NJC H2 Chem 2012 Prelim P1 QP

1 NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAM Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY 9647/01 Paper 1 Multiple Choice Fri 21 Sept 2012Additional Materials: Multiple Choice Answer Sheet 1 hourData Booklet READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, highlighters, glue or correction fluid. Write your name, subject class and registration number on the Answer Sheet in the spaces provided unless this has been done for you. There are 40 questions on 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 pencil on the separate Answer Sheet. Read the instructions on the Answer Sheet very carefully. 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 paper consists of 18 printed pages and 0 blank page. NJC/H2 Chem/01/2012 [Turn over

2 NJC/H2 Chem/01/2012 [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 Which atom has the highest ratio of unpaired electrons to paired electrons in its ground state? A boron B carbon C nitrogen D oxygen 2 Bombardment of 14N with a-particles (helium nuclei) produces a hydrogen nucleus and another nucleus. This other nucleus is A 14C6 B 14N7 C 17O8 D 18Ne10 3 The successive ionisation energies (kJ mol ─1) of two elements are given below: X 1012 1907 2914 4964 6274 21267 26431 29876 35905 Y 1251 2298 3822 5159 6542 9362 11108 33604 38860 Which of the following statements is false? A The formula of the compound formed between X and Y is XY 3. B The compound formed between X and Y is covalent. C X has a giant covalent structure. D Y exists as diatomic molecules. 4 When the N2+ ion is formed from N2, a σ bonding electron is removed. Which statement is correct? A The bond order decreases so N2+ has a stronger, shorter bond than N2. B The bond order decreases so N2+ has a weaker, longer bond than N2. C The bond order increases so N2+ has a stronger, shorter bond than N2. D The bond order increases so N2+ has a weaker, longer bond than N2.

3 NJC/H2 Chem/01/2012 [Turn over 5 In which pair of species are the values of the bond angles the closest? A BF3 and NH3 B CH3‒ and BF3 C H2O and C2H4 D NH4+ and SO42‒ 6 10 cm3 of hydrocarbon is burnt in 100 cm3 of excess oxygen at room temperature. The final volume of gas mixture is 85 cm 3. When the gas mixture is bubbled through aqueous sodium hydroxide solution, the volume of gas mixture decreases to 55 cm 3. What is the formula of the hydrocarbon? A C3H6 B C3H8 C C6H12 D C6H14 7 Use of the Data Booklet is relevant to this question. The graph represents the variation of a property of the Group II elements. What is this property? A ionic radius B ionisation energy C neutron / proton ratio D rate of reaction with water property

4 NJC/H2 Chem/01/2012 [Turn over 8 The diagram shows bond energies in halogen molecules. Why does the value for fluorine not follow the trend shown by chlorine, bromine and iodine? A Fluorine is more electronegative than the other halogens. B Lone electron pairs in fluorine repel more strongly than those in the other halogens. C The bonds in fluorine are more polar than those in the other halogens. D The bonds in fluorine have some π-character. 9 What is the pressure (in Pa) of a sample of hydrogen gas that has density of 8 gm ─3 at 300 °C? A 273 10 101 22.44573 3´ ´ ´ ´ B 273 1014 .228573 ´ ´ ´ C 573 10 1012 .114273 3´ ´ ´ ´ D 273 1012 .118573 ´ ´ ´

5 NJC/H2 Chem/01/2012 [Turn over 10 The rate equation for the reaction S2O82− (aq) + 2 I− (aq) → 2SO42− (aq) + I2(aq) is rate = k[S2O82−][I−] where k , the rate constant is found to be 0.2 mol −1 dm3 s −1 at temperature t. What is the half-life of the reaction when S 2O82− is present in a large excess at a concentration of 0.5 mol dm−3 at the same temperature t? A 0.7 s B 1.4 s C 3.5 s D 6.9 s 11 Hess’s Law can be used to calculate the average C–H bond energy in methane. DHoat = standard enthalpy change of atomisation DHof = standard enthalpy change of formation DHoc = standard enthalpy change of combustion Which values of the following data are needed in order to perform the calculation? A DHoc (C), DHoc (H2), DHoc (CH4) B DHoat (C), DHoat (H2), DHof (CH4) C DHoc (C), DHoc (H2), DHof (CH4) D DHof (CH4) only as DHof (C) and DHof (H2) are defined as zero. 12 In a car engine, non-metallic element X forms a pollutant oxide Y. Further oxidation of Y to Z occurs spontaneously in the atmosphere. In this further oxidation, 2 mol of Y reacts with 1 mol of gaseous oxygen. Z can dimerise at specific conditions. Which statement about X, Y and Z is incorrect? A X forms a basic hydride. B Y is a diatomic molecule. C Z is a polar molecule. D Z contributes to global warming.

6 NJC/H2 Chem/01/2012 [Turn over 13 The diagram below represents the reaction profile of the monomer-dimer system: kf kb 2NO2 (g) N2O4 (g) brown colourless Which statement about the equilibrium is correct? A The equilibrium constant K c will be larger at higher temperatures. B kf increases and kb decreases when the equilibrium mixture is heated. C Doubling the total pressure of the system reduces the percentage dissociation to half. D At higher temperature, the colour intensity of the mixture increases. 14 Which of the following statemen ts about the spontaneity of the gas-phase reactio n shown is true at 25 °C? 2 O=N–Cl(g) ® 2 N=O(g) + Cl2(g) A The reaction cannot be spontaneous. B The reaction will be spontaneous regardless of the magnitude of DH and DS. C The reaction will be spontaneous only if the magnitude of DH is large enough to overcome the unfavorable entropy change. D The reaction will be spontaneous only if the magnitude of DS is large enough to overcome the unfavorable enthalpy change. Enthalpy Progress of reaction

7 NJC/H2 Chem/01/2012 [Turn over 15 When a mineral was heated in a Bunsen flame to constant mass, a colourless gas that turned limewater milky was evolved. The remaining solid was cooled and then added to aqueous hydrochloric acid. Vigorous effervescence was seen. What was the mineral? A Dolomite, CaCO 3.MgCO3 B Barytocalcite, BaCO3.CaCO3 C Aragonite, CaCO3 D Artinite, MgCO3.Mg(OH)2.3H2O 16 The following two experiments are carried out with a nhydrous potassium chloride and observations X and Y are made at the end of each experiment. Concentrated sulfuric acid is added to the potassium chloride and the fumes produced are bubbled into aqueous potassium iodide solution