Cambridge A Level Chemistry 9701 — 2025 Oct/Nov Paper 2 · Variant 4

1 The Group 17 elements are oxidising agents. (a) (i) Explain how the Group 17 elements act as oxidising agents. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Write an equation to show the reaction in which Cl oxidises aluminium metal. 2 ..................................................................................................................................... [1] (iii) A student heats equal amounts of I2(g) and H2(g) in a sealed flask. The student leaves the contents to cool. State what you would observe during the reaction. ..................................................................................................................................... [1] (b) Cl and can each react with to give and a hydrogen halide, HX. 2 Br2 NH3 N2 3X2 + 2NH3 N2 + 6HX X = Cl or Br The relative bond strengths of X–X and H–X determine the difference in enthalpy change of the two reactions. (i) Describe and explain the difference in the X–X bond strengths of Cl and 2 Br2. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (ii) Describe the relative thermal stabilities of HCl and HBr. ..................................................................................................................................... [1] (iii) Define enthalpy change of formation, ΔHf. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (iv) Table 1.1 gives data relevant to the reaction of Cl 2(g) with NH3(g). Table 1.1 enthalpy change of compound formation, ΔHf / kJ mol–1 NH3(g) – 46 HCl (g) –92 Use the data in Table 1.1 to calculate the enthalpy change of the reaction of Cl 2(g) with NH3(g). enthalpy change of reaction = ........................................... kJ mol–1 [2] (v) I2 reacts with NH3 to form NI3. Predict the shape of a molecule of NI3. Explain your answer. shape ................................................................................................................................ explanation ........................................................................................................................ ........................................................................................................................................... [2] (c) Table 1.2 shows some information about reactions of NaCl , NaBr and NaI. Table 1.2 NaCl NaBr NaI observation white precipitate with Ag+(aq) type of reaction with acid–base acid–base, then redox acid–base, then redox concentrated H2SO4 • black solid observations with • yellow solid concentrated H2SO4 • effervescence (i) Complete Table 1.2. [4] (ii) Suggest an identity for the species that produces each observation in the reaction of NaI with concentrated H2SO4. black solid ......................................................................................................................... yellow solid ........................................................................................................................ effervescence .................................................................................................................... [2] (d) Table 1.3 gives some information about MgCl and SiCl 2 4. Table 1.3 MgCl SiCl 2 4 electrical conductivity when liquid conducts does not conduct observation when added to water dissolves vigorous reaction (i) Explain the difference between the electrical conductivity of liquid MgCl and of liquid 2 SiCl 4. Refer to bonding and relevant particles in your answer. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (ii) Suggest the pH of the solutions that form when each chloride is added to water. MgCl ......................................................... SiCl ......................................................... 2 4 [2] [Total: 22]

Mark scheme: Question Answer Marks 1(a)(i) (halogens can) remove electron(s) (from a reactant) 1 1(a)(ii) 2Al + 3Cl 2 → 2Al Cl 3 1 1(a)(iii) purple (gas) disappears 1 1(b)(i) M1 Br—Br is weaker (than Cl —Cl) AND Br atoms are larger 2 M2 less (significant) overlap of orbitals (in Br-Br) 1(b)(ii) HCl is more thermally stable 1 1(b)(iii) M1 (enthalpy change / energy change) when one mole of a compound / substance is formed 2 M2 from its (constituent) elements in their standard state(s) 1(b)(iv) M1 (6 × –92) – (2 × –46) = 2 M2 –460 (kJ mol−1) 1(b)(v) M1 (trigonal) pyramidal 2 M2 three bonding pairs AND one lone pair (of electrons) 1(c)(i) 4 NaCl NaBr NaI with Ag+(aq) white precipitate M1 cream / off-white M2 yellow ppt ppt with conc. acid – base acid – base, acid – base, H2SO4 then redox then redox observations M3 steamy fumes M4 brown liquid • black solid with conc. OR OR • yellow solid H2SO4 fizzing fizzing • effervescence 1(c)(ii) M1 black solid = iodine / I2 AND yellow solid = sulfur / S(8) 2 M2 effervescence = hydrogen sulfide / H2S(g) 1(d)(i) M1 MgCl2 (is ionic and) has mobile ions 2 M2 SiCl 4 is covalent AND no charge carriers OR (no ions and) no delocalised electrons OR no mobile / moving ions 1(d)(ii) M1 MgCl 2 pH = 7 2 M2 SiCl 4 pH 0 – 4

More questions on Some reactions of the halide ions

2 Aluminium oxide, Al 2O3, and phosphorus(V) oxide, P4O10, are both used as reagents and catalysts. (a) The melting point of Al 2O3 is 2072 °C. The melting point of P4O10 is 340 °C. Explain the difference in the melting points of these two compounds. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [3] (b) A 5.00 dm3 sealed flask contains 0.400 mol of CO(g) and 0.800 mol of H2(g) and an Al 2O3 catalyst. The flask is heated to a temperature of 290 °C and allowed to reach equilibrium. Equation 1 shows the reaction. equation 1 CO(g) + 2H2(g) CH3OH(g) The equilibrium constant, Kc, of equation 1 is given. [CH3OH] Kc = [CO][H2]2 (i) State the units of Kc. ..................................................................................................................................... [1] (ii) The equilibrium mixture contains 0.280 mol of CH3OH(g). Calculate the value of Kc. Give your answer to three significant figures. value of Kc = ......................................................... [3] (iii) State and explain the effect, if any, on the value of Kc when the overall pressure in the sealed flask is increased. ........................................................................................................................................... ..................................................................................................................................... [1] (c) P4O10 catalyses the reversible reaction of CO with H2 to form CH3OH. equation 1 CO(g) + 2H2(g) CH3OH(g) P4O10 then acts as a dehydrating agent, causing CH3OH to form CH3OCH3. (i) Explain how the presence of a catalyst affects a chemical reaction. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Construct an equation for the dehydration reaction of CH3OH to form CH3OCH3. ..................................................................................................................................... [1] (iii) Write an equation to show the reaction of P4O10 with an excess of water. ..................................................................................................................................... [1] [Total: 11]

Mark scheme: 2(a) M1 Al 2O3 is ionic 3 M2 P4O10 is a (simple) molecule M3 ionic bonds are stronger than intermolecular forces 2(b)(i) mol–2 dm6 1 2(b)(ii) M1 at equilibrium: moles of CO = 0.120 AND moles of H2 = 0.240 3 M2 [CH3OH] = 0.056 AND [CO] = 0.024 AND [H2 ] = 0.048 M3 use of Kc with correct evaluation = 1.01  103 2(b)(iii) no effect AND Kc is not affected by pressure 1 2(c)(i) increases rate by providing a different mechanism with a lower activation energy 1 2(c)(ii) 2CH3OH → CH3OCH3 + H2O 1 2(c)(iii) P4O10 + 6H2O → 4H3PO4 1

More questions on Chemical equilibria: reversible reactions, dynamic equilibrium

3 Propan-2-ol, (CH3)2CHOH, is sometimes added to fuel to help it burn. Fig. 3.1 shows some reactions of propan-2-ol. propan-2-ol reaction 3 reaction 1 OH concentrated acidified K2Cr2O7 H2SO4 L K alkaline reaction 2 I2(aq) CH3CO2 – and CHI3 Fig. 3.1 (a) (i) Draw the structure of organic compound K. [1] (ii) State an observation you would make in reaction 2. ..................................................................................................................................... [1] (iii) State the type of reaction that is shown in reaction 3. ..................................................................................................................................... [1] (iv) Complete Fig. 3.2 to show the pi (π) bond in L that is formed from orbital overlap. H H C C H3C H Fig. 3.2 [1] (b) Propan-2-ol reacts with sodium to produce (CH3)2CH–O – anions. These anions react with 2-bromopropane to form compound N, as shown in Fig. 3.3. N Br (CH3)2CH–O– O Fig. 3.3 (i) Write an equation for the reaction of propan-2-ol with sodium. ..................................................................................................................................... [1] (ii) The reaction of 2-bromopropane with (CH3)2CH–O – anions follows an SN1 mechanism. Complete Fig. 3.4 to show this mechanism. Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate. H H H H3C C Br H3C C O C CH3 CH3 CH3 CH3 (CH3)2CH–O– Fig. 3.4 [3] (iii) Suggest how the rate of the SN1 reaction would change, if at all, if 2-chloropropane were used instead of 2-bromopropane. Explain your answer. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (iv) N is also added to petrol to make it burn more smoothly. Construct an equation for the complete combustion of N, C6H14O. C6H14O ........................................................................................................................ [1] [Total: 11]

Mark scheme: 3(a)(i) 1 3(a)(ii) yellow precipitate 1 3(a)(iii) elimination 1 3(a)(iv) 1 3(b)(i) 1 1 (CH3)2CHOH + Na → (CH3)2CHO(–)Na(+) + H2 2 3(b)(ii) M1 correct dipole on δ+C—Brδ– AND curly arrow from C—Br bond to Br 3 M2 intermediate M3 curly arrow from lone pair of (CH3)2CHO– to C+ 3(b)(iii) M1 rate would decrease 2 M2 C—Br is weaker (than C—Cl, so breaks more easily) 3(b)(iv) C6H14O + 9O2 → 6CO2 + 7H2O 1

More questions on Alcohols

4 Compounds P and Q are structural isomers. P Q Fig. 4.1 (a) (i) Define structural isomerism. ........................................................................................................................................... ..................................................................................................................................... [2] (ii) P shows geometrical isomerism. Draw the geometrical isomer of P. Explain why the two isomers are not identical. geometrical isomer of P explanation ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] (iii) Both P and Q react with aqueous bromine. Name the mechanism of this reaction. ..................................................................................................................................... [1] (iv) Q is oxidised by hot concentrated acidified KMnO4(aq), forming two different organic products. Construct an equation for this reaction. Use [O] to represent an atom of oxygen from the oxidising agent. (CH3)2C=CHCH3 ......................................................................................................... [2] (v) Q reacts with HBr(g) to produce two structural isomers, R and S, as shown in Fig. 4.2. Q R S HBr(g) and Br Br Fig. 4.2 State and explain why isomer S is the major product of the reaction. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (vi) The mass spectrum of R shows peaks at m / e = 150 and m / e = 152. Suggest structures for the ions responsible for these peaks. peak at m / e = 150 peak at m / e = 152 [2] (b) Fig. 4.3 shows a synthesis starting from T, a different isomer of R and S. T U V reaction 1 reaction 2 HCl (aq) Br CN COOH Fig. 4.3 (i) Identify the reagent and conditions for reaction 1. ..................................................................................................................................... [1] (ii) Reaction 2 is a hydrolysis reaction. Construct an equation for reaction 2. (C2H5)2CHCN .............................................................................................................. [1] (iii) V reacts with propan-2-ol in the presence of a catalytic amount of H2SO4 to form organic compound W. Complete Table 4.1 to give details of this reaction. Table 4.1 reaction of V with propan-2-ol type of reaction functional group formed molecular formula of organic product W [3] [Total: 16]

Mark scheme: 4(a)(i) M1 (molecules with the) same molecular formula / same number of atoms of each element 2 M2 different structural formulae/structures 4(a)(ii) 2 M1 M2 restricted / lack of / no rotation about C=C 4(a)(iii) electrophilic addition 1 4(a)(iv) M1 CH3COCH3 + CH3COOH as products 2 M2 (CH3)2C = CHCH3 + 3[O] → CH3COCH3 + CH3COOH 4(a)(v) M1 (reaction proceeds via a) more stable intermediate / carbocation 2 M2 because of greater positive inductive effect of more alkyl groups 4(a)(vi) 2 M1 M2 4(b)(i) KCN in ethanol (and heat) 1 4(b)(ii) (C2H5)2CHCN + 2H2O + HCl → (C2H5)2CHCOOH + NH4Cl 1 4(b)(iii) 3 reaction of V with propan-2-ol type of reaction M1 condensation functional group formed M2 ester molecular formula of M3 C9H18O2 organic product W

More questions on Isomerism: structural isomerism and stereoisomerism