O-LevelChemistryRates of Reaction5070/22 · May/June 2021 · Q710 Marks

Sulfamic acid, NH₂SO₃H, is a white crystalline solid. It reacts with aqueous sodium nitrite to make nitrogen gas, as shown in the equation. NH₂SO₃H(s) + NaNO₂(aq) → N₂(g) + H₂O(l) + NaHSO₄(aq)

(a)An excess of sulfamic acid reacts with a 20.0cm³ sample of 0.150mol/dm³ NaNO₂(aq). Calculate the maximum volume, in dm³, of nitrogen formed, measured at room temperature and pressure. volume of nitrogen ... dm³[2]
(b)The rate of this reaction can be determined by measuring the volume of nitrogen formed every second. Draw a labelled diagram of the assembled apparatus that can be used to make, collect and measure the volume of nitrogen formed in this reaction.[2]
(c)The concentration of NaNO₂(aq) is increased. The temperature of the reaction remains constant. State and explain how the rate of reaction changes.[3]
(d)Sulfamic acid forms salts called sulfamates that contain the anion NH₂SO₃⁻. Magnesium carbonate, MgCO₃, is added to a sample of NH₂SO₃H(aq). Magnesium sulfamate, water and a gas are formed. The gas turns limewater milky. Construct the equation for this reaction.[3]

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

[1] moles of NaNO₂ = 0.00300 (1)
[1] volume = 0.072 (dm³) (1)
[1] correct method of collection including arrangement of apparatus (1)
[1] workable apparatus e.g. no gas leaks (1)
[1] increases (1)
[1] more crowded particles / more particles per unit volume / smaller space between particles (1)
[1] collision frequency increases / more collisions per second / increase rate of collisions (1)
[1] 2NH₂SO₃H + MgCO₃ → Mg(NH₂SO₃)₂ + H₂O + CO₂ (1)
[1] CO₂ as a product (1)
[1] correct formula for magnesium sulfamate (1)
[1] balanced equation (1)

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