NJC_H2_CHEM_P3_Solutions Prelim

1 [Turn Over NATIONAL JUNIOR COLLEGE PRELIMINARY EXAMINATIONS Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 3 Free response 9647/03 Wed 17 Sep 2014 2 hours READ THESE INSTRUCTIONS FIRST Answer any four questions. Start your answer to each question on a fresh piece of paper. A Data Booklet is provided. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely behind the cover page. This paper consists of 11 printed pages and 1 cover page.

2 [Turn Over 1 Iodine monochloride, ICl, is an interhalogen compound that is formed when chlorine gas is passed through iodine crystals. Generally, interhalogen compounds have chemical properties similar to that of halogens. (a) (i) Predict the physical state of ICl at room temperature. Liquid / solid. Mr of ICl : 162.5 Mr of Br2 : 159.8 Strength of td-id expected to be similar to that of Br2, hence liquid state. Td-id stronger than Cl2 but weaker than I2. (ii) By considering the partial charges in ICl, explain how water reacts with ICl. The lone pair of electrons on the oxygen of H2O attacks the + I, breaking the I-Cl bond, forming HOI. The H+ then combines with the Cl¯. (iii) Hence construct an equation for the reaction of ICl with water. ICl + H2O  HOI + HCl [3] (b) Methylbenzene reacts with ICl in the presence of FeCl3 to form compound A. (i) Draw the structure of A. 2-iodo methylbenzene (ii) Describe the mechanism of this reaction, clearly indicating the role of FeCl3. Electrophilic substitution reaction FeCl3 + ICl  [FeCl4]¯ + I+ H+ + [FeCl4]¯  FeCl3 + HCl [4]

3 [Turn Over (c) FeCl3 and FeF3 are both formed from a metal and a non -metal. However, in molten state, only FeF3 is able to conduct electricity and FeCl3 does not. (i) Suggest the structures of FeC l3 and FeF 3 and explain why iron forms two different types of compounds when reacted with the different hal ogens – fluorine and chlorine. FeCl3 : Simple covalent molecules FeF3 : Ionic lattice structure Fe3+ has a high charge density and is hence able to polarise the larger electron cloud of the chlorine atoms resulting in more extensive sharing of electrons hence forming a covalent bond. Fluoride ions due to their small size have low polarisability. (ii) Using the information given below as well as relevant data from the Data Booklet, construct an energy level diagram for the formation of FeF 3 from its elements to determine its lattice energy. enthalpy change of atomisation of Fe +340 kJ mol–1 first electron affinity of F –328 kJ mol–1 standard enthalpy change of formation of FeF3 –989 kJ mol–1