SRJC_2008 JC2 Prelims H1 Paper 2 Solutions

1 SERANGOON JUNIOR COLLEGE General Certificate of Education Advanced Level Higher 1 CHEMISTRY 8872/02 Preliminary Examination Paper 2 SOLUTIONS 1 Iron tablets containing iron ( II) sulphate can be used to supplement the daily iron intake in diet. The Health Sciences Authority had r egulated that all commercially available iron tablets must contain 15 to 18% by mass of iron. (a) Acidified potassium manganate (VII), KMnO 4, which oxidises iron (II) sulphate, is used to estimate the amount of iron (II) ions, Fe 2+, 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 cm 3 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+. Oxidation: Fe2+ Fe3+ + e Reduction: MnO4 - + 8H+ + 5e Mn2+ + 4H2O 5Fe 2+(aq) + MnO4 -(aq) + 8H+(aq) Æ 5Fe3+(aq)+ Mn2+(aq) + 4H2O (l) (ii) Calculate the concentration of Fe2+ in the 100 cm3 solution. amount of MnO4 - in 13.50 cm3 = 410 x 5 . 2 x1000 5 . 13 − = 3.370 x 10-6 mol from (3) mole ratio: 5Fe2+ ≡ MnO4 - amount of Fe2+ in 10 cm3 = 3.37 x 10-6 x 5 = 1.6875 x 10-5 mol amount of Fe 2+ in 100 cm3 = 1.6875 x 10-5 x 10 = 1.6875 x 10-4 mol concentration of Fe 2+ in 100 cm3 solution = 1.6875 x 10-4 / 0.1 = 1.69 x 10 -3 mol dm-3 (iii) Hence, state with reasoning if the Brand A iron tablet meet s the regulation stated by the Health Sciences Authority. Mass of Fe 2+ present in 2g of tablet A = 1.6875 x 10-4 x 55.8 = 9.4163 x 10 -3 g Percentage of Fe present in tablet A = (9.4163 x 10 -3 / 2) x 100 % = 0.471 % No , the iron tablet does no meet the requirement of HSA as its iron content is not within the range 15 to 18% by mass.

2 (b) Write the electronic configurations of Fe and Fe2+ ion. Fe atom: 1s22s22p63s23p63d64s2 F e 2+ ion: 1s22s22p63s23p63d6 (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.) Fe atom + - Electron / e Proton / p [Total: 8 m]

3 CH CH 2 2 Styrene is an aromatic hydr ocarbon tha