2013 MJC H1 Chemistry P2 QP

©MJC Chemistry Name: ___________________ Class: ________ Reg Number: _____ MERIDIAN JUNIOR COLLEGE JC2 Preliminary Examination Higher 1 _____________________________________________________________________ Chemistry 8872/02 Paper 2 17 September 2013 2 hours Additional Materials: Data Booklet Writing Papers _____________________________________________________________________ READ THESE INSTRUCTIONS FIRST Write your name, class and register number in the spaces at the top of this page. This booklet contains Section A and Section B. Section A : Pg 2 to 13 Answer all questions in Section A in the spaces provided on the question paper. You are advised to spend about 1 h on Section A. Section B : Pg 14 to 20 Answer 2 out of 3 questions in Section B. You are advised to spend about 1 h on Section B. Hand in Section B separately from Section A. Fasten your answers for Section B behind the given Cover Page. Detach the Cover Page from the last page behind this booklet. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. _____________________________________________________________________ This document consists of 20 printed pages (including this cover page) Examiner’s Use Paper 1 MCQ / 30 m / 33 % Paper 2 Section A Q1 / 12 m Q2 / 17 m Q3 / 11 m Paper 2 Section B / 40 m Paper 2 Total / 80 m / 67 % Grand Total / 100 % Grade

2 [Turn Over Section A : Structured Questions Answer all the questions in this section in the spaces provided. 1 An early Periodic Table devised by Mendeleev listed the elements known then in order of their relative atomic mass. (a) (i) When Mendeleev created the table, there were uncertainties regarding the relative atomic mass of tellurium. It is now known that there are eight isotopes of tellurium. Complete the following table. Give your answers to four significant figures. isotope percentage abundance isotopic mass x percentage abundance tellurium-120 0.09 11.00 tellurium-122 2.46 300.0 tellurium-123 0.87 107.0 tellurium-124 4.61 572.0 tellurium-125 6.99 874.0 tellurium-126 18.71 2357 tellurium-128 31.79 tellurium-130 Hence, calculate the relative atomic mass of tellurium to 1 decimal place.

3 [Turn Over (ii) The electronic configuration of tellurium and antimony are as follows: Te: [Kr]5s25p4 Sb: [Kr]5s25p3 Explain why the first ionisation energy of tellurium is lower than that of antimony. ……………………………………………………………………………………..… ………………………………………………………………………………..……… ………………………………………………………………………………….…[4] (b) Tellurium (IV) chloride, TeCl4, exists as a vapour at 380°C. Gaseous TeC l4 has a structure similar to sulfur tetrafluoride, SF4. (i) Draw a dot-and-cross diagram of TeCl4. (ii) Predict, with reasoning, the shape of TeCl4. ………………………………………………………………………………..……… ………………………………………………………………………………..……… ……………………………………………………………………………………..… ……………………………………………………………………………………..… ………………………………………………………………………………..……… (iii) The compound TeCl4 exists, but OCl4 does not. By considering the possible types of bonding in the two compounds, suggest a reason for this difference. (Assume that Te and O atoms occupy a central position in each of these molecules.) ………………………………………………………………………………..……… …………………………………………………………………………..…………… …………………………………………………………………………….………[4]

4 [Turn Over (c) Tellurium resembles silicon in many aspects. For example, both are metalloids and are used as semiconductors. Tellurium ( IV) chloride, TeC l4, dissolves in water in the same way as silicon (IV) chloride, SiCl4. Describe the reaction, if any, of the chlorides of aluminium and tellurium with water. Give equations for any reactions and suggest the pH values of the resulting solution. …………………………………………………………………………………..…………… ……………………………………………………………………………………………..… …………………………………………………………………………………..…………… ……………………………………………………………………………………………..… …………………………………………………………………………………..…………… ……………………………………………………………………………………………..… …………………………………………………………………………………..…………… ……………………………………………………………………………………………..… …………………………………………………………………………………..…………… ……………………………………………………………………………………………..… …………………………………………………………………………………..…………… …………………………………………………………………………………………….[4] [Total : 12]

5 [Turn Over 2 Steel is an interstitial alloy, as carbon atoms fit in between iron atoms in the lattice. Brass is a substitution alloy, as zinc atoms replace the copper ato ms in the lattice. Stainless steel is a combination of interstitial and substitution alloys, because carbon atoms fit into the interstices, but some of the iron ato ms are replaced with nickel atoms. The alloy’s structure will determine properties such as hardness, which measures the material’s resistance to permanent shape change when a force is applied. These properties rely on how much electrostatic attraction is present between ions and electrons in any given volume of the lattice. Lattice Strength  q r   (a) The ionic radius and ionic charge of the f ollowing element are given in the following table. Element C V Cr Fe Ni Cu Zn W Ionic radius (10-12 m) 16 64 62 64 60 73 74 66 Ionic charge +4 +3 +3 +3 +3 +2 +2 +4 (i) Adding a small amount of which metallic element is likely to increase the lattice strength of iron most? Give a reason for your answer. …………………………………………………………………………………......… ……………………………………………………………………………………..… (ii) From the table above, suggest another element that can be added to iron to form a substitution alloy. …………………………………………………………………………………….[2] (b) The hardness of iron is enhanced when carbon atoms are added to iron atoms in the lattice. Explain how adding carbon atoms enhance the hardness of iron in steel. …………………………………………………………………………………………..…… …………………………………………………………………………………………..…… …………………………………………………………………………………………….[1] interstitial substitution

6 [Turn Over (c) Addition of a minimum 13% chromium by mass into steel will form stainless steel which is resistant to oxidation. Suggest how adding chromium helps to prevent oxidation of the metal. …………………………………………………………………………………………..…… …………………………………………………………………………………………….[1] (d) With the aid of a labelled diagram, describe the structure and bonding in copper. …………………………………………………………………………………………..…… …………………………………………………………………………………………..…… .…………………………………………………………………………………………....[2]

7 [Turn Over (e) The diagram below is a Pourbaix diagram of iron. Any point on the Pourbaix diagram will give most stable form of the element for that electrode potential, E o and pH. The lines in the Pourbaix diagram show the equilibrium conditions where the activities are equal for the species on each side of that line. A positive value of E o denotes a strongly oxidising environment where iron is oxidised. For example, at pH 14 and Eo 0.8 V, Fe will be oxidised to FeO4 2-. Pourbaix diagrams are useful in predicting the predominant species of that element in different environments. (i) Use the Pourbaix diagram to answer the following questions: 1 Which species of iron is the strongest oxidising agent? ……………………………………………………………………………… 2 What is the range of the E o values when oxidation of Fe(OH) 2 to FexO4 take places from pH 9 to 14? ………………………………………………………………………………... Electrode potential, Eo/ V FexO4 HFeO2 -

8 [Turn Over (ii) A lake containing FeO 4 2- (aq) is very well aerated with oxygen at a pH of 5. However, due to continuous NaOH discharge from a chemical industry, reddish brown sediments of Fe 2O3 is o bserv