NJC H2 Chem 2012 Prelim P2 QP

CANDIDATE NAME SUBJECT CLASS NATIONAL JUNIOR COLLEGE PRELIMINARY EXAMINATIONS Higher 2 REGISTRATION NUMBER CHEMISTRY 9647/02 Paper 2 Structured Fri 14 Sept 2012 Answer on the Question Paper. 2 hours Additional Materials: Data Booklet READ THE INSTRUCTIONS FIRST For Examiner’s Use Write your subject class, registration number and 1 /12 name on all the work you hand in. 2 /10Write in dark blue or black ink in the spaces provided. You may use a soft pencil for any diagrams, graphs 3 /18or rough working. Do not use paper clips, highlighters, glue or correction fluid. 4 /11 Answers all questions. 5 /6 6 /15 The number of marks is given in brackets [ ] at the Total /72end of each question or part question. This document consists of 17 printed pages and 1 blank page.

NJC/H2 Chem/02/2012 [Turn over 2 1 Planning (P) The hydroxides of Group I metals (LiOH, NaOH, KOH, RbOH, CsOH) are highly corrosive white solids which rapidly absorb water vapour on exposure to the atmosphere. All of these solids dissolve exothermically in water. The enthalpy change of solution, Δ H soln, is the energy change associated with the following reaction. MOH(s) + (aq) ® M+(aq) + OH–(aq) where M represents the Group I metal. Both lattice energy and hydration enthalpy play an important part in determining the magnitude of ΔHsoln. Lattice energy and hydration enthalpy are both more exothermic when ions carry higher charges and/or ions have smaller radii. When comparing Group I hydroxides, changes in Δ Hhydration are more significant than changes in lattice energy. (a) Sketch the likely trend in ΔHsoln from LiOH to CsOH and explain your answer. Explanation: …………………………………………………………………………………….….…………….. ..……….……………………………………………………………………………….….……….. . ………………….…………………………………………………………………….….……….. [2] For Examiner’s Use ΔHsoln LiOH NaOH KOH RbOH CsOH 0

NJC/H2 Chem/02/2012 [Turn over 3 (b) Without considering heat loss , based on the information given, identify one possible source of error in the experiment to determine Δ Hsoln of the hydroxides of Group I metals. State how you would minimise the effect of this source of error. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. [1] (c) Identify a safety risk in the experiment and suggest how you would minimise it when carrying out the experiment. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. [1] (d) Given the enthalpy change of solution of lithium hydroxide is approximately -21 kJ mol -1, describe the procedure you would carry out to find its enthalpy change of solution. Your plan should give a step-by -step description of the method, including appropriate masses and volumes of reagents. You may use the apparatus normally found in a school or college laboratory. The following data may be of use in planning the details of your experiment. Ar: Li, 6.9; O, 16.0; H, 1.0 4.3 J are required to raise the temperature of 1.0 cm 3 of any solution by 1°C. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. For Examiner’s Use

NJC/H2 Chem/02/2012 [Turn over 4 ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. [4] (e) A student was interested to investigate how the enthalpy change of neutralisation, DHneutralisation, varies when acids such as hydrochloric acid, HC l and ethanedioic acid, (CO2H)2 are neutralised with aqueous solutions of a Gro