HCI Prelim C2_P3

This document consists of 12 printed pages. HWA CHONG INSTITUTION C2 Preliminary Examinations Higher 2 CANDIDATE NAME CT GROUP 16S CENTRE NUMBER INDEX NUMBER CHEMISTRY Paper 3 Free Response Candidates answer on separate paper. Additional Materials: Answer Paper Data Booklet 9729/03 18 September 2017 2 hours READ THESE INSTRUCTIONS FIRST Write your name, CT group, centre number and index number clearly in the spaces above. Write in dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions. Section B Answer one question. Begin each question on a new sheet of writing paper. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. 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. Circle the question numbers for the questions that you have attempted on the cover page provided.

2 © Hwa Chong Institution 2017 9729 / 03 / C2 Prelim 2017 Section A Answer all the questions in this section. 1 (a) Azurite is a deep blue copper-containing mineral. For many centuries, finely ground rock containing azurite has been used as a pigment in blue paints. Azurite is a mixture of copper(II) carbonate and copper( II) hydroxide. The formula of pure azurite is Cu 3(CO3)2(OH)2, which has a relative formula mass of 344.5. The percentage by mass of pure azurite in a sample of finely ground rock can be determined by back titration. 3.70 g of the sample is added to 100 cm 3 of 0.425 mol dm–3 sulfuric acid. The resulting solution was made up to 250 cm3 with distilled water. 25.0 cm 3 of the diluted solution required 26.50 cm 3 of 0.100 mol dm –3 sodium hydroxide for neutralization. Dilute sulfuric acid reacts with pure azurite as shown in the following equation. Cu 3(CO3)2(OH)2(s) + 3H2SO4(aq)  3CuSO4(aq) + 4H2O(l) + 2CO2(g) Calculate the percentage by mass of pure azurite in the sample. You may assume that azurite is the only substance in the rock that reacts with sulfuric acid. [3] (b) The brick-red precipitate, Cu 2O, dissolves in concentrated ammonia solution to form a colourless complex ion P, [Cu(NH3)x]n+, which has a linear geometry about the central metal ion. When left exposed to air, the colourless complex ion P turns into a deep blue solution, containing the complex ion [Cu(NH3)4]2+. (i) State the value of x and write the formula of complex ion P. [2] (ii) With the help of the Data Booklet , write the two half equations, and hence the overall equation for the reaction of