CJC H2 CHEM P2 Prelim

CATHOLIC JUNIOR COLLEGE Preliminary Examination 2009 Higher 2 CANDIDATE NAME CLASS CHEMISTRY 9746/02 Paper 2 Structured Questions 4 September 2009 1 hour 30 minutes Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 11 printed pages and 1 blank page. CJC Chemistry Department © CJC 2009 For Examiner’s Use 1 2 3 4 5 Total 2 T

 CJC 2009 9746/02/prelim/09 2 second ionisation energy Na Mg Al Si P S C l Ar 1 (a) The second ionisation energies of the elements in Period 3 are given in the graph below. (i) Define, by means of an equation, what is mean t by the second ionisation energy of magnesium. …………………………………………………………… …………… ……………… ...……....... (ii) Explain why the second ionisation energy of silicon is lower than that of aluminium. …………………………………………………………… …………… ……………… ...……....... …………………………………………………………… …………… ……………… ...……....... …………………………………………………………… …………… ……………… ...……....... [2] (b) Orange street lamps contain sodium metal with a sma ll amount of neon gas. The light is produced when gaseous atoms are ionised in an elect ric field. When first turned on, the lamps emit a red glow characteristic of neon but, a fter a time, the orange glow of sodium predominates. Suggest a brief explanation of this phenomenon. …..……………… …………………………………………… …………… ……………… ...……....... …..…………………………………………………………… …………… ……………… ...……....... …..…………………………………………………………… …………… ……………… ...……....... …..…………………………………………………………… …………… ……………… ...……....... [2] (c) The behaviours of the oxides and chlorides of alumi nium and silicon with water are similar, but for different reasons. Explain as fully as you can, giving balanced equa tions where relevant, why (i) aluminium oxide and silicon dioxide are both insoluble in water, and …………………………………………………… ……… …………… ……………… ...……....... …………………………………………………………… …………… ……………… ...……....... …………………………………………………………… …………… ……………… ...…….......

 CJC 2009 9746/02/prelim/09 3 (ii) aluminium chloride and silicon tetrachloride both react with water to give acidic solutions. ………………………………………………………… ……………… ……………… ...……....... …………………………………………………………… …………… ……………… ...……....... …………………………………………………………… …………… ……………… ...……....... …………………………………………………………… …………… ……………… ...……....... …………………………………………………………… …………… ……………… ...……....... [4] (d) (i) Lithium and magnesium show a diagonal relation ship, which indicates similarities in their physical and chemical properties. Predict how the solubility and basicity of lithi um oxide, Li 2O, will compare with that of barium oxide, BaO. ………………………………………………………… ……………… ……………… ...……....... …………………………………………………………… …………… ……………… ...……....... …………………………………………………………… …………… ……………… ...……....... (ii) Lithium peroxide, Li 2O2, is commonly used in spaceship cabins as an air pu rifier to absorb carbon dioxide and release oxygen: Li 2O2(s) + CO 2(g) → Li 2CO 3(s) + ½ O2(g) Calculate the percentage change in the mass of a sample of lithium peroxide when it has been fully used up. [4] [Total: 12]

 CJC 2009 9746/02/prelim/09 4 2 (a) Ammonium nitrate is commonly used in agriculture as a high-nitrogen fertiliser, and it has also been used as an oxidising agent in explosives, including improvised explosive devices. By making use of the data below, determine the en thalpy change of the following process. NH 4NO 3(l) + aq → NH 4NO 3(aq) Given: kJ mol -1 NH 4NO 3(l) → NH 3(g) + HNO 3(g) +71 ΔH (neutralization) of NH 3(aq) and HNO 3(aq) -50 ΔH (solution) of NH 3(g) -31 ΔH (solution) of HNO 3(g) +37 [3] (b) Gibbs free energy is dependent on the enthalpy and entropy changes. Comment on the following with reference to the ab ove statement: When NaHCO 3(aq) is added to HC l(aq) at room temperature, the temperature of the reaction mixture drops. Despite this, the reaction is spontaneous. …………………………………… …… ……………………… …………… ……………………....... …………………………………… …… ……………………… …………… ……………………....... …………………………………… …… ……………………… …………… ……………………....... …………………………………… …… ……………………… …………… ……………………....... …………………………………… …… ……………………… …………… ……………………....... [2] (c) The molecule of benzene is a regular hexagon in wh ich the π electrons are described as being delocalised which gives benzene its stable structure. (i) Give one chemical property which arises due to this structure. …………………………………………………… ………………………………………………

 CJC 2009 9746/02/prelim/09 5 (ii) 3-bromophenylamine, can be synthesised from benzene. Give the necessary reagents, conditions and any int ermediates formed for this synthesis. [5] [Total: 10] 3 (a) Chromium is a typical transition metal element. It forms different coloured compounds. Give the electronic configurations of Cr and Cr 3+ . Cr: …………………………………………………… ……………………..……… ……….………… Cr 3+ : ………………………………………… ………………….…… ……… ……………………. [2] (b) When aqueous ammonium dichromate(VI), (NH 4)2Cr 2O7, is added gradually to molten ammonium thiocyanate, NH 4SCN, an ammonium salt known as Reinecke’s salt, A, is formed. A has the formula NH 4[Cr(SCN) x(NH 3)y], and analysis produced the following composition by mass: Cr, 15.5 %; S, 38.1 %; N, 29.2 % (i) Calculate the values of x and y in the above formula. x : …… …………..……… ……..…………… y : …… ……………..…………………….. (ii) State the oxidation state of chromium in the c omplex, A. ………………………… …………….…………… ……………………………………………….. (iii) Draw the structure of the complex anion, showing clearly its shape. [7] NH 2 Br

 CJC 2009 9746/02/prelim/09 6 (c) Potassium dichromate(VI) undergoes the following reactions. (i) Write the equation for the reaction involved in Step I . .…..…………………………………………………………………………………… …...……… (ii) Is the reaction in Step I a redox one? Give your reasoning. .…..…………………………………………………………………………………… …...……… .…..…………………………………………………………………………………… …...……… .…..…………………………………………………………………………………… …...……… (iii) Using relevant E o data for the reaction in Step I , suggest what you might have expected the products to be instead of KCrO 3Br. (iv) Suggest a reason why the reaction does not go in the way E o data indicate. ………..……… ……………………………………………………………………………………. ………..……… ……………………………………………………………………………………. (v) Identify compound C. C: ………..……… ………………………………………………………………………………. (vi) Explain the type of reaction that occurred in Step III . ………..……… ……………………………………………………………………………………. ………..……… ……………………………………………………………………………………. ………..……… ……………………………………………………………………………………. [7] [Total: 16] K2Cr 2O7(aq) Step I 6 mol dm -3 HBr, cooled KCrO 3Br(s) orange crystals Step II 1) H 2 O 2) AgNO 3 (aq) orange solution, B cream precipitate, C Step III SO 2 (g) deep green solution, D

 CJC 2009 9746/02/prelim/09 7 4 (a) One common iron ore is magnetite, Fe 3O4. It can be obtained by heating iron with steam.