Chemistry 9701/21 May/June 2020: question paper and mark scheme

Question

Gallium is a metal in Group 13 of the Periodic Table. (a) There are two stable isotopes of gallium, 69Ga and 71Ga. (i) State, with reference to subatomic particles, how the isotopes 69Ga and 71Ga differ from each other. . …… . …… [1] (ii) State what further information is needed to calculate the relative atomic mass of gallium. . …… [1] (b) Gallium and its compounds show similar properties to aluminium and its compounds. Gallium reacts with excess chlorine to form gallium trichloride. (i) At 500 °C, gallium trichloride is a gas. Suggest the type of attraction that exists at 500 °C ●● between atoms within a gallium trichloride molecule . …… ●● between gallium trichloride molecules. . …… [2] (ii) When gallium trichloride is cooled a solid, Ga2Cl 6, forms. Suggest the name of the attraction formed between two gallium trichloride molecules to form Ga2Cl 6. . …… [1] (c) Gallium metal reacts rapidly when exposed to air. A white solid layer is formed on its surface. (i) Suggest an equation to describe the reaction occurring when gallium metal is exposed to air. . …… [2] (ii) The table gives the formula of each gallium-containing product formed when gallium oxide reacts separately with hot aqueous hydrochloric acid and hot aqueous sodium hydroxide. formula of gallium-containing product hot aqueous hydrochloric acid GaCl 3 hot aqueous sodium hydroxide NaGa(OH)4 Give the name of the type of behaviour shown by gallium oxide in these reactions. . …… [1] [Total: 8]

Question

(a) The equation shown in (a)(i) describes the reaction which occurs when aqueous potassium iodide is added to aqueous copper(II) sulfate. A white precipitate of copper(I) iodide forms in a brown solution of iodine and potassium sulfate. (i) Balance the equation and include state symbols. ……CuSO4(……) + ……KI(……) → ……CuI(……) + ……I2(……) + ……K2SO4(……) [2] The table gives the oxidation numbers of iodine in the different species in the equation. iodine-containing species oxidation number of iodine KI –1 CuI –1 I2 0 (ii) Deduce the oxidation number of copper in CuSO4 and CuI. ●● oxidation number of copper in CuSO4 …… ●● oxidation number of copper in CuI …… [1] (iii) Describe the type of reaction shown by the equation in (a)(i). Explain your answer in terms of electron transfer. . …… . …… . …… [2] (b) In the reaction described in (a)(i), a student uses 17.43 g of CuSO4•yH2O. By further titration of the reaction products the student concludes that the total amount of CuSO4 in the sample is 0.0982 mol. Use the Data Booklet to complete the table to calculate the value of y, where y is an integer. Show your working. mass of 0.0982 mol CuSO4 …… g amount of H2O in 17.43 g of CuSO4•yH2O …… mol H2O value of y y = …… [4] [Total: 9]

Question

Nitric acid, HNO3, can be made by reacting nitrogen dioxide with water. The enthalpy change for the reaction can be measured indirectly using a Hess’ cycle. ∆Hr 3NO2(g) + H2O(l) 2HNO3(l) + NO(g) (a) Explain what is meant by the term enthalpy change of formation. . …… . …… . …… [2] (b) Complete the Hess’ cycle using the values given in the table and hence calculate the enthalpy change, ∆Hr, for this reaction. Show your working. substance ∆Hf / kJ mol–1 NO2(g) 34.0 H2O(l) –286 HNO3(l) –173 NO(g) 91.1 ∆Hr 3NO2(g) + H2O(l) 2HNO3(l) + NO(g) ∆Hr = …… kJ mol–1 [3] (c) Nitrogen and oxygen do not react at normal atmospheric temperatures. Explain why. . …… . …… . …… . …… [2] Nitrogen oxides can be formed naturally in the Earth’s atmosphere from nitrogen and oxygen in the air. (d) State one way that nitrogen oxides are produced naturally. . …… [1] (e) Nitrogen dioxide, NO2, acts as a homogeneous catalyst in the oxidation of atmospheric sulfur dioxide. (i) Explain why NO2 is described as a homogeneous catalyst. . …… . …… . …… . …… [3] (ii) Write equations which describe the two reactions occurring when NO2 acts as a catalyst in the formation of sulfur trioxide from sulfur dioxide. . …… . …… [2] [Total: 13]

Question

Calcium nitrate, Ca(NO3)2, reacts with ammonia, carbon dioxide and water to form a mixture of ammonium nitrate and calcium carbonate. Ca(NO3)2 + 2NH3 + CO2 + H2O → 2NH4NO3 + CaCO3 (a) Explain why ammonia is described as a Brønsted‑Lowry base in this reaction. . …… [1] The product mixture can then be added to soil. (b) State two reasons why this mixture of products is added to some soils. 1 . …… 2 . …… [2] (c) Complete the table to name the shape and give the bond angle of each species. name of shape bond angle / ° CO2 NH3 H 2O [3] [Total: 6]

Question

(a) Below is a list of species which can react with organic compounds. CN– HCl Cl H2O CO32– (i) From the list, identify a species which can react with ethane. . …… [1] (ii) From the list, identify two species which can attack the π bond in ethene. . …… [1] (iii) From the list, identify a species which can be used to distinguish between solutions of propanoic acid and propan-1-ol. Describe any relevant observations. . …… . …… . …… [2] (b) Cl (g) can be made from Cl 2(g). (i) Describe the conditions required for this process. . …… [1] (ii) Name this process. . …… [1] (c) (i) Name an organic functional group which reacts with a nucleophile in an addition reaction. . …… [1] (ii) Name an organic functional group which tends to react with a nucleophile in an SN1 substitution mechanism. . …… [1] (d) But-1-ene reacts with steam in the presence of concentrated phosphoric acid to form two isomers of molecular formula C4H10O. Each reaction occurs via a different intermediate ion. (i) Draw the structure of both intermediate ions. [2] (ii) Circle the more stable intermediate ion drawn in (d)(i). Explain your answer. . …… . …… . …… [2] [Total: 12]

Question

2-methylbut-1-ene reacts with acidified manganate(VII) ions, under specific conditions, to produce two organic compounds X and Y. X immediately reacts with the acidified manganate(VII) ions to form carbon dioxide and water. Y has the structural formula CH3CH2COCH3. acidified manganate(VII) ions X Y 2-methylbut-1-ene + CH3CH2COCH3 CO2 + H2O (a) Draw the skeletal formula of 2-methylbut-1-ene. [1] (b) (i) State the specific conditions required for the acidified manganate(VII) ions to react with 2-methylbut-1-ene in this way. . …… [1] (ii) Name the type of reaction occurring to the functional group in 2‑methylbut‑1‑ene in the reaction in (b)(i). . …… [1] (c) Draw the structural formula of X. . …… [1] (d) Describe a chemical test and the expected observation(s) to confirm the presence of the carbonyl functional group in Y. . …… . …… [2] (e) The infra-red spectrum of 2-methylbut-1-ene is shown. 1 0.8 0.6 relative transmittance 0.4 0.2 4000 3000 2000 1000 wavenumber / cm–1 Predict two main differences that would be seen between the spectra of Y, CH3CH2COCH3, and of 2-methylbut-1-ene. Give reasons for your predictions. Your answer should refer only to the region of each spectrum above 1500 cm–1. . …… . …… . …… . …… . …… [2] (f) Propanoic acid, CH3CH2CO2H, is reduced by LiAl H4. (i) Write an equation to show this reaction. Use [H] to represent an atom of hydrogen from the reducing agent. . …… [1] (ii) Name the organic product formed in this reaction. . …… [1] (g) Organic compound W is an ester which is a structural isomer of propanoic acid. (i) State the molecular formula of W. . …… [1] (ii) Draw a possible structure of W. [1] [Total: 12]