O-LevelChemistryOrganic Chemistry5070/21 · Oct/Nov 2018 · Q37 Marks

Tartaric acid and succinic acid are colourless organic acids. The structures of these acids are shown. [Figure showing structures of tartaric acid and succinic acid]

(a)Name the group which is present in tartaric acid but not in succinic acid.[1]
(b)Tartaric acid is reduced to succinic acid by acidified aqueous potassium iodide. What colour change would you observe in the reaction mixture when this reaction is carried out? from ............................................................. to .............................................................[2]
(c)Succinic acid is a weak acid. What is the meaning of the term weak acid?[1]
(d)Succinic acid is neutralised by aqueous sodium hydroxide. C2H4(COOH)2 + 2NaOH → C2H4(COONa)2 + 2H2O Calculate the minimum volume of 0.0200mol/dm³ sodium hydroxide required to neutralise 25.0 cm³ of 0.0500mol/dm³ succinic acid. Give your answer to three significant figures. volume .............................................................. cm³[3]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

[1] alcohol / hydroxyl
[2] colourless (1) to brown (1)
[1] acid which is only partially ionised (in water) to form H⁺ ions / acid which is partially dissociated (in water) to form H⁺ ions
[3] moles succinic acid = 1.25 × 10⁻³ (1) moles sodium hydroxide = 2.50 × 10⁻³ (1) 125 (cm³) (1)

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