Chemistry 9701/22 October/November 2021: question paper and mark scheme

Question

Hydrogen iodide, HI, is a colourless gas at room temperature. (a) (i) Explain why HI has a higher boiling point than HCl and HBr. . …… . …… . …… . …… [2] (ii) The bar chart shows the boiling points of HCl, HBr and HI. The boiling point of HF is not shown. 300 280 260 boiling 240 point / K 220 200 180 160 HF HCl HBr HI Hydrogen bonds form between HF molecules. Draw a bar on the bar chart to predict the boiling point of HF. Explain your answer. . …… . …… [2] (b) The standard enthalpy change of formation, , of HI(g) is +26.5 kJ mol–1. Define the term standard enthalpy change of formation. . …… . …… . …… [2] (c) HI(g) can be formed by reacting H2(g) with I2(g). The reaction is reversible, and an equilibrium forms quickly at high temperatures. H2(g) + I2(g) 2HI(g) (i) Construct an expression for the equilibrium constant, Kp, for the reaction of H2(g) and I2(g) to form HI(g). Kp = [1] (ii) The equilibrium partial pressures of the gases at 200 °C are as follows. pH2(g) = 895 Pa pI2(g) = 895 Pa pHI(g) = 4800 Pa Calculate Kp for this reaction. Kp = …… [1] (iii) State how the value of Kp would change, if at all, if the reaction were carried out at 100 °C rather than 200 °C. Explain your answer. . …… . …… . …… . …… [2] (d) HI reacts with oxygen to form iodine and water. (i) Construct an equation for the reaction of HI with oxygen. . …… [1] (ii) Explain, with reference to oxidation numbers, why this reaction is a redox reaction. . …… . …… . …… . …… [2] (e) HI(g) can also be formed by the reaction of I2(g) with hydrazine, N2H4(g). 2I2(g) + N2H4(g) → 4HI(g) + N2(g) State the change in pressure that would occur when 2 mol I2(g) fully reacts with 1 mol N2H4(g) in a sealed container at constant temperature. Explain your answer. . …… . …… . …… . …… [2] (f) In the laboratory, HI(aq) can be formed in a two-step process. step 1 3I2(s) + 2P(s) → 2PI3(s) step 2 PI3(s) + 3H2O(l) → H3PO3(aq) + 3HI(aq) (i) Draw a ‘dot-and-cross’ diagram of a PI3 molecule. [2] (ii) Name the type of reaction in step 2. . …… [1] (iii) H3PO3(aq) and HI(aq) are both strong Brønsted–Lowry acids. Give the meaning of the term strong Brønsted–Lowry acid. . …… . …… . …… [2] (iv) Give the formula of the conjugate base of H3PO3. . …… [1] (g) HI(g) reacts with propene, CH3CH=CH2(g) to form a mixture of 1-iodopropane and 2-iodopropane. (i) Identify which of 1-iodopropane and 2-iodopropane is the major product of this reaction. Explain your answer. . …… . …… . …… . …… [2] (ii) Complete the diagram to show the mechanism of the reaction between HI and CH3CH=CH2 that forms the major product identified in (g)(i). Include curly arrows, lone pairs of electrons and charges as necessary. H 3C H C C H H H I + – [3] [Total: 26]

Question

(a) Table 1 gives physical data for some of the Period 3 elements. Table 1 atomic number, Z 11 12 13 14 15 16 17 bonding present in element M C first ionisation energy / kJ mol–1 494 736 577 786 1060 1000 1260 maximum oxidation number +7 anionic radius / nm – – – 0.271 0.212 0.184 0.181 (i) Complete the row in the table labelled ‘bonding present in element’. Use C = covalent, I = ionic, M = metallic, as appropriate. [1] (ii) Explain the difference between the first ionisation energies of the elements with atomic numbers 11 and 17. . …… . …… . …… . …… . …… [2] (iii) Explain the difference between the first ionisation energies of the elements with atomic numbers 15 and 16. . …… . …… . …… . …… . …… [2] (iv) Complete the row in the table labelled ‘maximum oxidation number’. [1] (v) Explain the variation in anionic radius for the elements with atomic numbers 14 to 17. . …… . …… . …… . …… [2] (b) Use the axes to sketch a graph that shows the trend in melting points of the elements with atomic numbers 11 to 17. melting point of element 11 12 13 14 15 16 17 atomic number, Z [2] (c) Dmitri Mendeleev published the first Periodic Table in 1869. Mendeleev used his knowledge of chemical periodicity to propose the properties of gallium, 31Ga, a Group 13 element. Table 2 gives some chemical and physical data of elements in Group 13. Table 2 density boiling point cationic radius element / g cm–3 /K / nm 5 B 2.34 3930 0.020 13 Al 2470 0.050 31 Ga 5.91 2400 49 In 7.30 0.081 81 Tl 11.8 1460 0.095 Complete the table by predicting values for the missing data. [3] (d) Indium and aluminium are elements in Group 13 of the Periodic Table. Indium has very similar chemical properties to aluminium. ● Indium reacts vigorously with hydrochloric acid to form a colourless gas and a salt in solution. ● I ndium oxide, In2O3, is amphoteric. ● Gaseous indium bromide has the formula In2Br6. This molecule contains coordinate bonds. (i) Identify the formula of the salt formed when indium reacts with hydrochloric acid. . …… [1] (ii) Construct an equation for the reaction of In2O3 with excess aqueous NaOH. . …… [1] (iii) Draw a diagram that clearly shows the types of bond present in In2Br6(g). [2] [Total: 17]

Question

Compound T is an isomer of C6H12. T (a) Name T. . …… [1] (b) Draw the skeletal formula of a structural isomer of T that shows cis-trans (geometrical) isomerism. [1] (c) Each carbon atom in T forms a sigma (σ) bond to at least one other carbon atom, as shown. H 3C CH3 C C H3C CH3 (i) On the diagram, draw the orbitals that represent the pi (π) bond that is also present in T. [1] (ii) State the hybridisation of the two carbon atoms between which the pi (π) bond forms. . …… [1] (d) A reaction scheme starting with T is shown. Reaction 2 occurs in the presence of a catalyst; knowledge of the mechanism for this reaction is not required. T U V reaction 1 HO OH reaction 2 O catalyst (i) Give the reagent(s) and conditions for reaction 1. . …… [1] (ii) State and explain how 2,4-dinitrophenylhydrazine (2,4-DNPH) can be used to detect the presence of V as a product of reaction 2. . …… . …… . …… [2] (iii) The progress of reaction 2 can be monitored by infrared spectroscopy. The absorption caused by O–H bonds is always present because water is used as a solvent. Identify two absorptions, and the bonds responsible for these absorptions, whose appearance will change significantly during the reaction. 1 . …… . …… 2 . …… . …… [2] (e) V is used in a wide range of organic reactions. Some reactions of V are shown. V W reaction 3 O O alkaline aqueous I2 O– reaction 4 NaBH4 X Y reaction 5 reaction 6 OH Z dehydration addition polymerisation (i) V and W are colourless and soluble in water. State what you would observe in reaction 3. . …… [1] (ii) Reaction 3 is a redox reaction. Identify which of the reactants is reduced in this reaction. . …… [1] (iii) Construct an equation for reaction 4. Use [H] in the equation to represent an atom of hydrogen from NaBH4. (iv) X is a mixture of two optical isomers. Draw the two optical isomers in the boxes provided. [2] (v) Both optical isomers of X can be dehydrated to form a single product, Y. Give the reagent(s) and conditions required for reaction 5. . …… [1] (vi) Y can form an addition polymer Z. Draw one repeat unit of Z. [1] (vii) Reaction 6 does not proceed quickly at room temperature. Suggest why this is the case. . …… . …… [1] [Total: 17]