ACJC Chemistry Complete P 2 Prelims

Centre Number Index Number Name and Class ANGLO-CHINESE JUNIOR COLLEGE PRELIMINARY EXAMINATIONS Advanced Level CHEMISTRY 9746/02 Higher 2 Paper 2 Structured 22 August 2008 1 hour 30 minutes Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, Centre number and index number on all the work you hand in. Write in dark blue or black pen. 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. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together including the cover page. For Examiner's Use Question no. Marks 1 2 3 4 5 TOTAL This document consists of 12 printed pages. 1

1 (a) On heating, Group I metal nitrates such as sodium nitrate(V) decompose giving the metal nitrate(III) and oxygen, while Group II metal nitrates, for example magnesium nitrate(V), decompose giving different products. (i) Write balanced equations for the decomposition of sodium nitrate(V) and magnesium nitrate(V) respectively. [2] 15.35 g of a mixture of sodium nitrate(V) and magnesium nitrate(V) was heated in a fume cupboard until no more gases were evolved. The water soluble part of the residue was dissolved in water to prepare 1.00 dm 3 of solution. 10.00 cm 3 of this solution was reacted with 20.00 cm3 (in excess) of 0.0200 mol dm-3 potassium manganate(VII) solution, acidified with dilute sulphuric acid. (ii) The nitrate(III) half equation is NO 2 - + H2O NO3 - + 2H+ + 2e- Write a balanced equation for the reaction between nitrate(III) ions and manganate(VII) ions. [1] The excess potassium manganate(VII) required 12.00 cm 3 of 0.0500 mol dm-3 ethanedioic acid solution for complete reaction. [ 2MnO 4 - + 5C2O4 2- + 16H+ 2Mn2+ + 10CO2 + 8H2O ] (iii) Calculate the amount in moles of the nitrate(III) ions in the 10.00 cm3 solution. [2] 2

(iv) Hence, calculate the mass of each nitrate in the mixture. [2] (b) Magnesium nitrate(V) and strontium nitrate(V) decompose similarly on heating. However, magnesium nitrate(V) decomposes at a lower temperature than strontium nitrate(V). Explain why these two nitrates decompose at different temperatures. [2] (c) Ammonium nitrate(V) decompose to produce nitrous oxide, N 2O. Nitrous oxide is relatively inert at room temperature but at 500oC, it decomposes to oxygen, nitrogen and nitric oxide, NO. In the spaces provided, draw the dot and cross diagrams of these two oxides of nitrogen. [2] [Total: 11] Formula Nitrogen oxidation state Dot and Cross Diagram N2O +1 NO +2 3

2 (a) The first ionisation energies of nine elements from sodium to potassium are shown in the sketch below. Give reasons for: (i) the general trend across the period from Na to Ar. [2] (ii) the discontinuity between Mg and Al. [1] (iii) the discontinuity between P and S. [1] 11 12 13 14 15 16 17 18 19 number of protons First IE / kJ mol- • 1 •• ••• •• •Na Mg Al Si P S Cl Ar K 4

(iv) the difference between the first ionisation energies of Na and K. [1] (b) (i) Sketch the melting point trend of elements in period 3. [1] (ii) Explain the difference in melting points for sodium and silicon in terms of their structures and bonding. [3] 5

(c) Sodium was first produced commercially in 1855 by thermal reduction of sodium carbonate with carbon in what is known as the Deville process. Na2CO3(l) + 2C(s) → 2Na(g) + 3CO(g) The standard entropy change of reaction, ∆Sr θ is +549 J K-1 mol-1 (i) Explain why the entropy change of the above reaction is positive. [1] (ii) Determine the range of temperatures for the above reaction to be feasible. Na 2CO3(l) CO(g) Na(g) ΔHf Ө / kJ mol-1 -1103 -111 +107 [2] [Total: 12] 6

3 (a) (i) Calcium is a fairly soft, silvery-grey metal which quickly tarnishes in air; hence metallic calcium has no commercial uses. However titanium is a commercially important engineering metal. State two physical properties which make titanium a very useful material in the aircraft industry and suggest another property that allows titanium to be used in artificial hip joints.