MI_Prelim 2008 H2 Chemistry Paper 2

Class Adm No Candidate Name: This question paper consists of 13 printed pages. [Turn over Preliminary Examinations 2008 Pre-university 3 H2 CHEMISTRY 9746 / 02 Tuesday 9 Sep 2008 1h 30 min Additional materials: Data Booklet READ THESE INSTRUCTIONS FIRST 1. Do not turn over this question paper until you are told to do so. 2. Write your name, class and index number in the spaces provided at the top of this page. 3. Write in dark blue or black pen in the spaces provided on the Question Paper. 4. You may use a soft pencil for any diagrams or graphs. 5. DO NOT use paper clips, highlighters, glue or correction fluid or tape. 6. Answer ALL the questions. 7. Give non-exact numerical answers correct to 3 significant figures , or 1 decimal place in the case of Mr and Ar, unless a different level of accuracy is specified in the question. 8. The number of marks is given in brackets [ ] at the end of each question or part question. 9. You are reminded of the need for clear presentation in your answers and to show all working in calculations. 10. The use of a calculator is expected, where appropriate. Paper 2 Question No 1 2 3 4 5 6 7 Marks Obtained 60

1. Electrical generating plants transport large amounts of hot water through copper pipes, and oxygen dissolved in the water can cause a major corrosion problem, Hydrazine (N2H4) is added to avoid the problem by reacting with the oxygen: N2H4(aq) + O2(g) → N2(g) + 2 H2O(l) (a) Draw dot-and-cross diagram for hydrazine and determine the bond angle with respect to a nitrogen atom. [2] Bond angle: ……………………… (b) Explain the data below. [3] Compound Melting point / oC N2H4 1 P2H4 -134 CH3CH2NH2 -81 ………………………………………………………………………………………………. ………………………………………………………………………………………………. ………………………………………………………………………………………………. ………………………………………………………………………………………………. ………………………………………………………………………………………………. ………………………………………………………………………………………………. ………………………………………………………………………………………………. 2

(c) With the use of the Data Booklet, draw an energy level diagram for the formation of N2H4 and determine the standard enthalpy change of formation of N2H4. [3] (d) An alternative method suggested to prevent the copper pipes from corroding is to coat the copper pipes with a layer of aluminium oxide. (i) Complete the diagram below, by filling in correct labels into the empty boxes, to illustrate the process. [1] (ii) Write the half equations for reactions which occur at the anode and cathode. [ 2 ] Cathode: ……………………………………………………………………… Anode: ……………………………………………………………………… ……………………………………………………………………… [Total: 11m] 3

2. The following reaction is sometimes used to produce H 2 needed for production of ammonia in the Haber process. CH4(g) + CO2(g) 2CO(g) + 2H2(g) Temperature / K Kp 1200