MJC 2008 H2 Chem Prelim Paper 1 (questions)

Class Reg Number Candidate Name _____________________________ 17 September 2008 1 hour Paper 1 Multiple Choice Questions Additional Materials Data Booklet INSTRUCTION TO CANDIDATES Write your name, class and register number in the spaces provided at the top of this page. There are forty questions in this section. Answer all questions. For each question, there are four possible answers labelled A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the OMR answer sheet. Read very carefully the instructions on the OMR answer sheet. You are advised to fill in the OMR Answer Sheet as you go along; no additional time will be given for the transfer of answers once the examination has ended. Use of OMR Answer Sheet Ensure you have written your name, class register number and class on the OMR Answer Sheet. Use a 2B pencil to shade your answers on the OMR sheet; erase any mistakes cleanly. Multiple shaded answers to a question will not be accepted. For shading of class register number on the OMR sheet , please follow the given examples: If your register number is 1, then shade 01 in the index number column. If your register number is 21, then shade 21 in the index number column. Meridian Junior College JC2 Preliminary Examination 2008 H2 Chemistry 9746 This question paper consists of 22 printed pages. 1

1 A 10 cm 3 sample ethanethiol was exploded with 80 cm 3 of oxygen according to the given equation CH 3CH2SH + 9 2 O2 → 2 CO 2 + SO2 + 3 H2O The resultant gas mixture is cooled and passed through aqueous sodium hydroxide. What would be the final volume of the resultant mixt ure gases at r.t.p after passing through aqueous sodium hydroxide? A 10 cm3 B 35 cm3 C 45 cm3 D 75 cm3 2 The solubility of a gas in water can be ca lculated using its Henry’s Law constant, Kh, which is defined as: K h = concentration of the gas in water partial pressure of the gas in air The Kh for CO2 is 3.8 x 10-2 mol dm-3 atm-1. In an enclosed system containing car bon dioxide, hydr ogen and nitrogen and argon, the volumes of each gases were found to be 3 dm 3, 1 dm 3, 75 dm 3 and 0.5 dm3 respectively. Using Kh, what is the concentration (in mol dm-3) of dissolved carbon dioxide in water when the total atmospheric pressure is 2 atmospheres? A 1.43 x 10 -3 B 2.87 x 10 -3 C 3.00 x 10 -3 D 1.14 x 10 -1 2

3 Figure 1 shows the first 8 ionisation energies of an element J while Figure 2 shows the boiling point of 8 consecutive elements (including element J). D A With reference to Figure 2, which of the options A, B, C or D corresponds to the boiling point of element J? 4 The structure of tetr asulphur tetranitride, S4N4, is shown below. N S N S S N S N x y Which of the following statement is incorrect about the structure? A There are 8 σ bonds and 4 π bonds in the molecule S4N4. B There are 10 lone pairs of electrons in the molecule S4N4. C Both bond angle x and y are 105°. D All the nitrogen atoms are sp2 hybridised. 5 The molecules listed below ar e of the general formula XY n with n ≥ 2. Which of the following pairs does t he first species have a lar ger Y-X-Y angle than the second species? A XeCl4, PH4 + B NH3, PH3 C BF3, CO3 2- D NCl3, BCl3 3

6 The melting point of 4-ni trophenol is higher than that of 2-nitrophenol. Which of the following best explains the above observations? A 4-nitrophenol has a closer packing in the solid state. B 4-nitrophenol has a larger surface area of contact for hydrogen bonding. C The strength of hydrogen bonding is weaker in 2-nitrophenol. D There is less extensive intermolecular hydrogen bonding in 2-nitrophenol. 7 When a solid X is heated in a closed vessel to a temperature T, it forms two gases Y and Z in the molar ratio of 1:2 according to the equation: 2 X (s) ƒ Y(g) + 2 Z(g); ΔH = 0 In the closed system, the reaction comes to equilibrium. The equilibrium pressure for the above system at temperature T is p kPa. Which of the following statements is correct about the above reaction? A The activation energies for both the forward and reverse reactions are zero. B When temperature T increases, the equilibrium pos ition will shift to the right to absorb the heat, thus, producing more products, Y(g) and Z(g). C The value of K p for the above reaction is 4 27 p3 kPa3. D The rate constants do not vary with temperature. 4

8 For the gaseous reaction 2H 2 (g) + 2NO (g) → 2H 2O (g) + N 2 (g), the rate equation is: r a t e = k [ H 2][NO]2 Which graph would confirm the order of reaction with respect to hydrogen gas given in the rate equation above? A B 0 Rate 0 Rate [H2] [H2] C D Rate [H2] 0 0 Rate [H2] 5

9 The equilibrium constant, Kp, for the following reaction is 4.45 at 25°C: 2HI(g) ƒ H2(g) + I2 (g) A mixture initially cont aining one mole each of H I (g) and I2 (g) at 1 atm is allowed to reach equilibrium in a vessel with constant volume. What is the partial pressure of H2 (g) at equilibrium at 25 °C? A 0.17 atm B 0.21 atm C 0.34 atm D 0.78 atm 10 Two cells, one containing a molt en chloride of manganese and the other containing molten chromium (III) chloride were conn ected in series. 33.0g of manganese and 20.8g of chromium were liberated. What is the oxidation state of manganese ion in the chloride? A +2 B +3 C +4 D +5 11 The K b of a weak base is 1.80 x 10 -6 mol dm -3. What would be the pH of the buffer solution formed by mixing 150 cm 3 of 0.10 mol dm -3 of the weak base and 100 cm3 of 0.20 mol dm-3 of its conjugate acid together? A 4.6 B 5.9 C 8.1 D 9.4 6

12 Dinitrogen oxide is formed by the reacti on of nitrogen m onoxide and hydrogen gas according to the following equation: 2 NO(g) + H2(g) ƒ N2O(g) + H2O (g) Which one of the following changes, whil e keeping the pressure constant, is most likely to decrease the entropy of this gaseous system? A increase the temperature B remove H2O (g) from the system C add an inert gas into the system D add more NO gas into the system 13 An experiment is carried out with the following cell. Fe (s) | Fe2+ (aq) || Ni2+ (aq) | Ni (s) The following graph of cell potential ag ainst time was obtained when a change was continuously made to the half-cell. Cell Potential / V Time / s What continuous change c ould produce these results? A add nickel (II) chloride to the nickel half-cell B add aqueous cyanide ions to the iron half-cell C add water to the nickel half-cell D Increases the surface area of iron immersed in the solution. 7

14 A cell is constructed with zinc and ca rbon electrodes, each we ighing 40g, partly immersed in aqueous KOH. Oxygen is suppli ed in the half-cell containing the carbon electrode by bubbling air into it. W hen connected in a circuit, some zinc passes into the solution as zincate (II) ions, ZnO2 2-(aq). The electrode reactions can be presented as shown: Anode : Zn(s) + 4OH -(aq) → ZnO2 2-(aq) + 2H2O(l) + 2e Cathode : O 2 (g) + 2H2O(l) + 4e → 4OH-(aq) The cell delivers a current of 13.7 mA. The zinc electrode is replaced once 60% of it is used up. What is the quantity of el ectricity required to pass through the cell and the time taken before replacement of zinc electrode becomes necessary? Quantity of electricity / C Time / s A 7.08 x 104 5.17 x 106 B 1.18 x 105 8.63 x 106 C 1