MJC_H2_CHEM_P2 ANS Prelim

Reg NumberClass Candidate Name _____________________________ Meridian Junior College 2009 JC 2 Preliminary Examination Answers H2 Chemistry 9746 22 September 2009 1 hr 30 min No part of this paper should be repro duced for commercial use without the prior written permission of Meridian Junior College. Paper 2 STRUCTURED QUESTIONS Additional Materials Data Booklet INSTRUCTION TO CANDIDATES Write your name, class and register number in the spaces provided at the top of this page. Write in dark blue or black ink. You may use a soft pencil for any diagrams or graphs. You are reminded on the need for good English and clear presentation of your answers. INFORMATION FOR CANDIDATES FOR EXAMINER’S USE The number of marks is given in brackets [ ] at the Q1 / 8end of each question or part of question. Q2 / 8 Q3 / 11 Q4 / 11 Q5 / 12 Q6 / 10 Total / 60 This question paper consists of 17 printed pages 1

Answer all the questions in the space pro vided 1 Early Periodic Tables, such as that devised by Mendeleev, listed the then known elements in order of their relative atomic mass. (a) (i) When Mendeleev created the table, t here were uncertainties regarding the relative atomic mass of telluri um. It is now known that there are eight isotopes of tellurium. Comple te the following table and use it to calculate the relative at omic mass of tellurium. isotope percentage abundance isotopic mass x percentage abundance tellurium-120 0.09 11 tellurium-122 2.46 300 tellurium-123 0.87 107 tellurium-124 4.61 572 tellurium-125 6.99 874 tellurium-126 18.71 2357 tellurium-128 31.79 4069.12 tellurium-130 34.48 4482.40 Complete the above table and give your answers to two decimal places. Hence, calculate the relative atomic mass of tellurium to five significant figures. Ar of Te = (11 + 300 + 107 + 572 + 874 + 2357 + 4069.12 + 4482.40) 100 = 127.73 2

(ii) TeO2 resembles aluminium oxide in its acid-base properties. TeO 2, SiO2 and P 4O10 cannot be distinguished based on their physical appearance. If a sample of one of the oxides was provided as a fine powder, describe the reactions you could ca rry out on the powder to determine which of the three oxides it was. In clude all relevant equations in your answer. Dissolve a portion of the sample in water. If the oxide is soluble in water, then the oxide is P4O10 P 4O10 + 6H2O 4H3PO4 Dissolve another sample of the oxide in HCl(aq). If the oxide is soluble in HC l, then the oxide is TeO 2 The oxide that is insoluble in HC l is then SiO2 TeO2 + 4 HCl  TeCl4 + 2H2O . [5] (b) Another chemist looking for patterns in the propert