MI_2008_PU2_ Promotional_H1Chem P2_Qn

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. Attach the cover page to your answer scripts for section B. The number of marks is given in brackets[ ] at the end of each question or part question. This question paper consists of 17 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] ……………………………………………………………………………………………… ………………………………………………………………………………………………. (ii) Calculate the concentration of Fe2+ in the flour solution. [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] [Total marks: 6m] [Turn over 2

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 other useful products. (a) The relative isotopic mass and percentage abundances of the isotopes of a sample of sulphur are shown in the table. relative isotopic mass % abundance 32S 94.93 34S 5.07 Calculate the relative atomic mass for sulphur in the sample. [1] (b) Oxides of sulphur contribute towards air pollution. Draw a dot and cross diagram to show the bonding in a molecule of sulphur trioxide, SO 3. Hence state the shape and bond angle of SO3 [ 3 ] (c) The melting points of silicon dioxide and sulphur trioxide are shown as follows: compound melting point / oC SiO2 2830 SO3 17 Briefly relate these melting points to the structure and bonding in each of these