NJC Prelim CHEM P1

1 NJC Preliminary Examination 9647/01/15 [Turn Over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 1 Multiple Choice Additional Materials: Multiple Choice Answer Sheet Data Booklet 9647/01 Thu 17 Sep 2015 1 hour READ THESE INSTRUCTIONS FIRST Write in soft pencil. Write your name, subject class and registration number on the Optical Answer Sheet (OAS) in the spaces provided unless this has been done for you. There are 40 questions in this paper. Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider correct and record your choice in soft penci l on the separate Optical Answer Sheet. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet. This booklet consists of 19 printed pages and 1 blank page.

2 NJC Preliminary Examination 9647/01/15 [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 When scientists research on atomic nuclei, they often correlate the stability of isotopes with the proton to neutron ratio. Which isotope has the same proton to neutron ratio as 18 8 O? A 9 5 B B 26 12 Mg C 36 16 S D 52 24 Cr 2 AxOy, a gaseous oxide of an element A, gives an acidic gas AO2, on combustion with excess oxygen. When 10 cm 3 of AxOy is burnt in 40 cm 3 oxygen (in excess), the total volume of gas after cooling to the original temperature is unchanged. On shaking with excess aqueous potassium hydroxide, the volume is reduced to 20 cm3. All volumes are measured at the same temperature and pressure. What are the values of x and y? x y A 1 1 B 2 3 C 3 2 D 3 4

3 NJC Preliminary Examination 9647/01/15 [Turn Over 3 The diagram below shows the first ionisation energy of some element s with atomic numbers less than 20. Which is the most likely formula of the chloride of L and M? A LCl B LCl5 C MCl2 D MCl5 4 The figure below shows the stable oxidation numbers of five consecutive elements, P to T, plotted against their atomic numbers. What are the likely atomic numbers of P to T? A 1 to 5 B 3 to 7 C 11 to 15 D 19 to 23 first ionisation energy L M atomic number

4 NJC Preliminary Examination 9647/01/15 [Turn Over 5 When a sample of gas is compressed at constant temperature from 20 atm to 80 atm, its volume changes from 67.0 cm3 to 15.5 cm3. Which is a possible explanation of this behaviour? A The gas particles are adsorbed onto the vessel walls. B The gas particles dimerised. C The gas particles dissociated. D The gas is liquefied at 80 atm. 6 The shapes of two species, D and E, are linear and T-shaped respectively. What could D and E be? D E A SO2 BH3 B I3  BrCl3 C CS2 AsCl3 D H2S ICl3 7 Some enthalpy changes of combustion are given below. Hc / kJ mol1 CO(g) + 2 1 O2(g)  CO2(g) 283 H2(g) + 2 1 O2(g)  H2O(l) 286 CH3OH(l) + 2 3 O2(g)  CO2(g) + 2H2O(l) 715 What is the enthalpy change of the following reaction? CO(g) + 2H2(g)  CH3OH(l) A 146 B 140 C +140 D +146

5 NJC Preliminary Examination 9647/01/15 [Turn Over 8 When a large current was passed through acidified aqueous nickel(II) sulfate, there was a simultaneous liberation, at the cathode, of x mol of a grey solid and y dm3 of a diatomic gas (measured at s.t.p.). How many moles of electrons passed through the cell? A 𝑥 + 𝑦 22.4 B 𝑥 + 𝑦 11.2 C 2𝑥 + 𝑦 22.4 D 2𝑥 + 𝑦 11.2 9 The equation below shows the reaction of ethanoic acid with ethanol. CH3CO2H(l) + C2H5OH(l) CH3CO2C2H5(l) + H2O(l) ethyl ethanoate Which statement is true when the above reaction has attained equilibrium? A The equilibrium constant, K, is equal to 1. B The reaction between the acid and the alcohol has stopped. C The concentrations of the products and reactants are the same. D The rate of formation and the rate of hydrolysis of ethyl ethanoate are the same. 10 A student wanted to determine the equilibrium constant for the decomposition of calcium carbonate, CaCO 3. He sealed 2.0 g of CaCO 3 in an evacuated 2 .0 dm 3 metal flask and connected a pressure gauge to the flask. The flask was placed in an oven and heated to a temperature of 800 oC, at which an equilibrium was reached according to the following equation: CaCO3(s) CaO(s) + CO2(g) When the equilibrium was established, 1.40 x 102 mol of CO2 was present in the flask. What is the value of equilibrium constant, Kc, for this reaction at 800 °C? A 3.27 x 102 B 1.63 x 102 C 1.40 x 102 D 7.00 x 103

6 NJC Preliminary Examination 9647/01/15 [Turn Over 11 Water dissociates into ions according to the following equilibrium. H2O(l) H+(aq) + OH–(aq) ∆Ho = +57 kJ mol−1 at 25 °C Which statement is not true as temperature rises? A The pH of water decreases. B The dissociation constant of water increases. C The extent of dissociation of water increases. D The concentration of H+(aq) is higher than that of OH–(aq). 12 The distribution of the number of molecules with energy E is given in the sketch below for two temperatures, T1, and a higher temperature T2. The letters P, Q, R refer to the separate and differently shaded areas. The activation energy is marked on the energy axis. Which is the fraction of the molecules with energy larger than the activation energy at T2? A P Q B P R Q  C Q P R Q   D R Q P R Q   number of molecules with energy E T1 T2 energy E activation energy region P region Q region R Legend

7 NJC Preliminary Examination 9647/01/15 [Turn Over 13 A diagonal relationship is said to exist betw een certain pairs of diagonally adjacent elements in the second and third periods of the Periodic Table. One such pair is beryllium and aluminium, where they share similar chemical properties. Which is not a property of the compounds of beryllium? A Beryllium chloride has a high melting point. B Beryllium chloride can form the dimer Be2Cl4. C Effervescence is observed when aqueous sodium carbonate is added to beryllium chloride. D Beryllium oxide reacts with carbon dioxide to form a salt. 14 The graphs below show the variation of two properties of some Period 3 elements and their compounds. Which of the following correctly describes properties A and B? Property A Property B A enthalpy change of vapourisation of the elements pH of the oxides when added to water B first ionisation energy of the elements enthalpy change of vapourisation of the elements C enthalpy change of vapourisation of the chlorides electrical conductivity of the elements D electrical conductivity of the elements pH of the chlorides when added to water

8 NJC Preliminary Examination 9647/01/15 [Turn Over 15 Which statement about the compounds of Group VII elements is incorrect? A The oxidising power of halogens decreases down the group. B The Ksp value of silver halides decreases down the group. C The magnitude of