NYJC_H1 Chem Prelim 08 P2_Answers

NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAM Higher 1 CANDIDATE NAME CLASS TUTOR’S NAME CHEMISTRY 8872/02 Paper 2 10 Sep 2008 Candidates answer Section A on the Question Paper. 2 hours Candidates answer Section A on the Question Paper Additional Materials: Answer Paper Data Booklet 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. For Examiner’s Use A1 A2 A3 A4 B1 B2 B3 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. Total This document consists of 15 printed pages. [Turn over

2 For examiner’s use only Section A Answer all questions in this section in the spaces provided. 1 The rate of hydrolysis of a chloroalkane, RC l with aqueous sodium hydroxide depends on the concentration of the r eactants at a fixed temperature T1. The values for the initial rates of hydrolysis at various initial concentrations have been determined. These are shown in the table below. Expt Initial conc. of NaOH / mol dm-3 Initial conc. of RCl / mol dm-3 Initial rate / mol dm-3 s-1 1 0.0200 0.0150 4.0 x 10-4 2 0.0200 0.0225 6.0 x 10-4 3 0.0300 0.0225 9.0 x 10-4 4 0.0600 0.0300 x (a) Deduce the orders of reaction with respect to each of the reactants. Hence, write the rate equation for the hydrolysis of the chloroalkane. [3] Orders wrt NaOH = 1 Orders wrt RCl = 1 Rate = k [NaOH][RCl] (b) Based on your answer above, calculate the magnitude of x. [1] x = (3 x 2 x 4.0 x 10 -4) = 2.4 x 10 -3 mol dm-3 s-1

3 (c) Describe and explain, with an appropriate diagram, how t he rate of this reaction is affected when the experiment is repeated at a higher temperature, T2. [3] For examiner’s use only No. of molecules Correct Boltzmann distribution with legend. As T increases, proportion of molecules with E > Ea increase. Frequency of activated collision increases. Rate increases. [Total: 7 marks] 2 Nitrogen and phosphorous ar e in the same group in the Periodic Table. The information in the following table is provided for compounds of nitrogen and phosphorous. Compound M r Boiling point / K NH3 17.0 240 PH3 34.0 185 (a) Briefly explain the difference in boiling points of NH 3 and PH3. [2] More energy is needed to break the relatively strong hydrogen bonds between the NH 3 molecules than the weak van der Waals’ forces of attrac