page 12 29. When substance X is distributed between equal volumes of two immiscible solvents, water and dichloromethane, an equilibrium will be established. X(H2O)  ∏  X(CH2Cl2)      K = 4 In the diagrams below, the number of dots represents the relative distribution of X in the two solvents. Water is less dense than dichloromethane. Which of the following shows the correct distribution of X between the two solvents at equilibrium? H2O H2O CH2Cl2 CH2Cl2 H2O H2O CH2Cl2 CH2Cl2 A B C D 30. A complexometric titration can be used to determine the concentration of A calcium ions in milk B chloride ions in sea water C ethanoic acid in vinegar D ethanol in wine. [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 2019 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 FRIDAY, 10 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. Chlorine forms many compounds with other elements. (a) The electronic configuration for a chlorine atom in its ground state is shown. 2p 1s 2s 3s 3p Circle one electron in the above diagram that can be described by the following set of quantum numbers. n = 2, l = 1, m = −1, s = + (An additional diagram, if required, can be found on page 28.) (b) A compound of chlorine, boron trichloride, reacts with hydrogen to produce boron. BCl3(g)  + H2(g)  ↓  B(s)  +  3HCl(g)      ∆H ° = 127 kJ mol−1 The standard entropy change, ∆S °, is 79·4 J K−1 mol−1. Calculate ∆G °, in kJ mol−1, for this reaction at 298 K. 1 2 [Turn over page 06 MARKS DO NOT WRITE IN THIS MARGIN 1. (continued) (c) Another compound of chlorine, silver(I) chloride, forms an equilibrium mixture with excess chloride ions. AgCl(s)  +  Cl−(aq)  ∏  AgCl2 −(aq)      ∆G° = 25·6 kJ mol−1 at 298 K ∆G° and the equilibrium constant, K, are related as shown. ∆G ° = −2·30 RT log10 K R = 8·31 × 10−3 kJ K−1 mol−1 T = Temperature in Kelvin Use this information to calculate the equilibrium constant, K, for this reaction. 2 page 07 MARKS DO NOT WRITE IN THIS MARGIN 2. Reaction kinetics can be used to determine the order and mechanism of chemical reactions. A proposed mechanism for the reaction between hydrogen peroxide, H2O2(aq), and iodide ions, I−(aq), is shown below. Step 1 H2O2(aq) + I−(aq) ↓IO−(aq) + H2O(ℓ) slow Step 2 IO−(aq) + H3O+(aq) ↓HIO(aq) + H2O(ℓ) fast Step 3 HIO(aq) + H3O+(aq) + I−(aq) ↓ I2(aq) + 2H2O(ℓ) fast (a) State what is meant by the order of a reaction. (b) (i) Determine the overall order of reaction for the mechanism above. (ii) Write the rate equation for this reaction. (c) Write a balanced equation for the overall reaction. 1 1 1 1 [Turn over page 08 MARKS DO NOT WRITE IN THIS MARGIN 3. Brass is a useful alloy of copper and zinc. To determine the percentage of copper in a brass screw, a student dissolved the screw in 20 cm3 of concentrated nitric acid and made the resulting solution up to 250 cm3 in a volumetric flask. Five standard solutions were prepared by diluting a 0·10 mol l−1 stock solution of copper(II) nitrate with deionised water. (a) One of the standard solutions had a concentration of 0·010 mol l−1. Describe fully how this 0·010 mol l−1 solution should be prepared in a 50 cm3 volumetric flask from the 0·10 mol l−1 stock solution. (b) The colorimeter was fitted with a suitable filter and set to zero using a reference sample. The absorbance of the five standard solutions was determined and a calibration graph was drawn. 0∙30 0∙00 0∙40 0∙10 0∙50 0∙20 0∙60 0∙70 0∙80 absorbance 0∙000 0∙010 0∙020 0∙030 0∙040 0∙050 0∙060 0∙070 0∙080 concentration of Cu2+ (mol l−1) (i) Name the substance that should be used to set the colorimeter to zero. 2 1 page 09 MARKS DO NOT WRITE IN THIS MARGIN 3. (b) (continued) (ii) The absorbance of the sample solution was 0·71. The sample solution was then diluted to decrease the concentration by half. The absorbance of this diluted solution was then measured. Explain why the sample solution was diluted. (iii) The mass of the screw was 1·43 g. The absorbance of the diluted solution was 0·34. Calculate the percentage by mass of copper in the screw. 1 3 [Turn over page 10 MARKS DO NOT WRITE IN THIS MARGIN 4. There are different definitions for acids and bases. (a) One definition for acids and bases was proposed by Johannes Brønsted and Thomas Lowry. (i) State the Brønsted-Lowry definition for a base. (ii) A solution of hydrogen peroxide consists of two acid-conjugate base pairs. H2O2(aq)  +  H2O(ℓ)  ∏  H3O+(aq)  +  HO2 −(aq) Complete the table to identify one of the acid-conjugate base pairs. Acid Conjugate base (b) Another definition for acids and bases was proposed by Gilbert Lewis. A Lewis acid is a substance that can accept a pair of non-bonding electrons. A Lewis base is a substance that can donate a pair of non‑bonding electrons. An example of a Lewis acid-base reaction is shown. B(OH)3(aq)  +  2H2O(ℓ)  ∏  [B(OH)4]−(aq)  +  H3O+(aq) Explain why this is a Lewis acid-base reaction. 1 1 1 page 11 MARKS DO NOT WRITE IN THIS MARGIN 4. (continued) (c) Acids can be classified as strong or weak. The table contains information about four acids. Name of acid Formula Ka at 298 K ethanoic CH3COOH 1·7 × 10−5 chloroethanoic CH2ClCOOH 1·6 × 10−3 dichloroethanoic CHCl2COOH 5·0 × 10−2 trichloroethanoic CCl3COOH 2·3 × 10−1 (i) Describe the relationship between the number of chlorine atoms in an acid molecule and the strength of the acid. (ii) 1·89 g of chloroethanoic acid was dissolved in deionised water and the solution was made up to 250 cm3 in a volumetric flask. (A) Calculate the concentration, in mol l−1, of the chloroethanoic acid solution. (B) Using your answer to (A) calculate the pH of the chloroethanoic acid solution. 1 1 2 [Turn over page 12 MARKS DO NOT WRITE IN THIS MARGIN 4. (continued) (d) The action of pH indicators and buffer solutions involves the chemistry of acids and bases. Using your knowledge of chemistry, discuss the role of acids and bases in pH indicators and buffer solutions. 3 page 13 MARKS DO NOT WRITE IN THIS MARGIN 5. Electron transitions are responsible for some of the properties of metals such as sodium, zinc and strontium, and their compounds. (a) The orange-yellow colour emitted by some fireworks is due to electron transitions in sodium. The colour is produced when excited electrons return to their ground state. State what caused the electrons to become excited. (b) A solution containing the complex ion [Zn(H2O)6]2+ is colourless. (i) State the name of this complex ion. (ii) Electron transitions involving the d-subshell can give rise to colour in transition metal complexes. Explain fully why a solution of the complex ion [Zn(H2O)6]2+ is colourless. 1 1 2 [Turn over page 14 MARKS DO NOT WRITE IN THIS MARGIN 5. (continued) (c) Photoelectron spectroscopy is a technique that provides information on electrons and energy levels in atoms. It uses electromagnetic radiation to eject electrons from an atom and measures the kinetic energy of these emitted electrons. (i) A sample of strontium was exposed to electromagnetic radiation with a frequency of 3·08 × 1017 s−1. Calculate the energy, in J, of this electromagnetic radiation. (ii) Binding energy, Eb, is the energy required to eject an electron from an atom. Binding energy is calculated in electron volts, eV, using the relationship Eb = E − Ek Eb = binding energy E = energy of electromagnetic radiation Ek = kinetic energy of electron emitted 1 Joule = 6·24 × 1018 eV An electron was emitted with a kinetic energy, Ek, of 1254 eV. Using your answer to part (i), calculate the binding energy, in eV, for this electron. 1 2 page 15 [Turn over for next question DO NOT WRITE ON THIS PAGE page 16 MARKS DO NOT WRITE IN THIS MARGIN 6. The concentration of ethanol in vodka can be determined by reacting the ethanol with excess acidified potassium dichromate solution. 20·0 cm3 of vodka was transferred to a 1 litre volumetric flask and made up to the mark with deionised water. 1·0 cm3 of the diluted vodka was pipetted into a conical flask. 25·0 cm3 of 0·010 mol l−1 acidified potassium dichromate was added to the conical flask. The conical flask was then stoppered and warmed until the reaction was complete. 3C2H5OH(aq) + 2Cr2O7 2−(aq) + 16H+(aq)  ↓  3CH3COOH(aq) + 4Cr3+(aq) + 11H2O(ℓ) It was found that 1·65 × 10−4 moles of dichromate ions were left unreacted. (a) Calculate the concentration of ethanol, in mol l−1, in the undiluted vodka. (b) Explain why the acidified potassium dichromate was added in excess. 3 1 page 17 MARKS DO NOT WRITE IN THIS MARGIN 6. (continued) (c) The experimentally determined value was higher than the actual concentration of ethanol in the vodka. Other than apparatus uncertainties and transfer errors, suggest a reason why the experimentally determined concentration of ethanol was higher. (d) Describe a suitable control experiment that could be used to validate this technique. 1 1 [Turn over page 18 MARKS DO NOT WRITE IN THIS MARGIN 7. Carmine is a red pigment formed in a precipitation reaction. O OH OH O O O O OH AI O O OH OH −O H2O O O OH OH OH OH HO O OH OH OH HO OH −O Ca2+ carmine (a) Carmine can be removed from the reaction mixture by filtration. Suggest how the filtration could be carried out to ensure fast separation. (b) The structure shown above contains both pi and sigma bonds. (i) Explain how a sigma bond is formed. (ii) A pi bond is formed as a result of sp2 hybridisation. Explain what is meant by sp2 hybridisation. 1 1 1 page 19 MARKS DO NOT WRITE IN THIS MARGIN 7. (continued) (c) Carmine contains a conjugated system. Explain fully how this conjugated system gives rise to the red colour of carmine. (d) The use of carmine as a dye was largely abandoned in the nineteenth century. One of the pigments used to replace carmine is alizarin. Alizarin can be extracted from the root of a plant using methanol. OH OH O O alizarin (i) Explain why methanol is a suitable solvent for this extraction. 2 1 [Turn over page 20 MARKS DO NOT WRITE IN THIS MARGIN 7. (d) (continued) (ii) The infrared spectrum of alizarin is shown below. 0 50 100 4000 3000 2000 1500 1000 500 wavenumber (cm−1) transmittance (%) (A) Explain the effect infrared radiation has on the bonds within molecules and how this allows different functional groups to be identified. (B) Circle a functional group in the structure below that is responsible for the peak at 3395 cm−1. (An additional diagram, if required, can be found on page 28.) OH OH O O 2 1 page 21 MARKS DO NOT WRITE IN THIS MARGIN 7. (d) (ii) continued (C) For the peak at 3395 cm−1 calculate (I) the wavelength, in metres (II) the energy, in kJ mol−1, associated with this wavelength. 1 2 [Turn over page 22 MARKS DO NOT WRITE IN THIS MARGIN 8. Benzene, cyclohexene and cyclohexane are cyclic hydrocarbons with six carbon atoms. Each hydrocarbon takes part in a wide variety of chemical reactions. Using your knowledge of chemistry, discuss the reactions of these hydrocarbons. 3 page 23 MARKS DO NOT WRITE IN THIS MARGIN 9. Ephedrine can be used to prevent low blood pressure. N OH H ephedrine (a) Ephedrine can exist as different optical isomers due to the presence of chiral centres. (i) Circle a chiral centre in the structure of ephedrine shown above. (An additional diagram, if required, can be found on page 28.) (ii) State what is meant by the term optical isomers. 1 1 [Turn over page 24 MARKS DO NOT WRITE IN THIS MARGIN 9. (continued) (b) The psychoactive substance cathinone has a similar structure to ephedrine and can be synthesised under certain conditions in two steps as shown. O O Br O O NH Br 2 Step 1 Step 2 1-phenylpropanone, GFM = 134 g cathinone, GFM = 149 g Br2 NH3 (i) Suggest the type of chemical reaction taking place in Step 2 of the synthesis. (ii) Calculate the mass of cathinone produced from 9∙50 g of 1-phenylpropanone, assuming a percentage yield of 71∙8%. 1 3 page 25 MARKS DO NOT WRITE IN THIS MARGIN 10. Compound X can be added to petrol to make it burn more smoothly. H3C C CH3 CH3 CH3 O compound X (a) Compound X belongs to a class of organic compounds. Name this class of organic compounds. (b) (i) Draw a skeletal structural formula for compound X. (ii) Write the systematic name for compound X. 1 1 1 [Turn over page 26 MARKS DO NOT WRITE IN THIS MARGIN 10. (continued) (c) Compound X can be produced by reacting 2-chloromethylpropane with methoxide ions. C H3C CH3 Cl CH3 H3C O− H3C C CH3 CH3 O CH3 + compound X 2-chloromethylpropane methoxide ion (i) Methoxide ions can be produced by reacting sodium with a reagent. Name the reagent. (ii) The reaction between 2-chloromethylpropane and methoxide ions proceeds by an SN1 mechanism involving a carbocation intermediate. Using structural formulae and curly arrow notation, outline the mechanism for this reaction. (iii) Suggest why this reaction is more likely to proceed by an SN1 mechanism rather than an SN2 mechanism. 1 2 1 page 27 MARKS DO NOT WRITE IN THIS MARGIN 10. (continued) (d) Compound X is not optically active. Draw an isomer of compound X that is optically active. (e) The low resolution 1H NMR spectrum for compound X shown below is incomplete. Complete the spectrum by drawing one line to show the correct chemical shift and relative intensity for the other hydrogen environment. (An additional diagram, if required, can be found on page 29.) 10 9 8 7 6 5 4 3 2 1 0 TMS relative intensity chemical shift (ppm) 11 [END OF QUESTION PAPER] 1 2 page 28 MARKS DO NOT WRITE IN THIS MARGIN ADDITIONAL DIAGRAM FOR USE IN QUESTION 1 (a) 2p 1s 2s 3s 3p ADDITIONAL DIAGRAM FOR USE IN QUESTION 7 (d) (ii) B OH OH O O ADDITIONAL DIAGRAM FOR USE IN QUESTION 9 (a) (i) N OH H ephedrine page 29 MARKS DO NOT WRITE IN THIS MARGIN ADDITIONAL DIAGRAM FOR USE IN QUESTION 10 (e) 10 9 8 7 6 5 4 3 2 1 0 TMS relative intensity chemical shift (ppm) 11 page 30 MARKS DO NOT WRITE IN THIS MARGIN ADDITIONAL SPACE FOR ANSWERS AND ROUGH WORK page 31 MARKS DO NOT WRITE IN THIS MARGIN ADDITIONAL SPACE FOR ANSWERS AND ROUGH WORK page 32 [BLANK PAGE] DO NOT WRITE ON THIS PAGE