(a) Ethanol can be manufactured by two different methods.
Method 1: Fermentation of a sugar, \( \mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6 \):
\[ \mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6 \rightarrow 2 \mathrm{C}_2 \mathrm{H}_5 \mathrm{OH} + 2 \mathrm{CO}_2 \]
Method 2: Reaction of ethene with steam:
\[ \mathrm{C}_2 \mathrm{H}_4 + \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{C}_2 \mathrm{H}_5 \mathrm{OH} \]
(i) Give one advantage of using fermentation compared with Method 2.
(ii) Give one disadvantage of using fermentation compared with Method 2.
(b) Ethanol reacts with acidified potassium manganate(VII) to form water and a product that turns litmus red.
(i) State the name of the product that turns the litmus red.
(ii) State the type of reaction that ethanol undergoes.
(c) Ethanol reacts with methanoic acid to form an ester.
(i) Name the ester formed in this reaction.
(ii) Draw the structure of the ester formed. Show all of the atoms and all of the bonds.
(d) The table shows the melting points of ethanol and sodium chloride.
The difference in melting points is due to differences in attractive forces between particles in these substances.
Name the type of attractive force in each substance, which is responsible for the difference in melting points.
▶️ Answer/Explanation
(a) (i) Advantage of fermentation: The raw material (sugar, \( \mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6 \)) is renewable/sustainable, unlike ethene which is derived from crude oil.
(a) (ii) Disadvantage of fermentation: It is a slower process compared to the industrial hydration of ethene.
(b) (i) The product that turns litmus red is ethanoic acid (acetic acid), formed by the oxidation of ethanol.
(b) (ii) The reaction is an oxidation reaction, as ethanol loses hydrogen and gains oxygen.
(c) (i) The ester formed is ethyl methanoate (ethanol + methanoic acid → ethyl methanoate + water).
(c) (ii) The structure of ethyl methanoate is:
(d) The attractive forces are:
– Ethanol: Weak intermolecular forces (hydrogen bonding and van der Waals forces) between molecules.
– Sodium chloride: Strong ionic bonds between positive (\( \mathrm{Na}^+ \)) and negative (\( \mathrm{Cl}^- \)) ions.
Ethanol is manufactured by two different processes.
(a) For each process, name the organic reactant and state the type of reaction.
(b) Alcohols can be oxidised to form carboxylic acids.
Name a suitable oxidising agent for this reaction.
(c) Alcohols can be partially oxidised to form aldehydes.
Aldehydes are a homologous series of organic compounds.
Partial oxidation is achieved by reacting an alcohol with the oxidising agent in distillation apparatus as shown.
(i) Name apparatus A.
(ii) On the diagram, use one arrow to show where water enters apparatus A.
(d) The table shows some information about aldehydes.
(i) Complete the table.
(ii) Deduce the general formula of aldehydes.
(e) The structural formula of ethanal is shown.
The C=O group in aldehydes is at the end of the carbon chain.
This is a reactive part of the molecule.
(i) What is the name given to the reactive part of any organic molecule?
(ii) Complete the dot-and-cross diagram to show the electron arrangement of a molecule of ethanal. Inner shells have been drawn.
(f) Propanone belongs to a homologous series called ketones. Ketones have the same \(\text{C=O}\) group as aldehydes but the \(\text{C=O}\) group is not at the end of the carbon chain. Propanone has the same molecular formula as propanal, \(\text{C}_3\text{H}_6\text{O}\).
(i) What term is used to describe molecules with different structures but with the same molecular formula?
(ii) Suggest the structure of propanone, \(\text{C}_3\text{H}_6\text{O}\). Show all of the atoms and all of the bonds.
▶️ Answer/Explanation
(a) The two processes for ethanol production are:
1. Sugar(s) (organic reactant) → Fermentation (type of reaction).
2. Ethene (organic reactant) → Hydration (type of reaction).
(b) A suitable oxidising agent is acidified potassium manganate(VII) (oxidises alcohols to carboxylic acids).
(c) (i) Apparatus A is a Liebig condenser (cools vapours to liquids).
(ii) Water enters at the lower inlet (arrow should point to the bottom opening).
(d) (i) The table should be completed as:
– First row: Methanal (simplest aldehyde).
– Second row: \(\text{C}_4\text{H}_8\text{O}\) (butanal’s molecular formula).
(ii) The general formula for aldehydes is \(\text{C}_n\text{H}_{2n}\text{O}\).
(e) (i) The reactive part is called the functional group (determines chemical properties).
(ii) The dot-and-cross diagram for ethanal should show:
– 4 \(\text{C-H}\) bonds (shared electron pairs).
– 1 \(\text{C-C}\) bond.
– 1 \(\text{C=O}\) double bond (with lone pairs on oxygen).
(f) (i) Molecules with the same formula but different structures are structural isomers.
(ii) Propanone’s structure:
\(\text{CH}_3-\text{CO}-\text{CH}_3\) (C=O group on the middle carbon).