Questions 1
Topic – 11.1 Physical properties of the Group 17 elements
(a) The elements of Group 17 are called halogens. Complete Table 1.1.
(b) State the trend in volatility of the halogens chlorine, bromine and iodine. Explain your answer.
(c) Iodine is made by reacting bromine with sodium iodide.
(i) Construct an ionic equation for the reaction of bromine with sodium iodide.
(ii) State the role of bromine in the reaction. Explain your answer.
(d) Concentrated sulfuric acid is added to separate samples containing equal amounts of NaCl, NaBr and NaI. All three samples initially react to produce the hydrogen halide.
(i) Write an equation to describe the acid–base reaction that occurs when concentrated sulfuric acid reacts with NaBr.
(ii) Deduce which sodium halide, NaCl, NaBr or NaI, produces the largest percentage yield of hydrogen halide when concentrated sulfuric acid is added. Explain your answer by considering the relative reactivity of the halide ions as reducing agents.
identity of sodium halide …………………..
explanation …………………………….
▶️Answer/Explanation
Ans:
1(a) 
(b) M1 (it / volatility) decreases
M2 more electrons in molecules
M3 (so) increased strength of instantaneous dipole– induced dipole forces (of attraction)
(c)(i) Br₂ + 2I⁻ → 2Br⁻ + I₂
(ii) (Br₂/bromine is an) oxidising agent
AND
removes electron(s) from iodide (ions) I⁻ OR increases the oxidation number of I⁻ / iodide (ion)
(d)(i) NaBr + H₂SO₄ → HBr + NaHSO₄
OR
2NaBr + H₂SO₄ → 2HBr + Na₂SO₄
(ii) M1 sodium chloride
M2 Cl⁻ is not a strong enough reducing agent to reduce H₂SO₄
M3 Br⁻ & I⁻ are strong enough reducing agents to react (further) with (the S in) H₂SO₄
Alternative M2 and M3
M2 ability to behave as reducing agents increases down the group
M3 EITHER Cl⁻ is not strong enough to reduce H₂SO₄ OR Br⁻ and I⁻ react (further) with (the S in) H₂SO₄
Questions 2
Topic – 9.1 Periodicity of physical properties of the elements in Period 3
(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.
(i) Identify the type of reaction that occurs when SCl₂ is added to water.
(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.
(b) A molecule of SCl₂ contains two S–Cl covalent bonds.
(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 × to show electrons from the chlorine atoms.
Use ● to show electrons from the sulfur atom.
(ii) Predict the shape of, and bond angle in, a molecule of SCl₂ by using VSEPR theory.
(c) Solid magnesium nitride, Mg₃N₂, is a crystalline solid.
(i) Deduce the oxidation numbers of magnesium and nitrogen in magnesium nitride to complete Table 2.1. 
(ii) Magnesium nitride reacts with an excess of water to produce ammonia and magnesium hydroxide only. Construct an equation to describe this reaction.
(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.
(d) Boron nitride is a white solid that melts above 2900°C. Fig. 2.2 shows part of the lattice structure of a crystal of boron nitride 
(i) Use Fig. 2.2 to deduce the empirical formula of boron nitride.
(ii) Suggest the identity of another crystalline solid that has atoms arranged in layers similar to that of solid boron nitride.
▶️Answer/Explanation
Ans:
(a)(i) hydrolysis
(ii) silicon(IV) chloride / silicon tetrachloride
ALLOW phosphorus(III) chloride / phosphorus trichloride
(b)(i) 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 ●
(ii) M1 shape non-linear
M2 bond angle 103–105(°)
(c)(i)
(ii) Mg₃N₂ + 6H₂O → 3Mg(OH)₂ + 2NH₃
(iii) M1 due to \(OH^–(aq)\)
M2 EITHER acid-base reaction of water by ammonia OR dissociation of (some) Mg(OH)₂
(d)(i) BN
(ii) graphite
Questions 3
Topic – 7.1 Chemical equilibria: reversible reactions, dynamic equilibrium
(a) Define Le Chatelier’s principle.
(b) Reaction 1 describes the reversible reaction between yellow Fe³⁺(aq) and colourless SCN⁻(aq) to produce red FeSCN²⁺(aq).
reaction 1 Fe³⁺(aq) + SCN⁻(aq) \( \rightleftharpoons \)FeSCN²⁺(aq) ∆H = –x kJmol⁻¹
yellow colourless red
A mixture of Fe³⁺(aq), SCN⁻(aq), and FeSCN²⁺(aq) is at equilibrium at 20°C. The temperature of this mixture is then increased to 50°C and allowed to reach equilibrium. Deduce the changes that occur, if any, in the equilibrium mixture at 50°C compared to the equilibrium mixture at 20°C.
• change in appearance
………………………………………………………………………………………………………………………….
• change in relative concentration of FeSCN²⁺(aq)
………………………………………………………………………………………………………………………….
• change in value of the equilibrium constant, \(K_c\)
(c) In another experiment, equimolar amounts of Fe³⁺(aq) and SCN⁻(aq) are mixed together and allowed to reach equilibrium. The total volume of the mixture is 25.0 cm³.
reaction 1 Fe³⁺(aq) + SCN⁻(aq) \( \rightleftharpoons \) FeSCN²⁺(aq)
At equilibrium the mixture contains:
• [SCN⁻] = \(1.30 × 10^{–3}moldm^{–3}\).
• [FeSCN²⁺] = \(0.300 × 10^{–3}moldm^{–3}\).
(i) Calculate the initial amount, in mol, of Fe³⁺(aq) added to SCN⁻(aq) to produce this mixture.
(ii) Calculate \(K_c\) for reaction 1 and state its units. Show your working.
▶️Answer/Explanation
Ans:
(a) M1 (if a change in conditions occurs) the equilibrium shifts
M2 to minimise the change in conditions
(b) M1 change in appearance paler red / more yellow / less orange
M2 change in relative concentration of \(FeSCN^{2+}\)(aq) lower
M3 change in value of the equilibrium constant, \(K_c\) lower
(ii) M1 value for \(K_c = 178\)
M2 units = mol⁻¹ dm³
Questions 4
Topic – 5.1 Enthalpy change, ΔH
(a) Define enthalpy change of formation.
(b) Iron is made when iron(III) oxide is heated with carbon monoxide, as shown by reaction 2.
reaction 2 Fe₂O₃ + 3CO → 2 Fe + 3 CO₂
Table 4.1 shows enthalpy change of formation data measured at 298K and 101kPa.
(i) Complete Table 4.1 by adding equations with relevant state symbols to represent:
• standard enthalpy change of formation for Fe₂O₃.
• standard enthalpy change of formation for CO.
(ii) Use the data in Table 4.1 to calculate the enthalpy change of reaction, \(∆H_r\), in \(kJmol^{–1}\), for reaction 2. Show your working
▶️Answer/Explanation
Ans:
(a) M1 (enthalpy change / energy change) when one mole of a compound / substance is formed
M2 from its elements in their standard states
Questions 5
Topic – 3.4 Covalent bonding and coordinate (dative covalent) bonding
Hydrocarbon molecules contain covalent bonds.
(a) Define covalent bond.
(b) A C=C bond in an alkene is made from a σ bond and a π bond.
(i) Identify the hybridisation of the carbon atoms in a C=C bond in an alkene.
(ii) Draw labelled diagrams to show, in terms of orbital overlap, how the σ and π bonds are made in a C=C bond.
σ bond
π bond
(c) In electrophilic reactions involving alkenes the π bond of C=C is broken.
(i) Suggest one difference between σ and π bonds that explains why the π bond is broken in electrophilic addition reactions involving alkenes.
(ii) Complete Fig. 5.1 to show the mechanism for the electrophilic addition of hydrogen bromide to 2-methylpropene to produce the major organic product. Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate.
▶️Answer/Explanation
Ans:
(a) (electrostatic) attraction between nuclei of two atoms and shared pair of electrons
(b)(i) \(sp^2\)
(c)(i) EITHER (pair of) electrons in 𝜋 bond are further away from the nuclei so weaker attraction
OR (pair of) electrons in 𝜎 bond are closer to the two nuclei so stronger attraction
Questions 6
Topic – 13.4 Isomerism: structural isomerism and stereoisomerism
(a) V shows stereoisomerism.
(i) Explain what is meant by stereoisomerism.
(ii) Deduce the number of stereoisomers of V. Explain your reasoning.
(iii) Deduce the molecular formula of V.
(iv) Name all the functional groups present in V.
(b) Fig. 6.2 shows two reactions involving V.
(i) Identify the role of reagent T for each functional group that reacts in reaction 1.
(ii) Suggest the identity of reagent U in reaction 2.
(c) Both functional groups in one molecule of Y react with an inorganic reagent to form one molecule of Q and one molecule of methanol, CH₃OH, as shown in Fig. 6.3. 
(i) Part of the mass spectrum for Q is shown in Fig. 6.4. Only peaks with m/e greater than 198 are shown. 
Calculate the relative abundance, x, of the peak at m/e = 201. Show your working.
(ii) Q contains only hydroxyl functional groups. Complete Table 6.1 to show the observations that occur when 2,4-dinitrophenylhydrazine (2,4-DNPH reagent) is added to separate samples of Y and Q.
(iii) Under certain conditions, 0.0020mol of Q reacts with an excess of sodium to produce a total of 44.8 cm³ of gas at s.t.p. Calculate the number of hydroxyl groups present in a molecule of Q. Show your working.
(iv) Use Table 6.2 to describe and explain two differences between the infrared spectrum of Y and Q in the region above 1500 cm⁻¹.
▶️Answer/Explanation
Ans:
(a)(i) (molecules with the) same structural formula (and same molecular formula) with different arrangement of atoms / groups in space
(ii) M1 number of stereoisomers = 8
M2 reasoning: 2 chiral centres AND 1 C=C (producing a cis-and-trans or geometrical pair)
(iii) \(C_{13}H_{20}O_3\)
(iv) ester AND carbonyl / ketone AND C=C (bond) / alkene
(b)(i) reducing agent for C=O AND C=C
(ii) sodium borohydride / NaBH₄
(c)(i) M1 deduce n = 12 (from Y – 1C (in methanol))
M2 \((100\times x) ÷ (1.1\times 100)\) = 12 (so) x = 13.2
(iii) ROH + Na→ RONa + 1/2 H₂
(0.002 mol Q produced 0.002 mol \(H_2\) gas so) 2 OH groups
M1 answer indicates that OH group(s) in Q react with Na to produce the H₂ in the ratio 1 mol OH : ½ mol \(H_2\)
M2 uses data to show 2OH group
(iv) M1 Y will have absorption / peak / trough between 1670–1740 due to C=O (Q will not)
M2 Q will have absorption / peak / trough between 3200–3600 due to O-H (Y will not)