O-LevelChemistryAcids, Bases & Salts5070/22 · May/June 2018 · Q910 Marks

Sulfamic acid has the structure shown. [Figure X.X]

(a)Write the molecular formula for sulfamic acid.[1]
(b)Sulfamic acid is a weak acid.
(b)(i)What is meant by the term acid?[1]
(b)(ii)What is the difference between a weak acid and a strong acid?[2]
(c)What mass of sulfamic acid is required to make 250 cm³ of a 0.150 mol/dm³ solution? mass ..................................................... g[3]
(d)In a titration, 0.00250 moles of NaOH is exactly neutralised by 0.150mol/dm³ sulfamic acid. One mole of sodium hydroxide reacts with one mole of sulfamic acid. Calculate the volume, in cm³, of sulfamic acid needed in this titration. volume ..................................................... cm³[1]
(e)One mole of aqueous sulfamic acid can produce one mole of hydrogen ions. Construct the equation to show the reaction between sulfamic acid and magnesium.[2]

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Mark scheme

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

[1] 9(a) SO3NH3 (1)
[1] 9(b)(i) (a substance that) donates hydrogen ions / (a substance that) produces hydrogen ions (in solution) (1)
[2] 9(b)(ii) weak acids partially ionise / weak acids do not completely dissociate / weak acids do not fully ionise (1) strong acids completely ionise / strong acids completely dissociate (1)
[3] 9(c) moles of acid = 0.25 × 0.15/0.0375 (1) Mr of acid = 97 (1) mass of acid (= moles of acid × Mr) = 3.6(4) (1)
[1] 9(d) 16.7 (cm³) (1)
[2] 9(e) Mg + 2SO3NH3 → H2 + Mg(SO3NH2)2 correct formula of Mg(SO3NH2)2 (1) balanced equation – dependent on correct formulae (1)

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