A-LevelChemistryChemical periodicity9701/21 · May/June 2024 · Q212 Marks

Sulfur chloride, SCl2, is a liquid at room temperature. When SCl₂ is added to water, misty fumes are seen and a solution is made that turns universal indicator red.

(a)Sulfur chloride, SCl2, is a liquid at room temperature. When SCl₂ is added to water, misty fumes are seen and a solution is made that turns universal indicator red.
(a)(i)Identify the type of reaction that occurs when SCl2 is added to water.[1]
(a)(ii)Name a chloride of a different Period 3 element that is also a liquid at room temperature and produces misty fumes when added to water.[1]
(b)A molecule of SCl2 contains two S–Cl covalent bonds.
(b)(i)Complete the dot-and-cross diagram in Fig. 2.1 to show the arrangement of the outer electrons in a molecule of SCl2. Use x to show electrons from the chlorine atoms. Use ● to show electrons from the sulfur atom. Cl S Cl [Figure 2.1][2]
(b)(ii)Predict the shape of, and bond angle in, a molecule of SCl2 by using VSEPR theory. shape bond angle[2]
(c)Solid magnesium nitride, Mg3N2, is a crystalline solid.
(c)(i)Deduce the oxidation numbers of magnesium and nitrogen in magnesium nitride to complete Table 2.1. Table 2.1 oxidation number in Mg3N2 magnesium nitrogen[1]
(c)(ii)Magnesium nitride reacts with an excess of water to produce ammonia and magnesium hydroxide only. Construct an equation to describe this reaction.[1]
(c)(iii)Explain why the solution produced in the reaction in (c)(ii) has a pH greater than 7. Refer to the products of the reaction in your answer.[2]
(d)Boron nitride is a white solid that melts above 2900 °C. [Figure 2.2] shows part of the lattice structure of a crystal of boron nitride. boron atom nitrogen atom van der Waals' forces covalent bond
(d)(i)Use Fig. 2.2 to deduce the empirical formula of boron nitride.[1]
(d)(ii)Suggest the identity of another crystalline solid that has atoms arranged in layers similar to that of solid boron nitride.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

[1] hydrolysis
[1] silicon(IV) chloride / silicon tetrachloride
ALLOW phosphorus(III) chloride / phosphorus trichloride
[2] M1 1 shared pair of electrons between each S-Cl shown as × ●
M2 6 non-bonding electrons around each Cl shown as × AND 4 non-bonding electrons around S shown as ●
[2] M1 shape non-linear
M2 bond angle 103-105(°)
[1] Both correct for one mark
magnesium (+)II/2(+)
nitrogen -III/3-
[1] Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH3
[2] M1 due to OH-(aq)
M2 EITHER acid-base reaction of water by ammonia OR dissociation of (some) Mg(OH)2
[1] BN
[1] graphite