TJC_H2_CHEM_P3_W_MARK_SCHEME Prelim

9647/03/TJC Prelim 2011 [Turn Over 1 CHEMISTRY (H2) 9647/03 Paper 3 Free Response Tuesday 13th September 2011 2 hours Candidates answer on separate paper. Additional materials: Answer paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, Civics Group and Index number in the spaces provided on the cover page provided and 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 any four questions. A Data Booklet is provided. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in bracke ts [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together. This question paper consists of 11 printed pages.

9647/03/TJC Prelim 2011 [Turn Over 2 Answer any four questions. 1. (a) Nitrogen is chemically unreactive and will only react with oxygen under high temperatures to produce various atmospheric pollutants, such as nitrogen monoxide and nitrogen dioxide. The table below shows the standard enthalpy change of formation of some nitrogen oxides. Oxide NO NO 2 N 2O H f / kJ mol1 +90.4 +33.9 +81.6 (i) Determine the density, in g cm3, of nitrogen dioxide gas at room temperature and pressure. (ii) Nitrogen dioxide and dinitrogen oxide can react to give nitrogen monoxide: NO2(g) + N2O(g)  3NO(g)  S r = +171.4 J K1 mol1 By using the data provided above, calculate the G for the above reaction at 800 K and hence predict if the reaction is spontaneous at 800 K. Assume that H f and S r do not change with temperature. (iii) Dinitrogen oxide, N 2O, is a colourless gas and is also known as laughing gas. Draw a ‘dot-and-cross’ diagram to illustrate the type of bonding present within the N 2O molecule, where nitrogen is the central atom. Name the shape of the molecule. [7] (b) A solution contains 1.0  102 mol dm3 of silver ions and 2.0  102 mol dm3 of lead(II) ions. When an aqueous solution containing chloride ions is added to the solution, both silver chloride (Ksp value = 1.8  1010) and lead(II) chloride (Ksp value = 1.7  105) precipitate from the solution. Determine which salt precipitates first and the concentration of chloride which is necessary to begin the precipitation of each salt. [3] (c) Explain the following observations with the aid of relevant equations. (i) The second ionisation energies of the Group II elements decrease down the group. (ii) Magnesium nitrate produces a brown gas on gentle heating whereas barium nitrate gives a brown gas on