TJC_08 TJC H1 Prelim Paper 2 Questions

T CANDIDATE NAME CIVICS GROUP / CHEMISTRY 8872/02 Paper 2 17th September 2008 2 hours Candidates answer Section A on the Question Paper. Additional Materials: Answer Paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your Civics Group number and candidate name on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer two questions on separate answer paper. 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 15 printed pages. For Examiner’s Use Paper 1 /30 Paper 2 A1 /10 A2 /8 A3 /11 A4 /11 B /20 B /20 Total /110 Percentage % TEMASEK JUNIOR COLLEGE Preliminary Examinations Higher 1

For Examiner’s Use 2 Section A Answer all questions in this section in the spaces provided. 1 (a) For decades, scientists were puzzled by why dinosaurs suddenly became extinct 65 million years ago. In studying core samples of rock dating back to that period, scientists found an unusual high level of iridium. This possibly came from an iridium-rich asteroid that struck the Earth’s surface and the mystery to dinosaurs’ extinction was solved. Iridium exists as two naturally occurring isotopes, iridium-191 and iridium-193. (i) Define the term relative atomic mass. ........................................................................................................................................... ........................................................................................................................................... (ii) The relative atomic mass of iridium is 192.2. Calculate the natural abundance, in percentage, of each isotope. (iii) Iridium is one of the rarest metals in the Earth’s crust. It is thought to exist in 2 parts per billion (ppb). Calculate the mass of iridium in 10 tonnes of Earth’s crust. [1 billion = 10 9, 1 tonne = 1000 kg] [4] TJC 2008 8872/02/PRELIM 2008