RJC Chemistry H1 P2 with Ans Prelims

©RJC 2008 [Turn over 1 RAFFLES JUNIOR COLLEGE PRELIMINARY EXAMINATION 2008 Higher 1 CANDIDATE NAME C L A S S I N D E X N U M B E R CHEMISTRY 8872/02 Paper 2 15 September 2008 2 hours Candidates answer Section A on the Question Paper. Additional Materials: Answer Paper Data Booklet READ THESE INSTRUCTIONS FIRST DO NOT open this question booklet until you are told to do so. Write your name, class and index number in the spaces provided on the cover page. 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 paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer two questions on separate answer paper. A Data Booklet is provided. Do not write anything on it. You are reminded of the need for good English and clear presentation in your answers. At the end of the examination, 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 B6 /20 B7 /20 B8 /20 Total /80 This question booklet consists of 12 printed pages.

©RJC 2008 [Turn over 2 Section A Answer all questions in this section in the spaces provided. 1 (a) To determine the concentration of lead( II) ions in a sample of lead( II) nitrate solution, 25.0 cm 3 of the solution was added to 40.00 cm 3 of 0.400 mol dm −3 hydrochloric acid. Lead( II) chloride was precipitated out and the mixture was filtered. It was found that 25.0 cm 3 of the filtrate required 27.45 cm 3 of 0.150 mol dm −3 silver nitrate solution for complete reaction. Calculat e the concentration of lead( II) ions in the lead(II) nitrate solution. [4] (b) Sodium nitrite, NaNO 2, is used as a preservative in meat products such as frankfurters and bologn a. In an acidic solu tion, nitrite ion, NO 2 −, is oxidised to nitrate ion, NO 3 −, when it reacts wit h the manganate(VII) ion, MnO4 −. A 1.00 g sample of a water-soluble solid containing NaNO2 was dissolved in dilute H 2SO4 and titrated with 0.0100 mol dm −3 aqueous KMnO 4 solution. The titration required 12.15 cm 3 of the KMnO4 solution. (i) Write an equation for the reaction between MnO 4 − and NO2 −.

©RJC 2008 [Turn over 3 (ii) Calculate the percentage by mass of NaNO 2 in the 1.00 g sample. [4] [Total: 8] 2 (a) The identities of three unknown elements X, Y and Z are rubidium (Rb), strontium (Sr) and caesium (Cs) but not necessarily in that order. The order of the elements in order of increasing first ionisation energy is X < Y < Z. (i) Suggest the ident ity of each element X, Y and Z. [1] (ii) Explain why the first ioni sation energy of element X is smaller than the first ionisation energy of element Y. [2] (iii) Explain why the first i onisation energy of element Y is smaller than the first ionisation energy of element Z. [5]

©RJC 2008 [Turn over 4 (b) The following parts are about the chemistry of Period 3 elements and their compounds. (i) Complete the sketch for the variation in pH of the aqueous solution of chlorides of the following elements. pH of the chorides Na Mg Al Si P [1] (ii) With the aid of relevant equatio ns, briefly explain the shape of your sketch in (i). [3] (iii) Aluminium oxide is amphoteric. Explain what the word in italics means. [1] [5] [Total: 10]

©RJC 2008 [Turn over 5 3 (a) Define the term standard enthalpy change of neutralisation. [1] (b) 10.0 cm 3 of 1.00 mol dm–3 barium hydroxide was added to 50.0 cm 3 of 0.400 mol dm –3 hydrochloric acid. Calcul ate the temperature change given that the enthalpy change of reaction between aqueous barium hydroxide and hydrochlor ic acid is –114 kJ mol–1 and the amount of heat energy required to raise the temperature of 1 cm 3 of solution by 1 K is 4.20 J. [3] (c) Draw an energy profile of the reaction in (b), showing clearly the activation energy and the enthalpy change of the reaction. [2]

©RJC 2008 [Turn over 6 [Total: 6] 4 (a) The reaction between X and Y can be represented by the following equation: X(aq) + 2Y(aq) ⎯→ Z1(aq) + Z2(g) To study the kinetics of the ab ove reaction, two experiments were carried out in the presence of excess X. The experimental results obtained are graphically represented below. Note: [ X] 0 = initial concentration of X(aq) 0.0020 0.0040 0.0060 0.0080 0 0.010 0.020 rate of reaction/mol dm-3 min-1 [Y(aq)]/mol d 0 m-3 Experiment 1 [X]0 = 1.50 m Experiment 2 [X] 0 = 0.50 m ol dm-3 ol dm-3 [X]0 = 1.50 mol dm–3 [X]0 = 0.50 mol dm –3 [Y(aq)]/mol dm –3 (i) Explain what is meant by order of reaction with respect to X. [1] (ii) With the aid of the graph, dete rmine the order of reaction with respect to each of the two reactants, X and Y.

©RJC 2008 [Turn over 7 [3] (iii) Hence write down the rate equat ion for the reaction and state the units for the rate constant k. [5] (b) With the aid of a sketch of the Boltzmann distribution, state and explain the effect of an increase in temper ature on the rate of a chemical reaction. [3] [Total: 8]

©RJC 2008 [Turn over 8 5 For the reaction scheme below, give the reagents and conditions for steps I to III in the table provided, and draw the structural formulae of A to E in the boxes provided 2,4–DNPH C8H7O2Na E Step II Oxidation B C 9H10 C9H12O A COOH COOH Step I H2SO4, K2Cr2O7, heat C9H10O C C H3 OH CH3 NC C Ste III p I2, NaOH, warm I2, NaOH, warm C15H14N4O4 Reagents & Conditions Step I Step II Step III D [Total: 8]

©RJC 2008 [Turn over 9 Section B Answer two of the three questions in this section on separate paper. 6 (a) With the crude oil prices hitting over US$100 a barrel, many motorists are opting for lower octane rating petrol to make ends meet. The octane rating of a fuel is the knock resistance (anti-knock rating) compared to a mixture of an isom er of octane and heptane. As octane has a total of 18 isomers, It is us eful to study how these isomers may be used to derive cheaper but yet acceptable knock resistance fuel. Isomers of octane may also be di stinguished by t he number of mono- brominated products formed upon reaction with bromine. (i) Name the reaction mechanism of the above reaction of octane with bromine. State the reagents and conditions required. [2] (ii) Draw an isomer of octane which reacts with limiting bromine to give (1) only one mono–brominated product (2) three mono–brominated products [2] (iii) State the type of isomerism exhibited by your answers to (ii). [1] (iv) State which isomer, (1) or (2), has a higher boiling point. [1] [6] (b) To combat pollution and soaring fuel cos t, luxury sports car maker Ferrari is experimenting with ethanol to help produce cars with lower carbon dioxide emissions and improv ed fuel economy. Titled “Drunk with Power”, this projec t using ethanol as fuel also claims to bring about an increase in the horsepower of the automobile t