12 (B410U20-1) Examiner only 10. (a) A student is asked to prepare a sample of ethanal by oxidising ethanol. (i) Write an equation for this reaction. [1] Use [O] to represent the oxidising agent and show the structure of the organic product. (ii) Describe, giving brief experimental details, how he can carry out the reaction. [4] (iii) Ethanol can also be oxidised to ethanoic acid. Describe how the student could use a chemical test to confirm that his sample of ethanal did not contain ethanoic acid. [2] (b) State a difference and a similarity between the 13C NMR spectra of ethanal and ethanol. [2] Difference .................................................................................................................................................................................... ................................................................................................................................................................................................................ Similarity ....................................................................................................................................................................................... ................................................................................................................................................................................................................ © WJEC CBAC Ltd. (B410U20-1) Turn over. 13 Examiner only (c) Ethanol is widely used as a biofuel in some countries. (i) The equation for its combustion is given below. C2H5OH + 3O2 2CO2 + 3H2O Use the average bond enthalpy values given in the table below to calculate the enthalpy of combustion for ethanol. [3] © WJEC CBAC Ltd. ΔcH ethanol = ........................................................ kJ mol–1 (ii) Give a disadvantage of biofuels compared with fossil-based fuels. [1] (d) Ethanol and hexan-1-ol are both primary alcohols. Explain why ethanol is soluble in water but hexan-1-ol is not. [2] 15 Bond Average bond enthalpy / kJ mol–1 C—C 348 C—H 412 C—O 360 O—H 463 496 743 — — — — O O C O