2023 TMJC H2 Chem Prelim P2 (QP)

2023 H2 Chem Prelim P2 (QP) 1 The Periodic Table shows many interesting and recurring trends. (a) The variation of 1st ionisation energies across Period 4 is similar to that of Period 3. Table 1.1 shows the 1st ionisation energies of six consecutive elements in Period 4. Table 1.1 element Ga Ge As Se Br Kr 1st ionisation energy / kJ mol–1 580 760 950 1140 1350 (i) Explain why the 1 st ionisation energies show a general increase from gallium to krypton. ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ ....................... [2] (ii) Using your knowledge of the variations, c omplete Table 1.1 with a suggested value for the first ionisation of selenium. [1] (b) Electrical conductivity is measured in Siemens per meter, S m –1, where a higher value represents higher electrical conductivity. Calcium is a Group 2 metal and has an electrical conductivity of 2.9 × 107 S m–1 while copper is a transition metal and electrical conductivity of 5.9 × 107 S m–1. (i) State the full electronic configuration of copper. ................................ ................................ ................................ ....................... [1] (ii) Explain the difference in electrical conductivity between calcium and copper. ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ ....................... [2]

2 2023 H2 Chem Prelim P2 (QP) Tampines Meridian Junior College 2023 JC2 Preliminary Examination H2 Chemistry (c) Other transition metals such as nickel and platinum are sometimes found in copper ores. To obtain pure copper, the ore was made the anode of an electrolysis cell, with a pure copper cathode and aqueous CuSO4 as electrolyte. Explain, with reference to relevant E⦵ values from the Data Booklet what happens to the platinum impurities during this purification procedure. You should also use the following information: Pt2+ + 2e Pt E⦵= +1.20 V ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ [2] (d) Propene undergoes reaction with Br 2 to form 1,2 -dibromopropane. This reaction mechanism features a carbocation intermediate. (i) Draw a labelled diagram to show orbital overlap in the C=C double bond of propene. [2]

3 Tampines Meridian Junior College 2023 JC2 Preliminary Examination H2 Chemistry [Turn over (ii) Name and draw the mechanism of the reaction between propene and Br2 to form 1,2-dibromopropane. Show all charges and relevant lone pairs and show the movement of electron pairs by using curly arrows. [3] (iii) Hence, draw the dot -and-cross diagram for the carbocation intermediate in the mechanism drawn in (ii). State the shape and bond angle at the positively charged carbon in the carbocation intermediate. shape: ................................ ................................ ................................ .................. bond angle: ................................ ................................ ................................ .... [3] [Total: 16]

4 2023 H2 Chem Prelim P2 (QP) Tampines Meridian Junior College 2023 JC2 Preliminary Examination H2 Chemistry 2 Nitrosyl fluoride, NO 2F, is a colourless gas which is used as a nitrating agent in organic synthesis. (a) NO2F is formed from the reaction between nitrogen dioxide and fluorine according to the following reaction. 2NO2(g) + F2(g) 2NO2F(g) The reaction kinetics for this reaction was studied. The experimental rate equation for this reaction can be expressed as rat e = k [NO2]m[F2]n, where m and n are non -zero constants. The concentration of NO2 gas was determined at regular time intervals as the reaction progressed. In this experiment, the concentration of NO 2 and F2 used were at 0.08 0 mol dm −3 and 1.20 mol dm−3 respectively. The results obtained are shown in Fig. 2.1. Fig. 2.1 (i) Using Fig. 2.1, determine the value of m. Show all your working and any construction lines clearly on your graph. [2] ⎯⎯ → 0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.080 0.090 0 50 100 150 200 250 300 350 400 450 500 550 600 [NO2]/ mol dm−3 Time/ s

5 Tampines Meridian Junior College 2023 JC2 Preliminary Examination H2 Chemistry [Turn over (ii) Hence, sketch on the given axes, a graph to show how the rate of reaction changes with concentration of NO2. [1] (iii) Determine the initial rate using the graph in Fig 2.1. [1] (iv) Hence, or otherwise, calculate the value of the rate constant and its units, g iven that the value of n = 1. [2] rate [NO2] 0

6 2023 H2 Chem Prelim P2 (QP) Tampines Meridian Junior College 2023 JC2 Preliminary Examination H2 Chemistry (v) The experiment was repeated using a larger concentration of 1.80 mol dm–3 for F2 instead. Determine the half-life of NO2 in this experiment. [1] (b) NO2 is among the exhaust gases produced by petrol-driven cars. Catalytic converters are fitted in petrol-driven cars to reduce the emission of these harmful NO and NO2 gases by converting them to less harmful products such as H 2O and N 2. Platinum is used as a catalyst inside the catalytic converter. (i) Name the type of catalysis that occurs in the catalytic converter. Outline the mode of action of the platinum catalyst in the reaction. ................................ ................................ ................................ ............................ ................................ ................................ ................................ ............................ ................................ ................................ ................................ .....................