SAJC Prelim P2

ST. ANDREW’S JUNIOR COLLEGE Higher 1 PRELIMINARY EXAMINATION 2009 Name Class CHEMISTRY PAPER 2 Candidates answer Section A on the Question Paper. 8872/ 02 15 September 2009 2 hours Additional Materials: Writing paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer any two questions on separate writing paper. A Data Booklet is provided. At the end of the exam, fasten all your work securely together. The number of marks is given in brackets [] at the end of each question or part question. For examiner’s use Section A / 40 B9 B10 B11 Total / 80 This paper consists of 16 printed pages and 1 blank page.

2 BLAN K PAGE

3 Section A Answ er all questions. 1 The use of the Data Booklet is relevant to this question. (a) (i) Define relative atomic mass. [1] (ii) Gallium is in Group III and is found below aluminium in the Periodic Table. Gallium has 2 isotopes. One of the isotopes, 69Ga has a relative abundance of 64.0%. Calculate the relative isotopic mass of the other gallium isotope, to the nearest whole number. [1] (b) Acidified potassium manganate(VII) oxidises ethanedioic acid, H2C2O4 to form carbon dioxide gas according to the following ionic equation: C2O4 2-  2CO2 + 2e 1.07 g of impure sample of H2C2O4 was made up to 250 cm3 of solution. 25.0 cm3 of this solution reacted completely with 25.60 cm3 of 0.02 mol dm-3 acidified KMnO4 solution. (i) Write an overall ionic equation for the reaction between H2C2O4 and KMnO4. [1] [Turn Over

4 1 (b) (ii) Hence, determine the percentage purity of the ethanedioic acid. [2] [Total: 5 ] 2 The first 8 ionisation energies of an element, W, is shown in the table below. Electron 1 2 3 4 5 6 7 8 Ionisation energy/ kJ mol -1 572 890 1250 2249 4973 6152 9945 11012 (a) Deduce which group element W belongs to. Explain your answer. [2] (b) (i) Suggest the formula of the oxide of W and predict the type of bonding present in the oxide of W. [1] Formula: __________ Type of bonding: ______________ (ii) Suggest a pH value for the resulting solution obtained when the oxide of W is dissolved in water. [1] [Total: 4]

5 3 Oil of wintergreen is a common active ingredient in muscle rubs. It has the following structure. C O O CH3 2 OH 1 (a) State the type of hybridisation of the carbon atoms, C1 and C2. [2] C1: __________ C2:___________ (b) State the shape and the bond angle around carbons C1 and C2. [2] Carbon Shape Bond angle C1 C2 (c) Sketch the shape of one hybrid orbital of the carbon C1. [1] [Total: 5] [Turn Over

6 4 2-methylpro pene is a gas used in the manufacture of poly-isobutylene. (a) (i) Define standard enthalpy change of formation, with reference to 2-methylpropene. (ii) Write the equation which represents the standard enthalpy change of formation of 2-methylpropene, showing the structural formula of 2-methylpropene. [2] (b) Use the following standard enthalpy changes of combustion, ∆H c°, to calculate the enthalpy change of formation of 2-methylpropene: Compound ∆Hc°/ kJ mol-1 Carbon -393 Hydrogen -286 2-methylpropene -2520 [2] [Total: 4]

7 5 An excess of small pieces of calcium carbonate was allowed to react with 100 cm3 of 0.1 mol dm-3 hydrochloric acid. The volume of carbon dioxide formed during the experiment is shown on the graph below. (a) Determine the order of reaction with respect to hydrochloric acid. (b) On the axes above, sketch and label the curves for the following experiments that were carried out at the same temperature as the original experiment: (i) 100 cm3 of 0.05 mol dm-3 hydrochloric acid with an excess of small pieces of calcium carbonate. (ii) 120 cm3 of 0.1 mol dm-3 hydrochloric acid with an excess of small pieces calcium carbonate. [4] [Total:4] [Turn Over 25 35 4030 45 50 Time / s201510 5

8 6 X and Y were mixed in a closed vessel and the whole system was allowed to reach equilibrium, as shown in the following equation: X (g) + Y (g) 2Z (g) The concentrations of all gases were measured at one-minute interval for 4 minutes, and then one of the operating conditions were altered. The effects were shown graphically below. (a) Write an expression for the equilibrium constant, K C, and hence calculate its value at the 3rd minute. (b) Suggest the change that could have occurred at the 4 th minute. (c) Sketch on the graph above the changes in the concentrations of X, Y and Z when the pressure of the system is halved at the 7th minute. [4] [Total: 4] Concentration / mol dm-3 0 0 0 0 0 0 0.10 0.09 .08 .07 .06 .05 .04 .03 0.02 0.01 0 0 1 2 3 4 5 6 7 [Z] [Y] [X] [X] [Y] [Z] Time / min 8 9 10

9 7 (a) Define the term buffer solution. [2] (b) Given the following reaction: H2O + H2PO4 - HPO4 2- + H3O+ Explain, with the aid of suitable equations, how the above system acts as a buffer upon the addition of: (i) H+ ions and (ii) OH- ions. [2] [Total: 4] [Turn Over

10 8 (a) In the space s provided below, draw the organic product formed when compound A is reacted with each of the following reagents. Compound A Reagent Organic product formed (i) Heat with ammonia dissolved in ethanol in a sealed tube (ii) Acidified potassium dichromate(VI) (aq) with distillation (iii) Hot aqueous sulfuric acid [3]