NJC Prelims Paper 1_Answers Final

NJC/H2 Chem Preliminary Examination/02/2021 1 [Turn over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 1 Multiple Choice Additional Materials: Optical Answer Sheet Data Booklet 9729/01 15 September 2021 1 hour READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, highlighters, glue or correction fluid. Write your name, subject class and registration number on the Answer Sheet in the spaces provided unless this has been done for you. There are thirty questions on this paper. Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the separate Answer Sheet. Read the instructions on the Answer Sheet very carefully. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet. The use of an approved scientific calculator is expected, where appropriate. Instructions on how to fill in the Optical Mark Sheet Shade the index number in a 5 digit format on the optical mark sheet: 1st digit and the last 4 digits of the Registration Number. Example: Student Examples of Registration No. Shade: 2005648 25648 This document consists of 12 printed pages.

NJC/H2 Chem Preliminary Examination/02/2021 2 Answer keys for 2021 SH2 H2 Chemistry Prelim Paper 1 1 C 11 A 21 B 2 A 12 A 22 C 3 C 13 A 23 D 4 C 14 A 24 D 5 A 15 C 25 C 6 D 16 C 26 B 7 C 17 D 27 D 8 D 18 C 28 A 9 C 19 C 29 B 10 C 20 C 30 B 1 A sample of element sulfur contains four isotopes of the following composition. relative isotopic mass relative abundance 32 95.02 33 0.76 34 4.20 36 0.02 What is the relative atomic mass of sulfur in this sample? A 32.07 B 32.08 C 32.09 D 32.10 Ans : C Ar = ( ଽହ.଴ଶ ଵ଴଴ × 32 ) + ( ଴.଻଺ ଵ଴଴ × 33 ) + ( ସ.ଶ ଵ଴଴ × 34 ) + ( ଴.଴ଶ ଵ଴଴ × 36 ) = 32.0924 | 32.09 2 When 15 cm3 of a gaseous organic compound were completely burnt in an excess of oxygen, 30 cm3 of carbon dioxide and 15 cm3 of nitrogen were formed, all volumes being measured at the same temperature and pressure. Which could be the formula of the organic compound? A C2H4N2 B C2H7NO C C3H7NO D C3H6N2 Ans : A According to the question, all the carbon atoms in the organic compound are converted into CO2 when burnt completely in excess O2, and the nitrogen atoms are converted into N2. Assuming that the formula of the organic compound is CxHyNz, when one mole of CxHyNz undergoes combustion, x moles of CO2 will be produced and z/2 moles of N2 will be produced. The volume ratio of organic compound : CO2 : N2 = 15 cm3 : 30 cm3 : 15 cm3 Mol ratio = 1 : 2 : 1 Hence x = 2 and z = 2 which fits the molecular formula C2H4N2.

NJC/H2 Chem Prelimin