O-LevelChemistryOrganic Chemistry5070/21 · Oct/Nov 2020 · Q610 Marks

The table shows some properties of five alcohols. alcohol | formula | density in g/cm³ | boiling point in °C ---|---|---|--- methanol | CH₃OH | 0.791 | 65 ethanol | C₂H₅OH | 0.789 | 79 propanol | C₃H₇OH | 0.803 | 97 butanol | C₄H₉OH | 0.810 | 117 pentanol | C₅H₁₁OH | 0.814 | 138

(a)(i)What is the general trend in the density of the alcohols as the number of carbon atoms in a molecule increases?[1]
(a)(ii)Describe and explain the change in the boiling point of the alcohols as the number of carbon atoms in a molecule increases.[1]
(b)(i)Ethanol, C₂H₅OH, reacts with butanoic acid, C₃H₇CO₂H, to produce an ester. A few drops of a strong acid are added to catalyse the reaction. What does the term strong mean, when applied to acids?[1]
(b)(ii)Name and draw the structure of the ester produced when ethanol reacts with butanoic acid, showing all of the atoms and all of the bonds. name structure[2]
(c)Ethanol can be oxidised to ethanoic acid in the laboratory. State the reagents and conditions used in this reaction. reagent conditions[2]
(d)(i)Concentrated ethanoic acid, CH₃CO₂H, reacts with calcium. The products are calcium ethanoate and hydrogen. Construct the equation for this reaction.[1]
(d)(ii)State and explain how the rate of this reaction changes when the experiment is repeated using dilute ethanoic acid. All other conditions stay the same. Include in your answer ideas about collisions between particles.[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

[1] 6(a)(i) (density) increases
[1] 6(a)(ii) (boiling points) increase because forces of attraction between molecules are stronger / (boiling points) increase because the intermolecular forces increase
[1] 6(b)(i) (acid which is) completely ionised (in water) / (acid which is) completely dissociated (in water)
[2] 6(b)(ii) ethyl butanoate (1) H H H O H H H-C-C—C—C—O—C—C-H H H H H H (1)
[2] 6(c) (acidified) potassium manganate(VII) (1) reflux/heat (1)
[1] 6(d)(i) 2CH3CO2H + Ca → (CH3CO2)2Ca + H2
[2] 6(d)(ii) rate decreases because: fewer particles in a given volume / particles further apart / fewer particles per unit volume (1) fewer frequent collisions / particles collide less often / collision rate increases (1)

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