2009 JC1 H1 chem Promo QP

1 2009Section A 1 (a) [5] (b) (i) (ii) [5] (c) (i) [5] (ii) (d) [2] (e) (i) (ii) [3] [20 marks] Answer the following question on writing paper. One of the most common uses of alkanes is to burn them in air in the internal combustion engine. Alkanes containing between 8 and 12 carbon atoms per molecule are preferred for this. Draw possible structural formulae for the hydrocarbon with lecular formula C8H18. Include in your answers the structure with the highest boiling point, and the structure with the lowest boiling point. Give reasons for your choice of structures. Write a balanced equation for the complete combustion octane, C8H18, and hence calculate the volume of air (at room temperature and pressure) needed to burn 57g octane. [Assume air contains 20% oxygen by vo ume.] In a separate experiment, a mixture of octane and brom was exposed to UV light. State and explain what you would observe. Ethane, C2H6, is another member of the alkane series. Explain how the boiling points of the following compounds will compare with that of ethane. chloroethane, C2H5Cl any isomer of C8H18. Ethanol, C2H5OH, is a colourless water-soluble alcohol. Draw a diagram to illustrate clearly the interaction between C2H5OH and H2O molecules. The ethene molecule, C2H4, is said to be planar. The two carbon atoms of ethene can be described as bei g joined by a and a . Briefly explain the terms in , using diagrams where appropriate. Give the numbers of and bonds present in the ethene molecule. three s p -bond -bond italics σ π

2 Section B all 2 (a) (i) (ii) (iii) [6] (b) Answer the questions in this section in the spaces provided. Beryllium chloride, BeCl2, is a molecular solid with a melting point of 399oC. When the solid is vapourised, the vapour is found to consist of a mix of gaseous molecules of BeCl2 and Be2Cl4. Draw a dot-and-cross diagram to show the electronic structure of a molecule of BeCl2. Suggest how you would expect Be2Cl4 to form from BeCl2. Draw a diagram to show the types of bonds present in the Be2Cl4 molecule. Give a value for each of the Cl-Be-Cl and Be-Cl-Be bond angles. Cl-Be-Cl = Be-Cl-Be = Ions of BeCl2 and Be2Cl4 can be obtained by passing the vapour through a plasma torch. The following equations show some of the ions formed. BeCl2 BeCl2 + + e Be2Cl4 Be2Cl4 + + e ∠ ∠ à à

3 3o Figure 1 below shows the pathway of Be2Cl4 + in an electric field. Suggest why energy is required to convert the Be2Cl4 molecule to its corresponding Be2Cl4 + ion. Indicate the polarity (+ or -) of both plates in Figure 1. In Figure1, draw and label the pathway of the BeCl2 + ion. Explain the position of this pathway. Explain the terms , and . Be2Cl4 + source Figure 1 (i) (ii) (iii) [4] [10 marks] 3 (a) [3] rate equation order of reaction rate constant

4 I II (b) Experiment number Initial conc of ester / mol dm–3 Initial conc of Br2 / mol dm–3 Initial rate of reaction / mol dm–3 s–1 (i) (ii) (iii) (iv) both (v) [9] In an experiment, bromine reacts with an ester slowly enough for the reaction to be followed by usual laboratory techniques. The following ts were obtained at 25oC. 1 2.0 10–2 2.0 10–2 6.51 10–4 2 4.0 10–2 2.0 10–2 1.29 10–3 3 6.0 10–2 2.0 10–2 1.94 10–3 4 2.0 10–2 4.0 10–2 2.55 10–3 5 2.0 10–2 6.0 10–2 Deduce the order of reaction with respect to the ester and bromine respectively. Show clearly how you obtain your answer. ester bromine Predict the initial rate of reaction in Expt 5 and complete the box above. Write the rate equation for the reaction. By what factor will the rate increase if the concentrations of the ester and bromine are doubled? In an experiment in which bromine is used in large excess, sketch on the axes below to show how I the rate of reaction varies with [ester] II [ester] varies with time 0 [ester] 0 time rate [ester] × × × × × × × × × × × × × ×

5 (c) [2] [14 marks] 4 (a) (i) (ii) [3] (b) (i) (ii) [3] [6 marks] Explain briefly how the initial reaction rate would be expected to change by increasing the temperature. Sodium peroxide, Na2O2, is used in submarines for absorbing atmospheric carbon dioxide and regenerating oxygen. The reaction produces sodium carbonate as a by- product. Write a balanced equation for this reaction. Calculate the mass of sodium peroxide needed per day to absorb the carbon dioxide produced by a crew of six submariners, each of whom exhales 500 dm3 of CO2 per day. [All volumes are measured at room temperature and pressure.] In a laboratory experiment, 1.54 g of carbon dioxide are produced and then absorbed in 50.0 cm3 of a sodium hydroxide solution forming sodium carbonate. Write a balanced equation for this reaction. Calculate the molar concentration of the sodium carbonate in the solution.

6 Section C A B C D 1 A B C D 2 A B C D 3 A C B D 4 A C B D 5 A B C D For each question there are four possible answers, , , , and . Choose the one you consider to be correct. The value of the Avogadro Constant L is 6.0 x 1023 mol-1. The mass, in g, of one molecule of propane (RMM = 44) is therefore 44.0 x 6.0 x 1023 6.0 x 1023 44 44____ 6.0 x 1023 1_______ 44 x 6.0 x 1023 Which statement about a 24 g of Mg is always correct? It contains the same number of atoms as 71 g of chlorine gas. It contains the same number of moles as 24 dm3 of neon gas at r.t.p. It contains the same number of moles as 1/12 g of C. It is liberated by 1 mole of electrons. A sample of 2.00g of iron(III) sulphate, Fe2(SO4)3, is dissolved in water to give 100 cm3 of aqueous solution. What is the concentration of SO4 2- ions? 5.0 x 10-3 mol dm-3 5.0 x 10-2 mol dm-3 1.5 x 10-3 mol dm-3 1.5 x 10-1 mol dm-3 If 1.5 dm3 of a 2.00 mol dm-3 solution and a 2.5 dm3 of a 0.60 mol dm-3 solution of the same substance were mixed, what would the concentration of substance in the resulting solution be? 1.54 mol dm-3 0.87 mol dm-3 1.13 mol dm-3 0.65 mol dm-3 In a titration 30 cm3 of 0.05 mol dm-3 phosphoric acid was found to react exactly with 15 cm3 of 0.20 mol dm-3 aqueous sodium hydroxide. The equation for the reaction occurring is NaOH + H3PO4 NaH2PO4 + H2O 2NaOH + H3PO4 Na2HPO4 + 2H2O 3NaOH + H3PO4 Na3PO4 + 3H2O NaOH + H3PO4 NaPO3 + 2H2O à à à à

7 6 not A B C D 7 A B C D 8 true A B C D 9 A B C D 10 A B C D 11 A B C D Which one of the following is a redox reaction? 2Al + 3Cl2 ? 2AlCl3 SnCl2 + HgCl2 ? Hg + SnCl4 2CrO4 2– + 2H+ ? Cr2O7 2– + H2O Cu2O + H2SO4 ? CuSO4 + Cu + H2O When ammonia is converted into nitric acid on a commercial scale, the following reactions can occur. In which reaction does the greatest change n oxidation number of nitrogen occur? 4NH3 + 5O2 ? 4NO + 6H2O 3NO2 + H2O ? 2HNO3 + NO 2NO + O2 ? 2NO2 4NH3 + 6NO ? 5N2 + 6H2O When dilute acid is added to an aqueous solution containing manganate ions and hydrogen peroxide, oxygen gas is evolved. 2MnO4 – + 5H2O2 + 6H+ ? 2Mn2+ + 8H2O + 5O2 Which one of the following statements about this reaction is ? Hydrogen ions act as a catalyst. Hydrogen peroxide acts as a reducing agent. Hydrogen ions are oxidised to water. The oxidation number of manganese changes by 6. A sample of 10.0 cm3 of 0.10 mol dm-3 iron(II) sulphate is titrated against 0.025 mol dm-3 potassium manganate(VII) in the presence of an excess f fluoride ions. It is found that 10.0 cm3 of the managante(VII) solution is required to reach the end-point. What is the oxidation number of the manganese at the end-point? +2 +3 +4 +5 The successive ionization energies, in kJ m