MI_2008_PU2_ Promotional_H1Chem P2_ans

Class Adm No Candidate Name: _______________________ Promotional Examinations 2008 Pre-university 2 CHEMISTRY HIGHER 1 8872/2 Monday 8th Sept 2008 2 hours Additional materials: Answer paper Data Booklet 5 pieces of foolscap paper Cover page READ THESE INSTRUCTIONS FIRST Do not open this booklet until you are told to do so. Write your name, index number 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. Section A Answer all questions. Section B Answer any two questions on the writing papers. At the end of the examination, hand in your answers to Section A and Section B separately. The number of marks is given in brackets[ ] at the end of each question or part question. For Examiner's Use Section A B5 B6 B7 Total This question paper consists of 16 printed pages.

Section A: Structured Questions (40m) Answer ALL questions in the spaces provided. 1. Acidified KMnO 4, which oxidizes iron(II) compounds, is used to estimate the amount of iron present in substances such as flour. 1.00g of flour was shaken vigorously with dilute H2SO4 and the volume of the solution was made up to 100cm3 in a volumetric flask. A 10.0cm3 portion of this solution was titrated against 5.00x10 -6 moldm-3 of KMnO4 solution. 11.00cm3 of the KMnO 4 solution was required to completely oxidized the iron(II) salt to iron(III) salt. (i) Write a balanced equation to show the above reaction. [2] Fe2+ Æ Fe3+ +e MnO4 - + 8H+ +5e Æ Mn2+ + 4H2O Overall equation : 5Fe2+ + MnO4 - + 8H+ Æ 5Fe3+ + Mn2+ + 4H2O ; ecf given (ii) Calculate the concentration of Fe2+ in the flour solution. [2] No. of mol MnO4 - = 5.00x10-6 x 0.011 = 5.50x10-8 No. of mol Fe2+ in 10.0cm3 = 5.50x10-8 x 5 = 2.75x10 -7 ; ecf given No. of mol of Fe2+ in 100cm3 = 2.75x10-7 x 10 = 2.75x10-6 Concentration of Fe2+ = 2.75x10-6 x (1000/100) = 2.75x10-5 moldm-3 ; ecf given [Turn over 2 (iii) Hence, determine with calculation, if this flour meets the requirement of containing 16.5mg of iron per 100g of flour by law. [2] 16.5mg = 1.65 x 10-2g Mass of Fe in 1.00g of flour = 2.75x10-6 x 55.8 = 1.535 x 10-4g Mass of Fe in 100g of flour = 1.535 x 10-4 x 100 = 1.535 x 10-2 g ; The flour does not meet the requirement. ; 2 half-equation 1m marks given only with calculation [Total marks: 6m]

2. Sulphur and its isotopes are mainly used in medical applications. Sulphur also known as brimstone has been used for thousands of years to cure skin ailments. Ancient cultures relied on sulphur to treat a variety of illnesses as well as to make dyes and