IJC_H1_CHEM_P2_solution

INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION 2 in preparation for General Certificate of Education Advanced Level Higher 1 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY Paper 2 Structured and Free Response Questions Section A: Structured Candidates answer Section A on the Question Paper Section B: Free Response Additional Materials: Writing Paper Data Booklet 8872/02 2 Sept 2015 2 hours READ THESE INSTRUCTIONS FIRST Write your index number, name and civics group on all the work you hand in. Write in dark blue or black pen. You may use pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A: Structured Questions (40m) Answer all questions in the space provided. Section B: Free Response Questions (40m) Answer two questions on separate writing papers. You are advised to show all working in calculations. You are reminded of the need for good English and clear presentation in your answers. You are reminded of the need for good handwriting. Your final answers should be in 3 significant figures. You may use a calculator. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 13 printed pages and 1 blank page. Innova Junior College [Turn over For Examiner’s Use Section A 1 12 2 8 3 10 4 10 Section B 20 20 Significant figures Handwriting Total 80

2  IJC 2015 Prelim 2/8872/02 [Turn over For Examiner’s Use Section A Answer ALL questions on the spaces provided. 1 Chromium is a transition metal. Chromium compounds are highly valued as pigments for their vivid green, yellow, red and orange colours. (a) The element chromium has four main naturally occurring isotopes. isotope relative abundance / % 50Cr 4.33 52Cr 83.8 53Cr 9.50 54Cr 2.37 Use the relative abundance data to calculate the relative atomic mass of Cr, showing your working clearly. A r = 2.389.5083.74.35 54(2.38)53(9.5)52(83.7)50(4.35)   = 52.0 [1] (b) Chromium(III) chloride dissolves in water to form a green solution. Draw a labelled diagram to illustrate the interaction between a Cr3+ ion and a water molecule. [2] (c) Chromium(IV) oxide, CrO 2 is a black solid that disproportionates into a mixture of Cr3+ and Cr2O7 2– in acidic solutions. The half equation for the reduction of CrO 2 to Cr3+ is as follows: CrO2 + 4H+ + e Cr3+ + 2H2O To determine the percentage purity of a sample of chromium( IV) oxide, a student dissolves 1.5 g of impure sample in 20 cm 3 of sulfuric acid and make up the total volume to 100 cm 3 with disti