JJC_H2 Chemistry 9746 Prelim P3 Question paper

JURONG JUNIOR COLLEGE PRELIMINARY EXAMINATION 2008 H2 CHEMISTRY PAPER 3 9746 / 3 Monday 18 th August 2008 2 hours INSTRUCTIONS TO CANDIDATES Do not open this question booklet until you are told to do so. Write your name and class in the spaces provided on the cover sheet and writing papers provided. Write in dark blue or black pen. You may use a pencil for any diagrams, graphs, or rough working. Do not use highlighters or correction fluid. Answer any four questions. Begin your answer to each new question on a fresh sheet of writing paper. At the end of the examination, arrange the answers in numerical order and attach the cover sheet on top. INFORMATION FOR CANDIDATES A Data Booklet is provided. Do not write anything on the Data Booklet. You are reminded of the need for good Englis h and clear presentation in your answers. You are advised to show all workings in calculations. The number of marks is giv en in brackets [ ] at the end of each question or part question. ___________________________________________________________________________________ _ This question booklet consists of 11 printed pages, including this page.

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Answer any four questions. 1. Sulfuric acid, H2SO4, is a strong mineral acid wh ich is an important chemical used in the manufacture of phosphate fe rtilisers. It is also used as an oxidising agent to remove rust in the iron and steel-making industry. (a) The manufacture of sulfuric acid in volves the reaction between sulfur dioxide and oxygen. 2SO2(g) + O2(g) = 2SO3(g) ΔH = −197 kJ mol−1 The reaction is carried out at a temperature of 450 °C in the presence of a catalyst. (i) Explain why a temperature of 450 °C is usually employed for the reaction. (ii) When a 2:1 ratio of SO 2 and O2 at a total initial pressure of 3 atm is passed over a catalyst at 450 °C, the percentage conversion of SO2 into SO3 was found to be 98 %. Calculate the equilibrium partial pressures of SO 2 and O 2 and hence find the value for Kp. (iii) State and explain the effect on Kp and the percentage conversion of SO 2 into SO 3 when the volume of the reaction vessel is reduced. [6] (b) SO2, the key reactant for the manufacture of sulfuric acid, is an oxide of a Period 3 element. The table below shows the melting points of SO 2 and oxides of other Period 3 elements. Compound Formula eltM ing point / °C sodiu Na2O 1132 m oxide alum l2O 2980inium oxide A 3 sulfu SO2 −70 r dioxide (i) Briefly relate the melting points of these oxides to their structure and bonding. (ii) Describe the reactions, if any, of each of these oxides with water, stating the approximate pH of any solution formed, and writing a balanced equation for any reaction that takes place. [6] Page 3 of 11

1. (c) Concentrated sulfuric acid is also an important reagent in many organic reactions where it can p