12. (a) When ethene is passed into aqueous chlorine one of the products is 2-chloroethanol. (i) The presence of a C–Cl bond in this compound can be shown by a simple test tube reaction. Outline the practical steps that are used in this method. You can assume that 2-chloroethanol is soluble in water. [4] (ii) The oxidation of 2-chloroethanol (Mr 80.6) produces chloroethanoic acid together with a little chloroethanal. (A410U20-1) Turn over. 21 Examiner only © WJEC CBAC Ltd. C C OH Cl H H H H 5.80 g of chloroethanol were oxidised and the chloroethanoic acid in the resulting mixture reacted with 0.0600 mol of sodium hydroxide in a 1:1 stoichiometric ratio. Show that the percentage conversion to chloroethanoic acid was 83 %. [3] C O OH ClCH2 C H H OH ClCH2 Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl H 22 (A410U20-1) Examiner only © WJEC CBAC Ltd. (b) DDT is an effective insecticide but its use in recent years has become restricted because of its persistence in the environment. The DDT that is sold is a mixture of closely related compounds that includes DDT, DDE and DDD. (i) Suggest why DDT is largely insoluble in water. [1] (ii) Suggest suitable reagent(s) that can be used to convert DDE into DDD. [1] DDT DDE DDD (A410U20-1) Turn over. Examiner only © WJEC CBAC Ltd. 11.0 11.4 11.8 12.2 9 10 13 48 Relative abundance Retention time / minutes (iii) Many areas around former DDT manufacturing sites remain contaminated. The soil from one contaminated area was analysed by gas chromatography. Calibration of the chromatogram showed that the concentration of DDT in the sample (shown as the largest peak) was 0.018 mol kg−1. Calculate the total concentration of all the contaminants shown in the chromatogram in mol kg−1. [2] Total concentration = ...................................................................... mol kg−1 23 24 (A410U20-1) Examiner only (c) Over the last thirty years the production and use of CFCs has declined mainly because of their adverse environmental effects. Using fluorotrichloromethane as your example, outline how the compound causes a reduction in the amount of ozone present in the upper atmosphere and state two problems that can be caused by this reduction. [6 QER] © WJEC CBAC Ltd. C C Cl F F F F F State and explain what you would expect to see in the molecular ion region of its mass spectrum and in its 13C spectrum. [4] 21 (A410U20-1) Turn over. 25 © WJEC CBAC Ltd. (d) The formula of chloropentafluoroethane is shown below. Examiner only 26 (A410U20-1) Examiner only © WJEC CBAC Ltd. 13. (a) 2,3-Dihydroxypropanal (glyceraldehyde), HOCH2CH(OH)CHO, contains a chiral centre. (i) State what is meant by a chiral centre. [1] (ii) Draw the two mirror image forms of 2,3-dihydroxypropanal. [1] (b) Glucose, like 2,3-dihydroxypropanal, contains an aldehyde group. Fehling’s / Benedict’s solutions are used to show the presence of an aldehyde. Describe another simple test to show the presence of this group. You should include the reagent(s) used and any observations made. [2] (A410U20-1) Turn over. 27 Examiner only © WJEC CBAC Ltd. (c) Glucose occurs as two enantiomers. The concentration of an enantiomer can be found by using a polarimeter to measure the rotation of the plane of plane polarised light. In an experiment using an aqueous solution of D-glucose at a certain temperature, the initial rotation of the plane of plane polarised light was 20 ° using a cell of 1 dm length to hold the glucose solution. Use the formula below to calculate the concentration of glucose in the solution in g dm−3. [2] [αD] = r × v m where specific rotation at this temperature [αD] = 112 ° rotation of the plane of plane polarised light (r) = 20 ° volume of solution in 1 dm cell (v) = 15 cm3 m is the mass of glucose in 15 cm3 of solution Concentration = ...................................................................... g dm−3 (d) Butan-2-ol (Mr 74) can be dehydrated to but-1-ene and but-2-ene. CH3CH2CH(OH)CH3 CH3CH2CH=CH2 + CH3CH=CHCH3 around 30 % around 70 % (i) State a dehydrating agent for this reaction. [1] (ii) Both but-2-ene and penta-1,3-diene can exist as E-Z isomers. Explain why this type of isomerism occurs and give the displayed formula of E-penta-1,3-diene. [2] 28 (A410U20-1) © WJEC CBAC Ltd. (e) Compound R is a neutral saturated aliphatic compound that contains only carbon, hydrogen and oxygen. The percentage of oxygen by mass is 24.6. This compound is hydrolysed in acid solution to give two new organic compounds, S and T. Further information about R, S and T is given below. Compound R • The 13C NMR spectrum shows that there are five different carbon environments • The 1H NMR spectrum shows the following signals • The infrared absorption spectrum shows a peak at 1731 cm−1 but no peak at 2500–3550 cm−1 • It is not an aldehyde or a ketone Compound S • The 13C NMR spectrum shows that there are three different carbon environments • The 1H NMR spectrum shows the following signals Signal δ / ppm Relative peak area 1.20 singlet 9 1.25 triplet 3 4.11 quartet 2 Signal δ / ppm Relative peak area 1.20 singlet 9 around 11 1 • An aqueous solution is weakly acidic Compound T • The 13C NMR spectrum shows that there are two different carbon environments • The 1H NMR spectrum is shown below – relative peak areas 1, 2 and 3 δ / ppm 10 8 6 4 2 0 1 2 3 • The compound is neutral (A410U20-1) Turn over. 29 Examiner only © WJEC CBAC Ltd. Use this information to deduce the formulae of compounds S and T and hence the displayed formula of compound R. It is not necessary to name any of the compounds. [11] END OF PAPER 20 30 (A410U20-1) Examiner only © WJEC CBAC Ltd. For continuation only. Examiner only (A410U20-1) 31 © WJEC CBAC Ltd.