NYJC_Prelim_CHEM_P3 ANS

NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY 9746/03 Paper 3 16 September 2009 2 hours Candidates answer on writing paper Additional Materials: Data Booklet Graph paper READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the 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 4 out of 5 questions. Write your answers on the writing paper provided Begin each question on a fresh piece of paper. You are advised to show all working and calculations This document consists of 9 printed pages and 1 blank page

2 H2 Chemistry 9746/03/NYJC J2/09PX 1(a) (i) Element A The sharp drop in value from G to H i ndicates that G is from Group I where the second ionization energy involves t he removal of an electron from the inner shell . Hence Element A is in Group III and is Aluminium. [2] (b) (i) AB(CO3)2 → AO + BO + 2 CO2 [1] (ii) Assume : AB(CO3)2 → AO (s) + BO (aq) + 2 CO2 Masses given : 0.400 0.057 (0.275 – 0.057) x Therefore, x = 0.400 – 0.275 = 0.125 g [1] (iii) Soln : Let Ar of A be a and that of B be b AB(CO3)2 → AO (s) + BO (aq) + 2 CO2 Mass / g : 0.400 0.057 0.218 0.125 Determining amts and using mol ratios Amt of CO2 = 0.125/44 = 0.00284 mol Amt of AO = 0.057/(a + 16) = 0.00284 /2 mol Giving a = 24.1, Therefore A is Mg Amt of BO = 0.218/(b + 16) = 0.00284 /2 mol Giving b = 137.5, Therefore B is Ba (c) MgO > NaF > H2O > CH3NH2 > CO2  CO 2 have simple molecular structure consisting of CO2 molecules held together by van der waals forces.  CH 3NH2 and H2O have simple molecular structures consisting of CH3NH2 and H2O molecules held together by stronger hydrogen bonds.  H 2O has 2 lone pair hydrogen units while CH3NH2 has 1 thus H2O has higher boiling point.  NaF and MgO have ionic structures consis ting of oppositely charged ions held together by strong electrostatic forces. MgO has higher boiling point because it has higher ionic charges than NaF. [5]

3 H2 Chemistry 9746/03/NYJC J2/09PX (d) (i) For the amino acid resi due to be found on the outer surface of a water soluble globular protein, the R group must be a hydrophilic group.  Hence, Serine (ser) will be found on the outer surface The OH group on serine can form hydrogen bonds with water hence soluble.  Lysine (Lys) will also be found on the outer surface The NH2 group on lysine can form hydrogen bonds with water hence making it soluble. [2] (ii) For Phe, Pro, Leu : Hydrophobic or van der Wa