RVHS H2 Chem 2012 Prelim P3 QP

CANDIDATE NAME CLASS CENTRE NUMBER RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION 6 S INDEX NUMBER H2 CHEMISTRY 9647/03 Paper 3 Free Response 18 September 2012 2 hours Candidates answer on separate paper. Additional Materials:Answer Paper Cover Page Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class, centre number and index number on all the work you hand in. Write in dark blue or black pen on both sides of paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any four questions. Begin each question on a fresh sheet of paper. A Data Booklet is provided. Do not write anything on it. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together, with the cover page on top. _______________________________________________________________________________ This document consists of 11 printed pages and 1 blank page. River Valley High School 9647/03/PRELIM/12 [Turn over Preliminary Examination 2012

2 River Valley High School 9647/03/PRELIM/12 [Turn over Preliminary Examination 2012 Answer any four questions. 1 (a) One common characteristic of transition elements is the ability to form complexes. Transition elements react with carbon monoxide to form a class of complexes known as metal carbonyls. One aspect of metal carbonyls that is unusual for metallic compounds is that they are often volatile. N ickel carbonyl was first synthesised in 1890 by Ludwig Mond by passing carbon monoxide over nickel metal. Nickel carbonyl has a boiling point of 43 °C and is extremely poisonous. (i) Draw the ‘dot-and-cross’ diagram of carbon monoxide. (ii) Explain in terms of structure and bonding why nickel carbonyl has a low boiling point. (iii) A 2.00 g sample of nickel carbonyl was vaporised and found to occupy a volume of 314 cm 3 at 50 °C and 1 atmosphere pressure. Determine the Mr of nickel carbonyl. (iv) Nickel carbonyl has the general formula Ni(CO) x. Using the answer in (iii) , determine the coordination number of nickel in nickel carbonyl and suggest the shape of the complex. [7] (b) Transition metal compounds are often coloured. (i) Explain why transition metal compounds are often coloured. (ii) When a solution of dilute sulfuric acid was electrolysed using copper electrodes, a blue solution was obtained. On heating this solution to dryness, an anhydrous white solid was eventually obtained. When concentrated hydrochloric acid was electrolysed using copper electrodes in a separate experiment , a yellow solution was obtained. On adding water, the colour of the solution turned from yellow to green and eventually blue. Explain these observations. State clearly the formula of any coloured species. [9]