(a)(i) State three characteristics of a homologous series.
(ii) Give the name and structural formula of the second member of the alkyne series.
(iii) Write an equation to represent the combustion of ethane in excess oxygen.
(b) Name the type of reaction involved in the conversion of ethanol to
(i) ethene;
(ii) ethylethanoate;
(iii) chloroethane;
(iv) ethoxide
(v) ethanoic acid
(c) Consider the following compound.
(i) Write its IUPAC name.
(ii) Give its molecular formula and empirical formula
(iii) List the products of its H H 0 reaction with saturated Na\(_2\)CO\(_3\) solution.
(iv) State with reason whether its boiling point will be higher or lower than that of the corresponding alkane.
(d) A vegetable oil X was treated with activated charcoal and then with a gas Y in the presence of a catalyst in order to manufacture
(i) Identify Y.
(ii) State the function of the activated charcoal.
(iii) What is the catalyst used?
(iv) If a sample of X is heated with concentrated sodium hydroxide solution, list the products that will be obtained.
(a)(i) Three characteristics of a homologous series.
- All members are represented by the same general formula (e.g. alkanes \(C_nH_{2n+2}\)).
- Successive members differ from the next by a \(-CH_2-\) unit (a relative molecular mass difference of 14).
- Members have similar chemical properties because they contain the same functional group.
- There is a gradual change in physical properties (e.g. boiling point rises steadily) as molar mass increases.
(Any three of the above.)
(a)(ii) Second member of the alkyne series.
Name: propyne. Structural formula: \(CH_3-C{\equiv}CH\).
(a)(iii) Combustion of ethane in excess oxygen.
\[2C_2H_{6(g)} + 7O_{2(g)} \rightarrow 4CO_{2(g)} + 6H_2O_{(l)}\]
(b) Type of reaction in the conversion of ethanol to:
- ethene: dehydration (an elimination reaction);
- ethyl ethanoate: esterification (a condensation reaction);
- chloroethane: substitution (halogenation, e.g. with \(PCl_5\) or conc. \(HCl\));
- ethoxide: redox / displacement (sodium displaces hydrogen: \(2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2\));
- ethanoic acid: oxidation.
(c) The compound shown is \(CH_3-CH_2-COOH\) (an ethyl group joined to a carboxyl, \(-COOH\), group).
(i) IUPAC name: propanoic acid.
(ii) Molecular and empirical formula: Molecular formula \(= C_3H_6O_2\). The ratio \(C{:}H{:}O = 3{:}6{:}2\) has no common factor greater than 1, so the empirical formula is also \(C_3H_6O_2\).
(iii) Products of reaction with saturated \(Na_2CO_3\) solution: a carboxylic acid reacts with the carbonate to give a salt, water and carbon dioxide:
\[2CH_3CH_2COOH + Na_2CO_3 \rightarrow 2CH_3CH_2COONa + H_2O + CO_2\]
Products: sodium propanoate, water and carbon dioxide (the effervescence of \(CO_2\) confirms the \(-COOH\) group).
(iv) Boiling point compared with the corresponding alkane: The corresponding alkane (same carbon skeleton) is butane. Propanoic acid has a higher boiling point. This is because carboxylic acid molecules form strong intermolecular hydrogen bonds (they even pair up as dimers), whereas butane molecules are held only by weak van der Waals (dispersion) forces; more energy is needed to separate the acid molecules.
(d) Manufacture from vegetable oil X (production of margarine):
- Identity of Y: hydrogen (\(H_2\)); the process is hydrogenation of the unsaturated oil.
- Function of the activated charcoal: it acts as an adsorbent that purifies/decolourises (bleaches) the oil by adsorbing coloured impurities and odours.
- Catalyst used: finely divided nickel (Ni).
- Heating X with concentrated \(NaOH\) (saponification): the oil (an ester/triglyceride) is hydrolysed to give soap (the sodium salts of the fatty acids) and glycerol (propane-1,2,3-triol).
(a)(i) Three characteristics of a homologous series.
- All members are represented by the same general formula (e.g. alkanes \(C_nH_{2n+2}\)).
- Successive members differ from the next by a \(-CH_2-\) unit (a relative molecular mass difference of 14).
- Members have similar chemical properties because they contain the same functional group.
- There is a gradual change in physical properties (e.g. boiling point rises steadily) as molar mass increases.
(Any three of the above.)
(a)(ii) Second member of the alkyne series.
Name: propyne. Structural formula: \(CH_3-C{\equiv}CH\).
(a)(iii) Combustion of ethane in excess oxygen.
\[2C_2H_{6(g)} + 7O_{2(g)} \rightarrow 4CO_{2(g)} + 6H_2O_{(l)}\]
(b) Type of reaction in the conversion of ethanol to:
- ethene: dehydration (an elimination reaction);
- ethyl ethanoate: esterification (a condensation reaction);
- chloroethane: substitution (halogenation, e.g. with \(PCl_5\) or conc. \(HCl\));
- ethoxide: redox / displacement (sodium displaces hydrogen: \(2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2\));
- ethanoic acid: oxidation.
(c) The compound shown is \(CH_3-CH_2-COOH\) (an ethyl group joined to a carboxyl, \(-COOH\), group).
(i) IUPAC name: propanoic acid.
(ii) Molecular and empirical formula: Molecular formula \(= C_3H_6O_2\). The ratio \(C{:}H{:}O = 3{:}6{:}2\) has no common factor greater than 1, so the empirical formula is also \(C_3H_6O_2\).
(iii) Products of reaction with saturated \(Na_2CO_3\) solution: a carboxylic acid reacts with the carbonate to give a salt, water and carbon dioxide:
\[2CH_3CH_2COOH + Na_2CO_3 \rightarrow 2CH_3CH_2COONa + H_2O + CO_2\]
Products: sodium propanoate, water and carbon dioxide (the effervescence of \(CO_2\) confirms the \(-COOH\) group).
(iv) Boiling point compared with the corresponding alkane: The corresponding alkane (same carbon skeleton) is butane. Propanoic acid has a higher boiling point. This is because carboxylic acid molecules form strong intermolecular hydrogen bonds (they even pair up as dimers), whereas butane molecules are held only by weak van der Waals (dispersion) forces; more energy is needed to separate the acid molecules.
(d) Manufacture from vegetable oil X (production of margarine):
- Identity of Y: hydrogen (\(H_2\)); the process is hydrogenation of the unsaturated oil.
- Function of the activated charcoal: it acts as an adsorbent that purifies/decolourises (bleaches) the oil by adsorbing coloured impurities and odours.
- Catalyst used: finely divided nickel (Ni).
- Heating X with concentrated \(NaOH\) (saponification): the oil (an ester/triglyceride) is hydrolysed to give soap (the sodium salts of the fatty acids) and glycerol (propane-1,2,3-triol).
