page 13 25. Alkenes react with ozone, O3, to form ozonides which can be decomposed to give carbonyl compounds. C C H C2H5 O3 H H C O C O + H C2H5 H H decomposition an ozonide Which of the following alkenes would produce a mixture of ethanal and propanone? CH3CH=CHCH2CH3 CH3CH=CHCH3 CH3C=CH2 CH3 CH3CH=CCH3 CH3 A C D B [END OF QUESTION PAPER] page 14 SPACE FOR ROUGH WORK page 15 SPACE FOR ROUGH WORK page 16 [BLANK PAGE] DO NOT WRITE ON THIS PAGE H 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 Instructions for the completion of Paper 1 are given on page 02. Record your answers on the answer grid on page 03. Use blue or black ink. Before leaving the examination room you must give your answer booklet to the Invigilator; if you do not, you may lose all the marks for this paper. X813/76/02 Chemistry Paper 1 — Multiple choice Answer booklet FRIDAY, 10 MAY 9:00 AM – 9:40 AM A/PB page 02 Paper 1 — 25 marks The questions for Paper 1 are contained in the question paper X813/76/12. Read these and record your answers on the answer grid on page 03. 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 space for rough work at the end of the question paper X813/76/12. 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 Paper 1 — Answer grid A B C D 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Chemistry page 04 [BLANK PAGE] DO NOT WRITE ON THIS PAGE H 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 Total marks — 95 Attempt ALL questions. You may use a calculator. You may refer to the Chemistry Data Booklet for Higher and Advanced Higher. 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. 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. X813/76/01 FRIDAY, 10 MAY 10:10 AM – 12:30 PM A/PB Chemistry Paper 2 page 02 MARKS DO NOT WRITE IN THIS MARGIN Total marks — 95 Attempt ALL questions 1. Sodium thiosulfate, Na2S2O3, can be used to investigate the effect of reaction conditions on the rate of reaction. (a) Sodium thiosulfate solution reacts with hydrochloric acid to form a precipitate of solid sulfur. By placing the reaction mixture in a conical flask over a cross and recording the time taken for the cross to disappear, the effect of changing the reaction conditions can be investigated. sodium thiosulfate and water a cross drawn on paper stop timing when the cross disappears add 5∙0 cm3 hydrochloric acid and start timing (i) The equation for the reaction is Na2S2O3(aq) + HCl(aq) ↓ S(s) + SO2(g) + NaCl(aq) + H2O(ℓ) Balance the equation. 1 page 03 MARKS DO NOT WRITE IN THIS MARGIN 1. (a) (continued) (ii) In one set of experiments, the effect of varying the concentration of sodium thiosulfate was investigated. Experiment Volume of 0·15 mol l-1 Na2S2O3 (cm3) Volume of water (cm3) Rate (s-1) A 50 0 0·0454 B 40 0·0370 C 30 0·0285 D 20 0·0169 E 10 40 0·0063 (A) Complete the table to show the volumes of water that would have been used to vary the concentration of sodium thiosulfate. (B) Calculate the time, in seconds, for the cross to disappear in experiment C. [Turn over 1 1 page 04 MARKS DO NOT WRITE IN THIS MARGIN 1. (a) (continued) (iii) The reaction can also be used to investigate the effect of changing temperature on the rate of reaction. The results from an investigation are shown in the graph below. 80 40 0 0∙08 0∙14 0∙06 0∙12 0∙04 0∙10 0∙02 0∙00 temperature (°C) relative rate (s-1) 70 30 60 20 50 10 Use the graph to determine the temperature rise, in °C, required to double the rate of the reaction. (b) Collision theory states that for particles to react they must first collide with each other. State two conditions necessary for the collisions to result in the formation of products. 1 2 page 05 MARKS DO NOT WRITE IN THIS MARGIN 1. (continued) (c) Sodium thiosulfate also reacts with iron(III) nitrate. The potential energy diagram below shows the change in potential energy during the reaction carried out without a catalyst. potential energy (kJ mol-1) reaction pathway (i) Draw an X on the potential energy diagram above to show where the activated complex is formed. (An additional diagram, if required, can be found on page 41). (ii) Cu2+ ions catalyse the reaction. Add a dotted line to the diagram to show the change in potential energy with the catalyst. (An additional diagram, if required, can be found on page 41). [Turn over 1 1 page 06 MARKS DO NOT WRITE IN THIS MARGIN 2. 2019 is the 150th anniversary of the periodic table’s creation by Dmitri Mendeleev. The patterns identified by Mendeleev form the basis of the modern periodic table. The major periodic trends include ionisation energy and covalent radius. (a) The first ionisation energies of elements with atomic number 1 to 20 are shown in the graph. K Ar Ne He Na Li H atomic number ionisation energy (kJ mol-1) 20 15 10 5 0 2500 2000 1500 1000 500 0 (i) Explain why the first ionisation energy shows an increase going from lithium to neon. (ii) Explain why the first ionisation energy of potassium is less than the first ionisation energy of lithium. 1 1 page 07 MARKS DO NOT WRITE IN THIS MARGIN 2. (continued) (b) A graph showing the ionisation energies for nitrogen is shown. 7 6 5 4 3 2 1 0 70000 60000 50000 40000 30000 20000 10000 0 ionisation energy (kJ mol-1) ionisation energy number (i) Write the equation for the second ionisation energy of nitrogen. (ii) Explain fully the increase between the 5th and 6th ionisation energies of nitrogen. [Turn over 1 2 page 08 MARKS DO NOT WRITE IN THIS MARGIN 2. (continued) (c) Ionic radius is a measure of the size of an ion. Explain fully why the ionic radius of phosphorus is greater than the ionic radius of aluminium. 2 page 09 MARKS DO NOT WRITE IN THIS MARGIN 2. (continued) (d) The structure of an ionic compound consists of a giant lattice of oppositely charged ions. The arrangement of ions is determined by the ‘radius ratio’ of the ions involved. radius of positive ion radius ratio radius of negative ion = Na+ ion Cl- ion radius ratio = 0·52 Key sodium chloride Cs+ ion Cl- ion radius ratio = 0·96 Key caesium chloride By using the table of ionic radii on page 17 of the data booklet, predict whether the structure of barium oxide, BaO, is similar to caesium chloride or sodium chloride. Your answer must include a calculated radius ratio. 1 [Turn over page 10 MARKS DO NOT WRITE IN THIS MARGIN 3. The melting point of non-metal elements depends on structure and bonding. Using your knowledge of chemistry, comment on this statement. 3 page 11 MARKS DO NOT WRITE IN THIS MARGIN 4. Cider is made from apples in a process that involves crushing and pressing the apples, converting the sugars into alcohol, maturing and bottling. (a) Brewers add yeast, which contains a mixture of enzymes to convert the sugars in the apples into alcohol and carbon dioxide. (i) State what is meant by the term enzyme. (ii) The % mass of alcohol in the cider can be calculated using the formula mass of alcohol % mass of alcohol 100 mass of cider = × A 50·0 cm3 sample of cider was found to contain 3·05 g of alcohol. 1·0 cm3 of the cider weighed 1·36 g. Calculate the % mass of alcohol in the cider. (b) During the maturing process malic acid is converted to lactic acid and another product. lactic acid malic acid H C 3 HO OH CH2 C CH C CH C OH O O O OH OH X + (i) Name compound X. 1 1 1 [Turn over page 12 DO NOT WRITE IN THIS MARGIN 4. (b) (continued) (ii) The maturing process in cider samples can be monitored using thin layer chromatography. Samples of lactic acid, malic acid and ciders A, B, C, and D are spotted on a silica plate and the solvent allowed to travel up the plate. The chromatogram obtained is shown below. 6 5 4 3 2 1 sample applied solvent direction of movement of solvent distance moved by solvent = 16·4 cm Number Sample applied Distance moved by spot(s) (cm) 1 lactic acid 8·2 2 malic acid 4·1 3 cider A 4·1, 8·2 4 cider B 8·2 5 cider C 4·1 6 cider D 4·1, 8·2 page 13 MARKS DO NOT WRITE IN THIS MARGIN 4. (b) (ii) (continued) The retention factor, Rf, for a substance can be a useful method of identifying the substance. f distance moved by the substance R distance moved by the solvent = (A) Calculate the Rf value of malic acid. (B) The maturing process is complete when all of the malic acid has been converted to lactic acid. The cider is now ready to be bottled. Use the chromatogram to determine which cider is ready to be bottled. [Turn over 1 1 page 14 MARKS DO NOT WRITE IN THIS MARGIN 4. (continued) (c) Glycerol can be added to cider before bottling to produce a sweeter tasting cider. State the systematic name for glycerol. (d) Cider contains many naturally occurring compounds that affect taste and aroma. (i) Procyanidin B2 provides a bitter taste to cider. procyanidin B2 CH C HO C C C CH CH O CH C OH OH OH C C CH HC OH 2 HC CH CH C HO C C C C CH O CH C OH OH OH C C CH HC OH HC CH Explain fully why procyanidin B2 is water soluble. 1 2 page 15 MARKS DO NOT WRITE IN THIS MARGIN 4. (d) (continued) (ii) Cider smells of apples because it contains ethyl 2-methylbutanoate. C H H H C H C H CH3 H O C C H O H H H C H ethyl 2-methylbutanoate Name the carboxylic acid used to make ethyl 2-methylbutanoate. (iii) Farnesene is a terpene responsible for the ripe apple aroma of cider. H C 3 C 2 2 CH CH CH 3 CH 3 CH 3 CH CH 2 C CH 2 CH CH CH C farnesene Name the molecule on which terpenes are based. (e) Ethanol in cider can be oxidised to ethanal, spoiling the aroma. ethanal H3C H C O (i) Name the functional group circled in the ethanal molecule. (ii) Further oxidation of ethanal can produce another product that spoils the flavour of cider. Name this product. 1 1 1 1 [Turn over page 16 MARKS DO NOT WRITE IN THIS MARGIN 5. The combustion reactions of methane and heptane can be studied in different ways. (a) The combustion of methane produces carbon dioxide and water vapour when carried out at temperatures above 100 °C. CH4(g) + 2O2(g) ↓ CO2(g) + 2H2O(g) (i) Using bond enthalpies and mean bond enthalpies from the data booklet, calculate the enthalpy change, in kJ mol-1, for this reaction. (ii) Explain the difference between bond enthalpy and mean bond enthalpy. 2 1 page 17 MARKS DO NOT WRITE IN THIS MARGIN 5. (a) (continued) (iii) Calculate the mass, in g, of carbon dioxide produced by combustion of 200 cm3 methane in excess oxygen. Take the volume of 1 mole of methane gas to be 24 litres. CH4(g) + 2O2(g) ↓ CO2(g) + 2H2O(g) GFM = 44·0 g [Turn over 2 page 18 MARKS DO NOT WRITE IN THIS MARGIN 5. (continued) (b) The enthalpy of combustion of heptane, C7H16, can be determined using a calorimeter. thermometer draught shield container water heptane burner The following results were obtained. Mass of heptane burned (g) 1·1 Mass of 1 mole of heptane (g) 100·0 Volume of water used (cm3) 400 Initial temperature of water (°C) 26 Final temperature of water (°C) 49 (i) State the measurements required to calculate the mass of heptane burned in this experiment. 1 page 19 MARKS DO NOT WRITE IN THIS MARGIN 5. (b) (continued) (ii) Calculate the enthalpy of combustion, in kJ mol-1, for heptane from the experimental results given. (iii) The theoretical value for the enthalpy of combustion of heptane is significantly higher than the experimental value. Suggest why the experimental value is different to the theoretical value. [Turn over 3 1 page 20 MARKS DO NOT WRITE IN THIS MARGIN 6. Thiols are compounds that contain an –SH functional group. They often have very strong, unpleasant odours. (a) Ethanethiol is used to add a smell to gaseous fuels in order to give warnings of gas leaks. H C H H C H H S H ethanethiol (i) A student used the boiling points of ethanethiol and propan-1-ol to compare the strength of intermolecular forces. H C H H C H H S H H C H H C H H C O H H H propan-1-ol boiling point = 97 °C ethanethiol boiling point = 35 °C (A) State the reason why propan-1-ol was a suitable alcohol to compare with ethanethiol. (B) Explain why propan-1-ol has a higher boiling point than ethanethiol. Your answer should include the names of the intermolecular forces broken when each liquid boils. 1 2 page 21 MARKS DO NOT WRITE IN THIS MARGIN 6. (a) (continued) (ii) Name the thiol that contains only one carbon atom. (iii) The minimum concentration of ethanethiol in air that can be detected by humans is 2·7 × 10-7 mg per cm3 of air. Calculate the minimum mass of ethanethiol that needs to be present in a room containing 43 900 litres of air in order for it to be detected. (b) 2-methyl-2-propanethiol is also used to add a smell to gaseous fuels. H C H H C SH CH3 C H H H 2-methyl-2-propanethiol (i) Suggest why 2-methyl-2-propanethiol is classified as a tertiary thiol. [Turn over 1 2 1 page 22 MARKS DO NOT WRITE IN THIS MARGIN 6. (b) (continued) (ii) Thiols can be made by the addition of hydrogen sulfide to alkenes. 2-methyl-2-propanethiol can be made by the addition reaction shown. H C H H C CH3 CH3 C H H S H H H C H H C SH C H H H + 2-methyl-2-propanethiol GFM = 90·1 g 2-methylpropene GFM = 56·0 g (A) Draw the structure for the other isomer formed in this addition reaction. (B) A chemist obtained an 84% yield of 2-methyl-2-propanethiol after starting with 30·5 g of 2-methylpropene. Calculate the mass, in g, of 2-methyl-2-propanethiol made by the chemist. 1 2 page 23 MARKS DO NOT WRITE IN THIS MARGIN 7. Esters can be synthetic or natural. (a) The synthetic polyester PET, poly(ethylene terephthalate), has many ester links. PET can break down by a free radical reaction. One of the steps involved in breaking down PET is shown. C C C C O C C O C C C H H C O O O O• H C C O O H H H H C C C C C C H O H H H C C C + C C C O C C C H C O O O• H C O C O O H H H H C C C C C C H O O H H H H (i) State the name for this step. (ii) Name the component of sunlight that can cause plastics such as PET to break down. (iii) Name the type of substance that can be added to plastics to prevent them breaking down in this way. [Turn over 1 1 1 page 24 MARKS DO NOT WRITE IN THIS MARGIN 7. (continued) (b) (i) Natural cyclic esters called lactones can be formed from hydroxycarboxylic acids. 5-hydroxypentanoic acid is a hydroxycarboxylic acid that when heated, with dilute acid, will form a cyclic ester. HO C OH O CH2 CH2 CH2 CH2 H2C H2C CH2 CH2 C O O Y + Name product Y in this reaction. (ii) Draw the structure for the cyclic compound formed when 4-hydroxypentanoic acid is heated with dilute acid. C OH O OH CH CH2 CH2 H3C 4-hydroxypentanoic acid 1 1 page 25 MARKS DO NOT WRITE IN THIS MARGIN 7. (b) (continued) (iii) Name the hydroxycarboxylic acid shown below. H3C CH CH2 C OH C O OH [Turn over 1 page 26 MARKS DO NOT WRITE IN THIS MARGIN 8. Gelatin is a soluble protein that can be added to different food products. (a) A structure for a section of a protein chain in gelatin is shown. N C C H H N O C H C H H O N H2C CH2 CH2 CH C N O H CH CH2 C O N H C H H C O N H C H CH2 C O CH2 C O OH CH2 CH2 NH C NH2 NH CH3 (i) State the number of amino acids that joined together to form the section of the protein chain shown. (ii) Name the weakest van der Waals’ force between water and gelatin molecules. (b) A student was investigating the viscosity of different concentrations of gelatin solution. (i) The student was asked to prepare a 2% gelatin solution, which is a solution that contains 2 g of gelatin per 100 cm3 of solution. The student prepared this solution by adding 100 cm3 of distilled water into a volumetric flask, then adding 2 g of gelatin. Describe how the student should have made up the solution. 1 1 3 page 27 MARKS DO NOT WRITE IN THIS MARGIN 8. (b) (continued) (ii) The results obtained from the student’s viscosity experiment are shown. Concentration of gelatin solution (%) Viscosity (units) 2·0 1·0 4·0 2·0 6·0 4·0 8·0 7·0 10·0 Predict the student’s result for the viscosity, in units, of a 10·0% gelatin solution. (c) Bromelain is a mixture of enzymes found in pineapple that aid digestion. (i) Adding raw pineapple to gelatin results in the gelatin molecules being hydrolysed. The rate of hydrolysis is reduced if the pineapple is cooked. Explain why the rate of hydrolysis is reduced. (ii) Bromelain can be purchased as tablets that contain 500 mg of bromelain. The flesh from a pineapple contains 13·2 mg of bromelain per gram. Calculate the mass, in g, of this pineapple that would be needed to provide 500 mg of bromelain. [Turn over 1 1 1 page 28 MARKS DO NOT WRITE IN THIS MARGIN 9. Chlorine is used in the production of many other chemicals. (a) Chlorine can be produced by the reaction of hydrogen chloride with air using the Deacon process. 4HCl(g) + O2(g) Ý 2Cl2(g) + 2H2O(g) 250 150 50 -50 reaction pathway -100 -150 potential energy (kJ mol-1) 0 100 200 (i) Using the potential energy diagram, determine the activation energy, in kJ mol-1, for the forward reaction. (ii) Explain why increasing the temperature in the Deacon process results in less chlorine being produced. 1 1 page 29 MARKS DO NOT WRITE IN THIS MARGIN 9. (continued) (b) One laboratory method for the preparation of chlorine gas involves adding concentrated hydrochloric acid to potassium permanganate. The chlorine gas produced also contains small amounts of hydrogen chloride gas. To remove the hydrogen chloride gas the gases are bubbled through water. Finally, insoluble chlorine gas is collected. potassium permanganate concentrated hydrochloric acid Complete a labelled diagram to show an apparatus suitable for carrying out this preparation. (An additional diagram, if required, can be found on page 41) [Turn over 2 page 30 MARKS DO NOT WRITE IN THIS MARGIN 9. (continued) (c) Carbon tetrachloride, CCl4, is prepared by the reaction of chlorine gas, Cl2, with methane, CH4. CH4(g) + 4Cl2(g) ↓ CCl4(g) + 4HCl(g) Calculate the enthalpy change, in kJ mol−1, for this reaction using the following information. C(s) + 2H2(g) ↓ CH4(g) ΔH = -75 kJ mol-1 C(s) + 2Cl2(g) ↓ CCl4(g) ΔH = -98 kJ mol-1 1 2H2(g) + 1 2Cl2(g) ↓ HCl(g) ΔH = -92 kJ mol-1 2 page 31 [Turn over for next question DO NOT WRITE ON THIS PAGE page 32 MARKS DO NOT WRITE IN THIS MARGIN 10. A student investigated the purity of a sample of magnesium chloride, MgCl2. The sample was dissolved in water and then an excess of silver nitrate, AgNO3, was added to produce a precipitate of silver chloride, AgCl. The precipitate was collected, dried and weighed. MgCl2(aq) + 2AgNO3(aq) ↓ 2AgCl(s) + Mg(NO3)2(aq) (a) The student prepared the magnesium chloride solution by dissolving 2·503 g of impure magnesium chloride in water. Explain why the student should use distilled or deionised water, rather than tap water, when preparing the solution. (b) (i) Complete the table to show the most appropriate piece of apparatus that could be used to measure the required volumes. Measurement Apparatus 20·0 cm3 (accurately) 35 cm3 (approximately) (ii) The steps required to collect, dry and weigh the precipitate are listed below. However, the steps are in the wrong order. A. Weigh the precipitate and the filter paper B. Wash the precipitate with water to remove any impurities C. Filter the precipitate D. Dry the precipitate in an oven E. Weigh the filter paper Complete the flow chart below to show the correct order of steps the student should carry out to collect, dry and weigh the precipitate. last step E first step (An additional diagram, if required, can be found on page 41) 1 2 1 page 33 MARKS DO NOT WRITE IN THIS MARGIN 10. (b) (continued) (iii) 1·393 g of silver chloride precipitate was produced from the magnesium chloride solution. MgCl2(aq) + 2AgNO3(aq) ↓ 2AgCl(s) + Mg(NO3)2(aq) GFM = 95·3 g GFM = 143·4 g Calculate the mass of magnesium chloride, in g, present in the magnesium chloride solution. (c) The average mass of magnesium chloride in 2·503 g of the original impure sample was calculated to be 2·403 g. Calculate the % of magnesium chloride present in the original sample. [Turn over 2 1 page 34 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 11. Differences in physical and chemical properties can be used to distinguish one compound from another. The compounds extracted from orange juice include antioxidants, flavour molecules, essential oils, aroma molecules and coloured molecules. Some examples of these are shown below. H2C H2C CH CH2 CH C CH3 C H3C CH2 limonene O H HO C C H CH2OH CH2OH C OH OH H C fructose CH2 O C HC C C C O HO HO OH HO vitamin C C C C C C OH OH H H H H HO O O HO O C citric acid C C H H C H H H H C H H H C H H C C H H C H H H O octanal C C C H2C H2C CH CH CH CH C CH CH3 CH3 C CH CH C 3 CH3 CH3 CH3 CH3 CH3 CH3 CH2 CH CH2 CH2 CH2 CH CH C CH C CH CH CH CH C C H3C beta-carotene C O O C H H H C H H H C H H C C H H H H ethyl butanoate page 35 MARKS DO NOT WRITE IN THIS MARGIN 11. (continued) Using your knowledge of chemistry, comment on how the differences in physical and chemical properties can be used to distinguish between the compounds extracted from orange juice. [Turn over 3 page 36 DO NOT WRITE IN THIS MARGIN 12. The label from a bottle of pine fresh bleach cleaner is shown. PINE FRESH BLEACH CLEANER Formulated to kill germs and remove stains Ingredients: aqua, sodium hypochlorite, sodium hydroxide, less than 5% anionic surfactants, non-ionic surfactants, soap, perfume 6 000129 7103487 > WARNING! Do not use together with other products. May release dangerous gases (chlorine) DANGER Keep out of reach of children CORROSIVE (a) Surfactant molecules are added to bleach cleaner to act as detergents, soaps or emulsifiers. Information on three of the surfactants in the bleach cleaner is shown in the table. Surfactant structure Type of surfactant Head group H C 3 CH CH2 CH2 CH2 2 2 CH2 2 2 2 2 2 CH CH CH O CH 2 CH O CH CH H Compound A non-ionic polar H C 3 H C 3 NH3+Cl– CH2 CH2 CH2 2 2 CH2 2 2 2 2 2 CH CH CH CH CH 2 2 CH CH C CH 3 CH 3 CH CH CH Compound B O–Na+ O C H C 3 CH CH2 CH2 CH2 2 2 CH2 2 2 2 2 2 2 2 CH CH CH CH CH CH 2 2 2 CH CH CH CH CH Compound C ionic negatively charged page 37 MARKS DO NOT WRITE IN THIS MARGIN 12. (a) (continued) (i) Complete the table for compound B. (ii) Compound C is a soap molecule. (A) Soaps can be made from fats and oils. Name the reaction used to make soaps from fats and oils. (B) Soap molecules allow oil to mix with water. O–Na+ O C H C 3 CH CH2 CH2 CH2 2 2 CH2 2 2 2 2 2 2 2 CH CH CH CH CH CH 2 2 2 CH CH CH CH CH Compound C Explain fully the cleaning action of compound C. You may wish to use diagrams to illustrate your answers. [Turn over 1 1 3 page 38 MARKS DO NOT WRITE IN THIS MARGIN 12. (a) (continued) (iii) The structure of an emulsifier molecule is shown below. 2 H C 2 H C 2 O CH HO C O CH2 CH2 2 2 CH2 2 2 2 2 2 2 CH CH CH CH CH CH CH 2 2 2 CH CH CH CH CH CH 3 CH 2 CH OH State how emulsifiers are made from edible oils. (b) Sodium hypochlorite, Na+OCl-, is the main active compound in bleach. PINE FRESH BLEACH CLEANER Formulated to kill germs and remove stains Ingredients: aqua, sodium hypochlorite, sodium hydroxide, less than 5% anionic surfactants, non-ionic surfactants, soap, perfume 6 000129 7103487 > WARNING! Do not use together with other products. May release dangerous gases (chlorine) DANGER Keep out of reach of children CORROSIVE Sodium hypochlorite, Na+OCl-, is produced by reacting chlorine with sodium hydroxide solution. Cl2(g) + 2Na+OH-(aq) ↓ Na+OCl- (aq) + Na+Cl- (aq) + H2O(ℓ) (i) A chlorine molecule has a pure covalent bond. Explain what is meant by a pure covalent bond. 1 1 page 39 MARKS DO NOT WRITE IN THIS MARGIN 12. (b) (continued) (ii) When the chlorine is reacted with sodium hydroxide solution an excess of sodium hydroxide is used. Suggest why an excess of sodium hydroxide is used. (c) In the bleach cleaner an equilibrium exists. 2H+(aq) + OCl-(aq) + Cl- (aq) Ý Cl2(g) + H2O(ℓ) The label warns that the bleach cleaner should not be used with other products as it may release chlorine gas. Explain clearly why mixing the bleach with an acid would shift the equilibrium to the right, resulting in the release of chlorine gas from the bleach cleaner. [Turn over for next question 1 2 page 40 MARKS DO NOT WRITE IN THIS MARGIN 12. (continued) (d) The concentration of hypochlorite, OCl-, in bleach can be determined by a redox reaction that involves two steps. Step 1 An excess of acidified potassium iodide is added to the bleach. This converts the iodide ions into iodine. OCl-(aq) + 2I- (aq) + 2H+(aq) ↓ I2(aq) + Cl- (aq) + H2O(ℓ) Step 2 The iodine produced in step 1 is titrated with sodium thiosulfate, Na2S2O3. I2(aq) + 2Na2S2O3(aq) ↓ 2NaI(aq) + Na2S4O6(aq) (i) Write the ion-electron equation for the reduction reaction taking place in Step 1. (ii) A 25 cm3 sample of a diluted bleach was transferred into a conical flask and excess acidified potassium iodide added. The iodine produced was titrated with 0·098 mol l−1 Na2S2O3, requiring an average volume of 9·0 cm3 to reach the end point. Calculate the concentration, in mol l−1, of sodium hypochlorite in the diluted bleach. [END OF QUESTION PAPER] 1 3 page 41 MARKS DO NOT WRITE IN THIS MARGIN ADDITIONAL SPACE FOR ANSWERS AND ROUGH WORK Additional diagram for question 1 (c) potential energy (kJ mol-1) reaction pathway Additional diagram for question 9 (b) potassium permanganate concentrated hydrochloric acid Additional diagram for question 10 (b) (ii) last step E first step page 42 MARKS DO NOT WRITE IN THIS MARGIN ADDITIONAL SPACE FOR ANSWERS AND ROUGH WORK page 43 MARKS DO NOT WRITE IN THIS MARGIN ADDITIONAL SPACE FOR ANSWERS AND ROUGH WORK page 44 [BLANK PAGE] DO NOT WRITE ON THIS PAGE