SRJC 2008 JC2 Prelims H1 Paper 2

© SRJC 2008 8872/02/Prelims/2008 [Turn Over SERANGOON JUNIOR COLLEGE General Certificate of Education Advanced Level Higher 1 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY 8872/02 Preliminary Examination 19 August 2008 Paper 2 2 hr Additional Materials: Data Booklet Writing Papers 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 work. SECTION A : Answer all questions in the space provided. SECTION B: Answer two questions on separate answer paper. At the end of the examination, fasten all your work securely together. The number of marks is given in the brackets [ ] at the end of each question or part questions. For Examiner’s Use Section A B5 B6 B7 This document consist of 18 printed pages and NO blank page

2 © SRJC 2008 8872/02/Prelims/2008 [Turn Over 1 Iron tablets containing iron ( II) sulphate can be used to s upplement the daily iron intake in diet. The Health Sciences Au thority had regulated that all commercially available iron tablets must contain 15 to 18% by mass of iron. (a) Acidified potassium manganate (VII), KMnO4, which oxidises iron (II) sulphate, is used to estimate the amount of iron (II) ions, Fe2+, present in Brand A iron tablet. 2.00 g of the iron tablet was dissolved in dilute acid and the volume of the solution was made up to 100 cm3 in a volumetric flask. A 10.0 cm3 portion of this solution was titrated against 2.50 x 10 -4 mol dm-3 of potassium manganate (VII) solution. 13.50 cm 3 of the manganate (VII) solution was required to completely oxidise the Fe2+ present. (i) Write the overall equation of the reaction between MnO4 - and Fe2+. (ii) Calculate the concentration of Fe 2+ in the 100 cm3 solution. (iii) Hence, state with reasoning if the Brand A iron tablet meet s the regulation stated by the Health Sciences Authority. [4]

3 © SRJC 2008 8872/02/Prelims/2008 [Turn Over (b) Write the electronic configurations of Fe and Fe2+ ion. Fe: Fe 2+: [ 1 ] (c) On the diagram below, show and la bel clearly how the beams of the following particles are deflected when subjected to an electric field. (i) e l e c t r o n (ii) proton (iii) Fe atom You should relate clearly the magnitude and the direction of deflection of each beam to the other. (Any pencil markings will NOT be graded.) + - [3] [Total: 8]

4 © SRJC 2008 8872/02/Prelims/2008 [Turn Over 2 Styrene is an aromatic hydr ocarbon that is a precursor to polystyrene, an important synthetic material that is used in the maki ng of many substances such as plastic, rubber, insulation and fiberglass. The diagram below shows an energy cycle involving the compound styrene. CH CH 2 CH2CH3 8 CO2 5 H2O+ + H2 (g) styrene 1HΔ (l) (l) ) (2 21 2 g O+) (2 21 2 g O+ 43 ΔHΔH + 2HΔ (l)(g) (a) (i) Use the following data to calculate the standard enthalpy change of hydrogenation of styrene. o CHΔ hydrogen = –286 kJ mol -1 o CHΔ styrene = –4393 kJ mol -1 o CHΔ ethylbenzene = –4562 kJ mol -1 (ii) Calculate the amount of heat evolv ed when 1.000 g of styrene was burnt completely to heat up 200 cm 3 of water by 45.0 °C. Assume that the specific heat capacities of all solutions are 4.18 J g -1 K -1, and that all solutions have a density of 1.0 g cm-3.

5 © SRJC 2008 8872/02/Prelims/2008 [Turn Over (iii) Using the answer in (ii) , calculate the enthalpy change of combustion of styrene. (iv) Comment on the difference in values of standard enthalpy change of combustion of styrene in (i) and (iii). [4]

6 © SRJC 2008 8872/02/Prelims/2008 [Turn Over CH CH2 CHClCH3 + HCl (g) styrene (b) Given the following information, o fHΔ styrene = +104 kJ mol -1 o fHΔ hydrogen chloride = –92 kJ mol -1 o fHΔ (2-chloroethyl)benzene = –58 kJ mol -1 (l) (l) (i) Calculate the enthalpy change for the above reaction. (ii) The reaction above can be performed when ethylbenzene is treated with a small quantity of chlorine in t he presence of ultraviolet light. Both(1-chloroethyl)benzene and (2-chloroethyl)benzene are produced. Predict the approximate ratio in which they are formed. [2]

7 © SRJC 2008 8872/02/Prelims/2008 [Turn Over (c) A student accidentally poured some hot ac idified potassium manganate (VII) into a bottle of styrene, forming benzoic acid. In or der to salvage the styrene, he decided to adopt the following synthetic route. CO2H CH2OH CH2Cl CH2CN CH2CO2HCH2CH2OHCH CH 2 1 2 3 4 Suggest the correct reagents and conditions for the synthetic steps 1 to 5. Step 1 reagent(s): conditions: Step 2 reagent(s): conditions: Step 3 reagent(s): conditions: Step 4 reagent(s): conditions: Step 5 reagent(s): conditions: 5 [5]

8 © SRJC 2008 8872/02/Prelims/2008 [Turn Over (d) Complete the following table below: Number of carbon atom(s) Compound sp sp 2 sp 3 CH CH 2 CH2CH3 [1] [Total: 12]

9 © SRJC 2008 8872/02/Prelims/2008 [Turn Over 3 Because boron has one less electron than carbon, and nitrogen has one more, many B-N compounds are known as iso-electronic and iso-structural with their C-C analogues. Although the form er have similar shapes and boiling point, they are very different to the carbon compounds in their chemistry, mainly due to the electronegativity difference between the two elements. Compounds iso-electronic with saturat ed hydrocarbons, known as amino-boranes, may be prepared by the reaction of amines or ammonia with diborane, the simplest being the analogue of ethane (CH3CH3): B2H6(g) + 2NH3(g) 2BH3NH3(s) The two are very different physically. Ethane is gaseous at room temperature, having a boiling point of -89 oC, whereas the B-N com pound is solid at room temperature. However, the melting and boiling point of NH 3BH3 is undetermined because the compound decomposes before it melts. Several analogues of carboxylic acids are known, such as ammonia carboxyborane. NBH H H C H H OH O Some of these compounds display signifi cant physiological activity, including tumour inhibition and reduction of serum cholesterol in certain cases. Borazine, B 3N3H6, is iso-electronic and iso-struct ural with benzene, but the two compounds have little chemical resemblance. The former does not have the same delocalized π electron structure as benzene, since the π electrons are concentrated on the nitrogen atoms, and hence it can be regarded as having three electron-rich, reactive double bonds. Unlike benzene, borazine undergoes electrophilic addition readily. For example, 1 mol of borazine reacts with 3 mol of HC l to form a compound which is analogous to 1,3,5-trichlorocyclohexane. Many symmetrically tri-substituted der ivatives of borazine have been prepared. The fo