(aq) + Fe3+(aq) fast ↓ Cu2+(aq) + Fe2+(aq) (A) State the order of the reaction with respect to Fe3+(aq) when a Cu2+(aq) catalyst is present. Explain your answer. (B) Explain why Cu2+(aq) can be described as a homogeneous catalyst in this reaction. (c) In the Middle Ages, Damascus steel was used for making sword blades. The steel from a sword blade of mass 1300 g was found to have a vanadium concentration of 71 ppm. Calculate the total mass of vanadium present in the sword blade. [Turn over 2 1 2 Page 12 MARKS DO NOT WRITE IN THIS MARGIN 5. A simple model of an atom is shown. Nucleus Subatomic particles electron proton neutron This simplistic model can be useful to help explain bonding but it is also misleading, as the structure of the atom and bonding are more complicated. Using your knowledge of chemistry, discuss the strengths and weaknesses of this simple model compared to the concepts of atomic structure and bonding at Advanced Higher level. 3 Page 13 DO NOT WRITE IN THIS MARGIN 5. (continued) [Turn over Page 14 MARKS DO NOT WRITE IN THIS MARGIN 6. Wilson’s disease is a rare genetic disorder which results in a build-up of copper ions in the body. Unmetabolised copper ions are toxic, leading to health complications. Copper ions can be removed by reaction with trientine. H2N N H H N NH2 trientine (a) Trientine is a tetradentate ligand that reacts with copper(II) ions in a 1:1 ratio to form a complex ion which can then be removed from the body. (i) Ligands form dative covalent bonds with metal ions. State what is meant by a dative covalent bond. (ii) Draw a structural formula for the complex ion. 1 1 Page 15 MARKS DO NOT WRITE IN THIS MARGIN 6. (continued) (b) Zinc ethanoate can also be used to treat Wilson’s disease. (i) Zinc ethanoate can be prepared from zinc hydroxide and ethanoic acid. Name this type of reaction. (ii) Zinc ethanoate is a salt of a weak acid. State what is meant by a weak acid. (iii) A student carried out an experiment to determine the value of y in hydrated zinc ethanoate, Zn(CH3COO)2.yH2O. A 5∙00 g sample was heated until all the water was removed and a constant mass of 4∙18 g was obtained. (A) Name the piece of apparatus that should be used to store the zinc ethanoate while cooling. (B) Calculate the value of y. (C) The student repeated the experiment with a second sample of hydrated zinc ethanoate. The student’s calculations were correct but the value of y was found to be different from the expected value. Suggest a reason for this difference. 1 1 1 2 1 [Turn over Page 16 MARKS DO NOT WRITE IN THIS MARGIN 7. Phenolphthalein is an indicator that can be prepared by the reaction of phenol with phthalic anhydride. (a) Phenolphthalein prepared by this method can have insoluble impurities present. It can be purified by recrystallisation from an aqueous ethanol solution. (i) Outline the steps that should be carried out to recrystallise phenolphthalein. (ii) Name a technique that could be used to determine if the recrystallised phenolphthalein is pure. (b) The equation for the reaction is given below. 2C6H6O + C8H4O3 C20H14O4 + H2O phenol phthalic phenolphthalein water anhydride (GFM = 94 g) (GFM = 148 g) (GFM = 318 g) (GFM = 18 g) 0∙96 g of phenol is reacted with 1∙05 g phthalic anhydride. In an experimental procedure, the percentage yield of phenolphthalein was 58%. Calculate the mass, in grams, of phenolphthalein produced. 2 1 3 Page 17 MARKS DO NOT WRITE IN THIS MARGIN 8. High levels of sugar in foods are associated with obesity. Sugars are also the basis of many medicines. (a) Glucose-fructose syrup is a type of sugar that is added to many foods. It is a mixture of glucose and fructose. The ring structures of glucose and fructose are shown below. O OH OH OH OH HO O HO OH OH HO HO glucose fructose (i) Write the molecular formula for fructose. (ii) Suggest, with reference to the structures, how 1H NMR spectroscopy could be used to distinguish between glucose and fructose. [Turn over 1 1 Page 18 MARKS DO NOT WRITE IN THIS MARGIN 8. (continued) (b) A more accurate representation of the structure of glucose, and its geometric isomer galactose, is shown below. O OH OH HO HO HO OH O OH OH HO OH glucose galactose With reference to the structures shown, explain why sugars such as glucose and galactose have geometric isomers. (c) The ring structure of glucose exists in equilibrium with its open-chain structure. The diagram below shows the open-chain structure of one optical isomer of glucose called D-glucose. D-glucose CH OH H OH OH H OH H OH H H O 2 C C C C C (i) State the number of chiral centres in D-glucose. (ii) Draw an open-chain structural formula for an optical isomer of D-glucose. 1 1 1 Page 19 MARKS DO NOT WRITE IN THIS MARGIN 8. (continued) (d) Relenza is a sugar-based medicine used to treat the flu virus. It acts by attaching to an enzyme active site on the virus. The structure of Relenza is shown. Relenza HO O OH O OH HN OH O N NH2 NH2 (i) Suggest how the functional groups circled on the Relenza molecule would bind with part of the enzyme active site. (ii) The structure of the natural active compound, sialic acid, is shown. sialic acid O HO OH O OH HN OH O OH OH Sialic acid binds to the same part of the enzyme active site as Relenza. Circle the functional groups on the sialic acid molecule which are most likely to bind with the enzyme active site. (An additional diagram, if required, can be found on Page 28) 1 1 [Turn over Page 20 MARKS DO NOT WRITE IN THIS MARGIN 9. A student devised the following reaction scheme starting with 1-methylcyclohexene. CH3 CH3 CH3 CH3 CH3 CH3 CH3 O OH NaOH(aq) compound Y 3 KCN in ethanol CN 2 COOH 1-methylcyclohexene compound X HBr 1 Br (a) In reaction 1 , 1-methylcyclohexene reacts with HBr to produce two compounds. (i) Draw a structural formula for compound X. (ii) Reaction 1 obeys Markovnikov’s rule. Explain, with reference to the carbocation intermediate, why compound X is the minor product in this reaction. 1 1 Page 21 MARKS DO NOT WRITE IN THIS MARGIN 9. (continued) (b) Suggest a reagent that could be used in reaction 2 . (c) Reaction 3 is likely to undergo an SN1 mechanism. Using curly arrow notation, draw the mechanism for this reaction. (d) Name compound Y. [Turn over 1 2 1 Page 22 MARKS DO NOT WRITE IN THIS MARGIN 10. An active ingredient in many stain removing products is the oxidising agent hydrogen peroxide, H2O2. (a) In an experiment to determine the concentration of hydrogen peroxide present in a stain remover a student carried out a titration with acidified permanganate solution. 2MnO4 − + 5H2O2 + 6H+ ↓ 2Mn2+ + 5O2 + 8H2O 5·0 cm3 of stain remover was pipetted into a 100 cm3 standard flask and made up to the mark with distilled water. 20·0 cm3 samples were titrated with 0·030 mol l−1 permanganate solution until a permanent pink colour remained. The results are shown in the table. 1st titration 2nd titration 3rd titration Initial burette reading (cm3) 0·3 19·2 0·2 Final burette reading (cm3) 19·2 37·7 18·8 Volume used (cm3) 18·9 18·5 18·6 (i) Calculate the number of moles of hydrogen peroxide in 20·0 cm3 of the diluted solution of stain remover. (ii) Calculate the concentration, in mol l−1, of hydrogen peroxide in the undiluted stain remover. 2 2 Page 23 MARKS DO NOT WRITE IN THIS MARGIN 10. (a) (continued) (iii) The concentration of hydrogen peroxide determined by the student was less than the concentration stated on the label for the stain remover. One possible source of error could be an inaccurate concentration of the permanganate solution. Describe how the student would confirm the concentration of the permanganate solution. [Turn over 1 Page 24 MARKS DO NOT WRITE IN THIS MARGIN 10. (continued) (b) Some of the molecules thought to be responsible for the colour of stains are shown. OH HO OH O OH O OH HO OH blackcurrant stain red wine stain tomato stain Using your knowledge of chemistry, suggest how the chemicals in a stain remover might work on these stains. 3 Page 25 MARKS DO NOT WRITE IN THIS MARGIN 10. (b) (continued) [Turn over Page 26 MARKS DO NOT WRITE IN THIS MARGIN 11. Nutmeg is a seed that is commonly used as a spice in cooking. The flavour of nutmeg is due to a number of different compounds. (a) The oil in nutmeg, trimyristin, can be easily extracted and purified. In an experiment to extract trimyristin, a student refluxed nutmeg powder in a suitable solvent. Removal of the solvent produced an impure sample of solid trimyristin. (i) Suggest why an ether could be a suitable solvent to extract trimyristin oil from nutmeg. (ii) Suggest why the mixture was heated under reflux. (b) Myristicin is another compound that can be isolated from nutmeg. 1H NMR analysis showed there to be seven proton environments and these are numbered on the skeletal formula shown. O O O 4 3 1 2 5 6 7 myristicin (i) Suggest a possible chemical shift for the peak arising due to proton environment 1. (ii) Identify a proton environment which would produce a doublet in the 1H NMR spectrum. 1 1 1 1 Page 27 MARKS DO NOT WRITE IN THIS MARGIN 11. (continued) (c) Myristicin can be converted into compound X in two steps. O O O O O O NH2 compound X myristicin Suggest the type of reaction occurring at each step. Step 1: Step 2: [END OF QUESTION PAPER] 2 Page 28 MARKS DO NOT WRITE IN THIS MARGIN ADDITIONAL DIAGRAM FOR USE IN QUESTION 8 (d) (ii) sialic acid O HO OH O OH HN OH O OH OH Page 29 MARKS DO NOT WRITE IN THIS MARGIN ADDITIONAL SPACE FOR ANSWERS AND ROUGH WORK Page 30 MARKS DO NOT WRITE IN THIS MARGIN ADDITIONAL SPACE FOR ANSWERS AND ROUGH WORK Page 31 [BLANK PAGE] DO NOT WRITE ON THIS PAGE Page 32 [BLANK PAGE] DO NOT WRITE ON THIS PAGE