VJC 2021 Prelim H2P2 Qns [FInal]

1 Ó VJC 2021 9729/02/PRELIM [Turn over CANDIDATE NAME CT GROUP VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATIONS Higher 2 ……………………………………………….………….. …………………………….. CHEMISTRY 9729//02 Paper 2 Structured Questions Candidates answer on the Question Paper. 15 September 2021 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your index number, name and CT group in the spaces at the top of this page. Write in dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /10 2 /15 3 /10 4 /15 5 /12 6 /13 Total /75 This document consists of 22 printed pages and 2 blank pages.

2 Ó VJC 2021 9729/02/PRELIM [Turn over 1 The table below shows the fifth to eighth ionisation energies of two consecutive elements, X and Y in the second period of the Periodic Table. successive ionisation energies / kJ mol–1 5th 6th 7th 8th X 10990 13330 71330 84080 Y 11020 15160 17870 92040 (a) (i) With the aid of an equation, define the term first ionisation energy with reference to X. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… ………………………………………………………………………………………....... ………………………………………………………………………………………....... ………………………………………………………………………………………....... [2] (ii) State and explain the group number of X. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… [1] (b) (i) Write down the full electronic configurations of X+ and Y+. X+: ………………………………. Y+: ………………………………. [1]

3 Ó VJC 2021 9729/02/PRELIM [Turn over (ii) Hence, explain which element has a less endothermic second ionisation energy. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… ………………………………………………………………………………………....... ………………………………………………………………………………………....... [2] (c) Boron is another Period 2 element which reacts vigorously with fluorine to form boron trifluoride, BF3, an important reactant in organic syntheses. Boron trifluoride is a very reactive gas and it is hard to handle at room temperature. It can be converted to a liquid compound which is easily stored by reacting it with diethyl ether in the mole ratio of 1:1. Diethyl ether can be represented by the formula ROR, where –R represents the ethyl group. (i) Explain why boron trifluoride can form a compound with diethyl ether. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… ………………………………………………………………………………………....... …………………………………………………………………………………………… …………………………………………………………………………………………… ………………………………………………………………………………………....... ………………………………………………………………………………………....... [2]

4 Ó VJC 2021 9729/02/PRELIM [Turn over (ii) Draw the structure of the compound formed, indicating clearly the shape and bond angle around each central atom. [2] [Total: 10] 2 (a) Use of the Data Booklet is relevant to this part of the question. Xenon hexafluoride, XeF6 was one of the first noble gas compounds synthesised. XeF6 reacts with the silicon dioxide, SiO2, in glass to form liquid xenon oxytetrafluoride, XeOF4 and gaseous silicon tetrafluoride, SiF4 as shown by the equation below: 2XeF6 + SiO2 ® 2XeOF4 + SiF4 (i) An unknown amount of XeF6 was allowed to react with silicon dioxide in a 2 m3 closed vessel at 25 ºC. When all the XeF6 has reacted, a pressure of 0.505 kPa was measured in the vessel. Assuming that the gas inside the vessel behaves ideally, calculate the amount of XeF6 reacted in the vessel. [2]

5 Ó VJC 2021 9729/02/PRELIM [Turn over (ii) Hence, calculate the mass of XeF6 reacted. [1] (b) In a given vessel of a fixed volume, N2O5 gas decomposed to NO2 and O2 as shown below at 50 oC. 2N2O5(g) ® 4NO2(g) + O2(g) The rate equation for this thermal decomposition is as follows. Rate = k[N2O5] Theory shows that under the conditions of the experiment, the following relationship between the concentration of N2O5 and time is as follows. equation 1 ln[N2O5]t = –kt + ln[N2O5]initial where [N2O5]t = concentration of N2O5 present at time t k = rate constant (i) The following graph of ln[N2O5]t against t is plotted with the data obtained from the experiment. –4.0 4.04 –4.2 4.04 –4.4 4.04 –4.6 –4.8 –5.0 4.04 –5.2 4.04 0 600 1200 1800 2400 3000 3600 Time / s 4.04.0 ln[N2O5]t

6 Ó VJC 2021 9729/02/PRELIM [Turn over With the help of equation 1 and the graph above, determine I. the initial concentration of N2O5 II. rate constant, k, including its units [2] (ii) It is known that the rate of the reaction doubles with every 10 oC rise in temperature. Calculate the initial rate of the thermal decomposition of N2O5 when the volume of vessel is halved at 70 oC. [2]

7 Ó VJC 2021 9729/02/PRELIM [Turn over (c) In another experiment, O2 reacts with NO as follows. O2 + 2NO ® 2NO2 (i) Using the following data, determine the order of reaction with respect to O2 and NO. Hence, write down the rate equation for the reaction. [2] experiment [O2] / mol dm–3 [NO] / mol dm–3 initial rate / mol dm–3 s–1 1 1.10 x 10–2 1.30 x 10–2 3.21 x 10–3 2 2.20 x 10–2 1.30 x 10–2 6.40 x 10–3 3 1.10 x 10–2 2.60 x 10–2 12.8 x 10–3 (ii) The following relationship can be used to calculate the activation energy of the reaction between O2 and NO: ln= –(– ) where k = rate constant at the respective temperature in Kelvins. Calculate the activation energy of the reaction if the values of the rate constants are 7.00 x 1