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C.U.P. CHEMISTRY TEST 2 2011 (2)
Wednesday 24 August 2.10 – 3.00 p.m.
Time allowed: 50 minutes. This test contains 4 pages. total 44 marks
Answer on these pages. A periodic table is attached to this test.
Show your working in all calculations and give units where appropriate.
UC Student Number_______________
State whether each of the following compounds will be ionic or covalent 
1. MnO2 2. ZnCl2
3. SiF4 4. BaS
Write down the oxidation number of chlorine in each of these compounds or ions: 
5. ClO3– 6. Ca(OCl)2 7. Cl2O
8. The bonds in a molecule of water are described as polar.
Explain (a) what polar means, and (b) why these particular bonds are polar.
9. One type of lithium battery used the following redox reaction to generate electrical energy:
2Li + 2MnO2 + H2O → 2Li+ + Mn2O3 + 2OH–
[molar masses in g mol–1: Mn = 54.9, O = 16.0, Li= 6.9]
a. What is the molar mass of MnO2? 
b. What mass of MnO2 would be needed to react with 1.0 g of lithium? 
For each of the following molecules, (a) draw the Lewis diagram and (b) predict the expected molecular shape. 
12. A dilute solution of iodine can be used to kill harmful microorganisms in drinking water. To find the concentration of iodine in such a solution, a student titrated 20.0 mL samples of it against standard 0.05240 mol L–1 thiosulfate solution:
I2 + 2S2O32( ( 2I( + S4O62–
The average titre was 17.55 mL of S2O32(.
a. Name an indicator that could be used to make the end-point more distinct. 
b. If this indicator is used, describe the colour change at the end-point. 
c. Calculate the amount of standard solution used up in the reaction. Show all working. 
d. Calculate the concentration of the iodine solution. Show all working. 
13. When using a burette in a titration, a number of precautions must be observed to ensure accuracy. Describe two of these precautions and the reasons behind them. 
The following reactions (questions 14-15) take place under acidic conditions. Complete and balance the redox equations using the ion-electron method. Show working clearly.
14. Cr2O72–(aq) + Fe2+(aq) ( Cr3+(aq) + Fe3+(aq) 
15. MnO2(s) + NO2–(aq) → Mn2+(aq) + NO3–(aq) 
16. Describe the observations that would be made when reaction 14 is carried out. 
17. In question 15 above, which element has been oxidised? 
18. Complete the table below by describing the type of attractive force between particles that breaks when each substance melts. 
Choose your answers from the list below. You may use answers more than once, or not at all.
attraction of atoms for shared electrons
attraction between + and – ions
attraction between cations and mobile electrons
attraction between permanent dipoles
attraction involving temporary dipoles
substance melting temperature/oC attractive force that must be broken iron +1535 silicon dioxide (quartz, SixO2x) +1713 hydrogen bromide –87
19. Explain why liquid (melted) sodium chloride conducts electricity, but solid sodium chloride does not. 
END OF TEST