DHS_2008 Prelim - H2 Chemistry Paper 2

This question paper consists of 12 printed pages and 0 blank page. [Turn over CANDIDATE NAME ____________________________ CLASS________ DUNMAN HIGH SCHOOL (SENIOR HIGH) YEAR 6 PRELIMINARY EXAMINATION 2008 H2 CHEMISTRY Paper 2 Structured 9746/02 17 September 2008 1 hour 30 minutes Additional materials: Data Booklet INSTRUCTIONS TO CANDIDATES 1 Write your name and class on this question paper. 2 Answer ALL questions. 3 Write your answers in the spaces provided on the question paper. 4 A Data Booklet is provided. 5 The number of marks is given in brackets [ ] at the end of each question or part question. 6 You may use a calculator. FOR EXAMINER’S USE Question No. 1 2 3 4 5 Total % Marks 17 12 12 9 10 [60]

2 © DHS 2008 9746/02 [Turn over 1(a) The graph below shows the trend in a particular property of Period 3 elements. (i) Label on the y–axis of the graph, the property represented. (ii) Briefly explain the trend of this property. [4] (b) One student, Mr Piah, is given three aqueous solutions of the oxides of three Period 3 elements. He adds the indicator, thymol blue, to the three unknown solutions separately and noted the colours of the solutions. (i) With reference to the pH range and colour of thymol blue indicator, identify each of these solutions in the spaces provided below. pH range pH < 1.2 2.8 < pH < 8.0 pH > 9.6 colour of thymol blue red yellow blue solution colour observed identity of oxide 1 green 2 blue 3 red Ionic radius /nm • • • • • • proton number | 11 | 13 | 14 | 15 | 16 | 17 | 18 | 12 •

3 © DHS 2008 9746/02 [Turn over (ii) Briefly outline the reaction of these oxides with water, supporting your answer with appropriate equations. [4] (c) (i) Solid barium amide, Ba(NH 2)2 decomposes when heated to form a high melting point solid, barium nitride, Ba 3N2, and ammonia gas as the only products. Given that the variation in thermal stability of Group II amides parallels that of Group II nitrates, explain qualitatively whether magnesium amide, Mg(NH 2)2, decomposes at a higher temperature than barium amide.

4 © DHS 2008 9746/02 [Turn over (ii) Magnesium hydroxide is used as an antacid to neutralise stomach acid and as a laxative. It is a sparingly soluble compound with solubility product value of 1.0 x 10 –11. Calculate the solubility of Mg(OH)2 in: (1) Pure water (2) 0.050 mol dm –3 of NaOH (iii) One of the clearest ways in which atomic properties influence chemical behavior appears in the diagonal relationships of elements. One such example is beryllium and aluminium, from Group II and III respectively. Their oxides show similar chemical behaviour towards acids and bases. Write balanced equations to show the reactions of beryllium oxide with the