Question 12
The oxidation of propan-1-ol can form propanal and propanoic acid.
The boiling points of these compounds are shown in the table.
In a preparation of propanal, propan-1-ol is added dropwise to the oxidising agent and the aldehyde is separated from the reaction mixture by distillation.
(a) Explain, with reference to intermolecular forces, why distillation allows propanal to be separated from the other organic compounds in this reaction mixture.
(3)
(b) Give two ways of maximising the yield of propanal obtained by distillation of the reaction mixture.
(2)
(c) Describe how you would carry out a simple test-tube reaction to confirm that the sample of propanal obtained by distillation does not contain any propanoic acid.
(2)
(d) A student carried out an experiment to determine the enthalpy of combustion of ethanol.
Combustion of 457 mg of ethanol increased the temperature of 150 g of water from 25.1 °C to 40.2 °C
Calculate a value, in kJ mol–1, for the enthalpy of combustion of ethanol in this experiment.
Give your answer to the appropriate number of significant figures.
(The specific heat capacity of water is 4.18 J K–1 g–1)
(3)
(e) A mixture of isomeric alkenes is produced when pentan-2-ol is dehydrated in the presence of hot concentrated sulfuric acid. Pent-1-ene is one of the isomers produced.
Name and outline a mechanism for the reaction producing pent-1-ene.
(4)
(f) A pair of stereoisomers is also formed in the reaction in part (e).
Name the less polar stereoisomer formed.
Explain how this type of stereoisomerism arises.
(2)
(Total 16 marks)