Page 11 30. 0·020 moles of the salt Pt(NH3)xCl2 required 20·0 cm3 of 4·0 mol l−1 nitric acid to react completely with the NH3 ligands. The value of x is A 2 B 4 C 6 D 8. [END OF SECTION 1. NOW ATTEMPT THE QUESTIONS IN SECTION 2 OF YOUR QUESTION AND ANSWER BOOKLET] Page 12 [BLANK PAGE] DO NOT WRITE ON THIS PAGE 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 2016 Reference may be made to the Chemistry Higher and Advanced Higher Data Booklet. 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 WEDNESDAY, 18 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 [Turn over for next question do not write on this page Page 06 MARKS DO NOT WRITE IN THIS MARGIN SECTION 2 — 70 marks Attempt ALL questions 1. Ethene can be hydrated to produce ethanol. C2H4(g) + H2O(ℓ) → C2H5OH(ℓ) Compound Standard free energy of formation, ΔG° (kJ mol−1) Standard enthalpy of formation, ΔH°f (kJ mol−1) Ethene 68 52 Water −237 −286 Ethanol −175 −278 (a) For the hydration of ethene, use the data in the table to calculate: (i) the standard enthalpy change, ΔH°, in kJ mol−1; (ii) the standard entropy change, ΔS°, in J K−1 mol−1. (b) Calculate the temperature, in K, at which this reaction just becomes feasible. 1 3 2 Page 07 MARKS DO NOT WRITE IN THIS MARGIN 2. In the periodic table, period 2 is comprised of the elements lithium to neon. The following table shows two of the quantum numbers for all ten electrons in a neon atom. Electron Principal quantum number, n Angular momentum quantum number, l 1 1 0 2 1 0 3 2 0 4 2 0 5 2 1 6 2 1 7 2 1 8 2 1 9 2 1 10 2 1 (a) Write the electronic configuration for neon in terms of s and p orbitals. (b) The angular momentum quantum number, l, is related to the shape of an orbital. Draw the shape of an orbital when l has a value of 1. (c) The magnetic quantum number, m, is related to the orientation of an orbital in space. State the values of m for the orbital which contains the tenth electron. 1 1 1 [Turn over Page 08 [BLANK PAGE] do not write on this page Page 09 MARKS DO NOT WRITE IN THIS MARGIN 3. Iron can form a variety of complexes with different ligands. Each complex has different properties. (a) Some iron complex ions are paramagnetic. Paramagnetic substances are substances that are weakly attracted by a magnetic field. Paramagnetism is caused by the presence of unpaired electrons. In both [Fe(H2O)6]2+ and [Fe(CN)6]4−, the Fe2+ ion has six d-electrons, but only [Fe(H2O)6]2+ is paramagnetic. (i) Complete the d-orbital box diagram for the complex ion [Fe(CN)6]4−. Energy ∆ (An additional diagram, if required, can be found on Page 28) (ii) The relative ability of a ligand to split the d-orbitals when forming a complex ion is given by the spectrochemical series. The spectrochemical series for some ligands is shown below. CN− > NH3 > H2O The [Fe(H2O)6]2+ ion has unpaired electrons and is therefore paramagnetic. Explain how unpaired electrons can arise in this complex ion. (iii) Explain why all of the complex ions formed by the Fe3+ ion are paramagnetic. 1 2 1 [Turn over Page 10 MArKS DO NOT WRITE IN THIS MARGIN 3. (continued) (b) Human blood is red due to the presence of haemoglobin bonded to oxygen. Other animals have different coloured blood due to the presence of different complex ions bonded to oxygen. Human Haemoglobin Oxyhaemocyanin RED Animal Complex ion Colour of blood N N N N H3C CH2 CH3 CH2 H3C O OH CH3 OH O Fe2+ Leech GREEN Spider BLUE Chlorocruorin N N N N O O OH OH O Fe2+ H3C CH3 CH2 H3C CH3 O O Cu Cu N N N NH N N N HN HN NH NH HN CH3 CH3 CH3 H3C H3C H3C 2+ 2+ (i) State the co-ordination number of the Fe2+ ion in haemoglobin. 1 Page 11 MARKS DO NOT WRITE IN THIS MARGIN 3. (b) (continued) (ii) Spiders’ blood contains the oxyhaemocyanin complex ion. Oxyhaemocyanin contains copper ions. Suggest an analytical technique that could be used to determine the presence of copper ions in spiders’ blood. (iii) Using your knowledge of chemistry, comment on why these animals have different coloured blood. [Turn over 1 3 Page 12 MARKS DO NOT WRITE IN THIS MARGIN 4. As part of an Advanced Higher Chemistry project, a student determined the chloride ion concentration of seawater by two different methods. Volumetric method A sample of seawater was titrated with standard silver nitrate solution. Gravimetric method A sample of seawater was reacted with standard silver nitrate solution to form a precipitate. The precipitate was collected by filtration and weighed. (a) For the volumetric method, a 0∙1 mol l−1 standard solution of silver nitrate was prepared by following the instructions below. 1. Dry 5 g of silver nitrate for 2 hours at 100 °C and allow to cool. 2. Weigh accurately approximately 4∙25 g of solid silver nitrate. 3. Use this sample to prepare 250 cm3 of standard silver nitrate solution. (i) State what is meant by “weigh accurately approximately” 4∙25 g of solid silver nitrate. (ii) Outline how the student would have prepared the standard silver nitrate solution. (iii) Samples of the diluted seawater were titrated and the average titre was found to be 3∙9 cm3. Suggest an improvement the student could make to reduce the uncertainty in the titre value. 1 2 1 Page 13 MARKS DO NOT WRITE IN THIS MARGIN 4. (continued) (b) For the gravimetric method, standard silver nitrate solution was added to a seawater sample to form a precipitate of silver chloride. (i) Describe how the filtration should have been carried out to ensure a fast means of separating the precipitate from the reaction mixture. (ii) After the precipitate was filtered, the filtrate was tested with a few drops of silver nitrate solution. Suggest why the student tested the filtrate in this way. (c) The student also planned to carry out an analysis of chloride ion concentration in fresh river water. Explain why the volumetric method, rather than the gravimetric method, would be more appropriate for the analysis of chloride ion concentration in fresh river water. [Turn over 1 1 1 Page 14 MArKS DO NOT WRITE IN THIS MARGIN 5. Mandelic acid, 2-hydroxy-2-phenylethanoic acid, is a component of skin care products. mandelic acid OH OH O (a) Mandelic acid is a weak acid. C6H5CH(OH)COOH(aq) + H2O(ℓ) Ý C6H5CH(OH)COO−(aq) + H3O+(aq) Write the expression for the dissociation constant, Ka, for mandelic acid. (b) A 100 cm3 sample of skin care product contained 10∙0 g of mandelic acid. The Ka of mandelic acid is 1∙78 × 10−4. (i) Calculate the concentration of the mandelic acid, in mol l−1, present in the skin care product. (ii) Using your answer to (b)(i), calculate the pH of a solution of mandelic acid of this concentration. 1 2 3 Page 15 [Turn over for next question do not write on this page Page 16 MARKS DO NOT WRITE IN THIS MARGIN 6. Chlorine is a versatile element which forms a wide range of compounds. (a) One example of a compound containing chlorine is vanadium(IV) chloride. It reacts vigorously with water forming a blue solution. The blue solution absorbs light of wavelength 610 nm. Calculate the energy, in kJ mol−1, associated with this wavelength. (b) Chlorine dioxide, ClO2, is used in water sterilisation. An experiment was carried out to determine the kinetics for the reaction between chlorine dioxide and hydroxide ions. 2ClO2(aq) + 2OH−(aq) → ClO2 −(aq) + ClO3 −(aq) + H2O(ℓ) Under certain conditions the following results were obtained. [ClO2] (mol l−1) [OH−] (mol l−1) Initial rate (mol l−1s−1) 6·00 × 10−2 3·00 × 10−2 2·48 × 10−2 1·20 × 10−1 3·00 × 10−2 9·92 × 10−2 1·20 × 10−1 9·00 × 10−2 2·98 × 10−1 (i) Determine the order of reaction with respect to: (A) ClO2 (B) OH− 2 1 1 Page 17 MARKS DO NOT WRITE IN THIS MARGIN 6. (b) (continued) (ii) Write the overall rate equation for the reaction. (iii) Calculate the value for the rate constant, k, including the appropriate units. 1 2 [Turn over Page 18 MArKS DO NOT WRITE IN THIS MARGIN 7. Aldehydes and ketones can exist in two forms, a keto form and an enol form. For example, the aldehyde ethanal exists in equilibrium with its enol form, ethenol. K = 3·0 × 10−7 ethanal (keto form) ethenol (enol form) H3C C O H H2C C H OH Ý These two different molecules are known as tautomers. (a) State which of the tautomers is the more abundant in this equilibrium. (b) 3-Methylpentan-2-one is optically active and exists in equilibrium with its enol tautomer. (i) Circle the chiral centre on 3-methylpentan-2-one. H3C CH3 H C C CH2 O H3C (ii) Suggest why the optical activity of 3-methylpentan-2-one decreases over time. 1 1 1 Page 19 MArKS DO NOT WRITE IN THIS MARGIN 7. (b) (continued) (iii) Draw the skeletal formula for 3-methylpentan-2-one. (c) A possible mechanism for acid-catalysed enolisation is shown below, where R, R' and R" are alkyl groups. C C R H H+ O .. .. .. R' R'' C C R H H O+ H+ .. R' R'' C C R H O .. R' R'' Ý Ý Using structural formulae and curly arrow notation, show a possible mechanism for the acid-catalysed enolisation of 3-methylpentan-2-one. 1 3 [Turn over Page 20 MARKS DO NOT WRITE IN THIS MARGIN 8. Aspirin can be used as a starting material for the synthesis of the drug, salbutamol, which is used in the treatment of asthma. Salbutamol acts as an agonist by stimulating receptors in the lungs. A possible synthetic route is shown. HO2C H3COCO HO2C HO O H3CO2C HO O H3CO2C HO O Br H3CO2C HO O N C H CH3 CH3 H3C HO OH N C H CH3 CH3 H3C HO AlCl3 CH3OH/H+ Br2 Step 1 Step 2 Step 3 Step 4 Step 5 (a) State what is meant by the term agonist. (b) Step ➀ is known as a Fries rearrangement. Suggest the role of AlCl3 in this rearrangement. 1 1 Page 21 MARKS DO NOT WRITE IN THIS MARGIN 8. (continued) (c) Suggest a reaction condition required for Step ➂. (d) Identify the type of reaction taking place in Step ➃. (e) Step ➄ involves several reactions. Suggest a suitable reagent that could be used to convert the ketone carbonyl group to the hydroxyl group. [Turn over 1 1 1 Page 22 MARKS DO NOT WRITE IN THIS MARGIN 8. (continued) (f) The purity of salbutamol can be determined using a variety of analytical techniques. Using your knowledge of chemistry, discuss how analytical techniques could be used to determine the purity of salbutamol. 3 Page 23 MARKS DO NOT WRITE IN THIS MARGIN 9. Parabens are used as preservatives in cosmetics, pharmaceutical products and foods. Parabens are esters of 4-hydroxybenzoic acid. One common paraben used as a food preservative is ethylparaben. O O OH ethylparaben (a) Ethylparaben is an aromatic compound containing both sigma and pi bonds. (i) Write the molecular formula for ethylparaben. (ii) State the type of hybridisation which is adopted by the carbon atoms in the aromatic ring. (iii) Describe how pi bonds form. [Turn over 1 1 1 Page 24 MARKS DO NOT WRITE IN THIS MARGIN 9. (continued) (b) Another preservative is sodium 4-hydroxybenzoate. It can be prepared by refluxing ethylparaben with sodium hydroxide solution. O O OH O O−Na+ OH CH3CH2OH Na + + +OH− (i) Complete the diagram below to show how the reaction mixture is heated under reflux. Heating mantle (An additional diagram, if required, can be found on Page 28) (ii) At the start of the reaction, two layers were observed in the reaction mixture. Explain why only one layer was observed when the reaction was complete. 1 1 Page 25 MARKS DO NOT WRITE IN THIS MARGIN 9. (b) (continued) (iii) Explain fully why a solution of the salt sodium 4-hydroxybenzoate has a pH greater than 7. (iv) After refluxing, dilute hydrochloric acid was added to the reaction mixture and a white precipitate of 4-hydroxybenzoic acid was produced. The crude 4-hydroxybenzoic acid was recrystallised. 4-hydroxybenzoic acid is soluble in different solvents but only some of these solvents are suitable for recrystallisation. State two factors that should be considered when selecting an appropriate solvent for this recrystallisation. (v) In this experiment, the percentage yield of 4-hydroxybenzoic acid was 77·5%. Calculate the mass of ethylparaben (GFM = 166 g) required to produce 2·48 g of 4-hydroxybenzoic acid (GFM = 138 g). [Turn over 2 2 2 Page 26 MArKS DO NOT WRITE IN THIS MARGIN 10. Phenylbutazone is an anti-inflammatory drug used for the short-term treatment of pain and fever in animals. (a) Phenylbutazone can be synthesised, in a multi-step process, starting from compound A. Elemental microanalysis showed that compound A has a composition, by mass, of 50∙0% C; 5∙60% H; 44∙4% O Calculate the empirical formula of compound A. (b) An infra-red spectrum for compound A is shown below. 3500 50 100 3000 2500 2000 Wave number (cm−1) Transmittance (%) 1500 1000 Identify the functional group responsible for the peak at 1710 cm−1. 2 1 Page 27 MArKS DO NOT WRITE IN THIS MARGIN 10. (continued) (c) The mass spectrum for compound A is shown below. m/z % 100 80 60 40 20 0 10 70 90 50 30 25 43 45 55 27 72 (i) Write the molecular formula for compound A. (ii) Suggest a possible ion fragment that may be responsible for the peak at m/z 27. (d) Considering all the evidence, draw a structural formula for compound A. [END OF QUESTION PAPEr] 1 1 1 Page 28 MARKS DO NOT WRITE IN THIS MARGIN ADDITIONAL DIAGRAM FOR USE IN QUESTION 3 (a) (i) Energy ∆ ADDITIONAL DIAGRAM FOR USE IN QUESTION 9 (b) (i) Heating mantle 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 ACKNOWLEDGEMENT Section 2 Question 3(b) – Anna Rassadnikova/shutterstock.com RATOCA/shutterstock.com vladis.studio/shutterstock.com