IJC 2015 H1 CHEM P1 Ans Prelims

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2  IJC 2015 Prelim 1/8872/01 [Turn over Section A For each question there are four possible answers, A, B, C, and D. Choose the one you consider to be correct. 1 An exciting chemical demonstration is the ‘barking dog’. An equation which describes the reaction is shown. 6NO + 2CS2 3N 2 + 2CO + 2SO2 + 1 4 S8 Carbon disulfide, CS2, is a liquid with a density of 1.26 g cm3. Which mass of sulfur would be formed from 5.00 cm 3 of CS2 if the reaction proceeded with 80% yield? [Mr of CS2 = 76.2; S8 = 256.8] A 1.67 g B 2.12 g C 2.65 g D 3.32 g 2 The following half-reactions occur when potassium iodate( V), K IO3, in hydrochloric acid solution oxidises iodine to ICl2 . IO3  + 2Cl + 6H+ + 4e ICl2  + 3H2O I2 + 4Cl 2ICl2  + 2e What is the ratio of IO3  to I2 in the balanced chemical equation for the overall reaction? A 1: 1 B 1: 2 C 1:4 D 2 :1 3 Use of the Data Booklet is relevant to this question. In which pairs do both species have different number of unpaired electrons? A O and Cl+ B F+ and Ga C P and Ne+ D Ga+ and Ne

3  IJC 2015 Prelim 2/8872/01 [Turn over 4 The first seven ionisation energies of an element M are shown in the sketch graph. What could be the identity of element M? A aluminium B magnesium C phosphorus D silicon 5 Ions of the two most common isotopes of zinc are shown below: 64 30 2+Zn 66 30 2+Zn Which of the following statements is correct? A Both Zn2+ ions have the same number of electrons but different number of protons. B Both Zn2+ ions have the same electron configuration 1s22s22p63s23p63d84s2. C The 64 30 2Zn  ion has fewer neutrons in its nucleus than the 66 30 2Zn  ion. D The 66 30 2+Zn ion will be deflected more than the 64 30 2Zn  ion in an electric field of the same strength.

4  IJC 2015 Prelim 2/8872/01 [Turn over 6 Refer to the molecule below. Which one of the following shows the correct information with regard to the various labelled bond angles? smallest bond angle  largest bond angle A c d e B d a c C e b a D b e d 7 Three substances, X, Y and Z, have the physical properties shown in the table. substance melting point / °C boiling point / °C density / g cm-3 conductivity (solid) conductivity (liquid) X Y Z 114 993 650 184 1695 1755 4.93 2.56 1.74 poor poor good poor good good What could be the identities of X, Y and Z? X Y Z A I2 SiO 2 Ca B I2 NaF Mg C Si Mg NaF D Ca KCl SiO2 a b c e d

5  IJC 2015 Prelim 2/8872/01 [Turn over 8 Consider the following four compounds. 1 (CH 3)3CH 2 CH 3CH2CH2CH3 3 CH 3CH2CH2OH 4 CH3CH2Cl What is the order of decreasing boiling point of the compounds? A 1 2 4 3 B 3 4 1 2 C 3 4 2 1 D 4 3 2 1 9 What does the following equation represents? H2(g) + O2(g) H 2O2(g) A standard enthalpy change of combustion of H2 B standard enthalpy change of formation of H2O2 C sum of standard enthalpy change of formation of H 2O2 and the enthalpy change of vaporisation of H2O2. D sum of standard enthalpy change of combustion of H 2 and the enthalpy change of vaporisation of H2O2. 10 In an experiment, 1.00 g of solid K 2CO3 was added to a polystyrene cup containing 25.0 cm3 of 1.0 mol dm –3 aqueous HC l. It was found that the temperature of the solution rose by 2.1 oC. The equation for the reaction is as follows. K 2CO3(s) + 2HCl(aq) 2KCl(aq) + CO2(g) + H2O(l) What is the correct value for the enthalpy change of reaction above? (Assume that the heat capacity of the solution is 4.2 J K –1 cm–3) A –8.82 kJ mol–1 B +8.82 kJ mol–1 C –30.5 kJ mol–1 D +30.5 kJ mol–1

6  IJC 2015 Prelim 2/8872/01 [Turn over 11 The decomposition of compound A to form compound B can be represented by the following equation: A(g) 2 B(g) An enclosed system initially containing some quantities of A and B are allowed to reach equilibrium. At t minutes, a change has been introduced to the system. The graphs of the concentrations of A and B against time is plotted. Which of the following could result in the change in concentrations of A and B as represented by the graph at t minutes? A increase in concentration of A B decrease in concentration of A C decrease in volume of the system D decrease in pressure of the system 12 An aqueous solution was prepared containing 1.0 mol of AgNO 3 and 1.0 mol of FeSO 4 in 2.00 dm3 of water. When equilibrium was established, there was 0.44 mol of Ag +(aq) in the mixture. Ag +(aq) + Fe2+(aq) Ag(s) + Fe 3+(aq) What is the numerical value of Kc? A 1.35 B 1.62 C 2.89 D 5.79 Time/ minutes Concentrations / mol dm-3 t 0 A B

7  IJC 2015 Prelim 2/8872/01 [Turn over 13 What is the pH of a solution containing 0.0100 mol dm–3 of Ba(OH)2 at 298K? A 2.0 B 1.70 C 12.0 D 12.3 14 Bromine and methanoic acid react as follows: Br2(aq) + HCOOH(aq) 2Br –(aq) + 2H+(aq) + CO2(g) The rate of reaction is found to be first order with respect to both bromine and to methanoic acid. Which of the following statements about the above reaction is incorrect? A The units of the rate constant is mol –1 dm3 s–1. B The half-life of the reaction can be found using k 2 lnt1/2  . C The rate of formation of H+(aq) is twice the rate of disappearance of Br2(aq). D Doubling the concentration of methanoic acid doubles the rate of evolution of gas. 15 Which of the following elements forms an oxide with a giant structure and a chloride which is readily hydrolysed? A aluminium B carbon C phosphorus D silicon Answer: D Aluminium: Al 2O3 has giant covalent structure and AlCl 3 undergoes partial hydrolysis Carbon: Both oxide and chloride are simple molec