O-LevelChemistryOrganic Chemistry5070/21 · May/June 2017 · Q1010 Marks
The table shows some information about the homologous series of unbranched carboxylic acids. name | structure | boiling point/°C --- | --- | --- methanoic acid | HCO₂H | 101 ethanoic acid | CH₃CO₂H | 118 propanoic acid | CH₃CH₂CO₂H | 141 butanoic acid | CH₃CH₂CH₂CO₂H | 164 pentanoic acid | CH₃CH₂CH₂CH₂CO₂H | 186
- (a)(i)Deduce the general formula for the homologous series of unbranched carboxylic acids.[1]
- (a)(ii)Describe two other properties of a homologous series.[2]
- (b)(i)What is the meaning of the term weak acid?[1]
- (b)(ii)Aqueous propanoic acid reacts with magnesium carbonate. Construct the equation for this reaction.[1]
- (c)Butanoic acid reacts with ethanol to make an ester. Name and draw the structure of this ester. Show all of the atoms and all of the bonds within the ester linkage. name .......................................................................................... structure[2]
- (d)Ethanoic acid is a liquid at room temperature and has a boiling point of 118°C. Describe the changes in both the arrangement and movement of the molecules when ethanoic acid is heated from room temperature to 120°C.[3]
Mark scheme
Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.
- B10(a)(i) CnH2n+1COOH / CnH2nO2 (1)
- B10(a)(ii) ANY TWO FROM:
- Same functional group (1)
- Idea that each member varies by a CH2 group (1)
- Same or similar chemical properties (1)
- Physical properties change with a trend (1)
- B10(b)(i) An acid that partially ionises / partially dissociates (1)
- B10(b)(ii) MgCO3 + 2CH3CH2CO2H Mg(CH3CH2CO2)2 + CO2 + H2O (1)
- B10(c) Ethyl butanoate (1)
- O-C2H5
- C3H7-C (1)
- B10(d) (Molecules) move faster / have more kinetic energy (as temperature increases) (1)
- (Molecules) are further apart (as temperature increases) (1)
- (Molecules) are arranged more randomly / more irregularity (as temperature increases) (1)
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