Redox, group 2, group 7 exam qs
AS LEVEL CHEMISTRY
REDOX GROUP 2 GROUP 7
Answer all questions
Max 39 marks
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Mark ……../39 ……....% Grade ……… Redox, group 2, group 7 exam qs
1. The Group 2 element radium, Ra, is used in medicine for the treatment of cancer. Radium was discovered in 1898 by Pierre and Marie Curie by extracting radium chloride from its main ore pitchblende.
(a) Predict the formula of radium chloride.
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(b) Pierre and Marie Curie extracted radium from radium chloride by reduction. Explain what is meant by reduction, using this reaction as an example.
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2. The Group 2 metal strontium, Sr, is very reactive.
Strontium metal is stored under oil and, when exposed to air, the shiny surface of the strontium becomes dull.
Predict, with an equation, what reaction takes place when strontium is exposed to air.
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3. The reaction of strontium with water is a redox reaction.
Sr(s) 2H2O(l) Sr(OH)2(aq) H2(g)
Use oxidation numbers to show that strontium has been oxidised in this reaction.
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...... [Total 2 marks] Redox, group 2, group 7 exam qs 4. When barium metal is added to water, the reaction taking place is much more vigorous than with calcium.
Explain why barium is more reactive than calcium.
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5. A student prepared an aqueous solution of calcium chloride by reacting calcium with hydrochloric acid.
Ca(s) + 2HCl(aq) → CaCl2(aq) + H2(g)
(i) Using oxidation numbers, show that this is a redox reaction.
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(ii) The student had added the exact amount of calcium required to react with the hydrochloric acid used. After carrying out the experiment, the student accidentally added some more calcium. The student was surprised that the extra calcium still reacted.
Explain this observation. Include an equation in your answer.
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...... [2] [Total 4 marks] Redox, group 2, group 7 exam qs 6. Carbon dioxide can be prepared easily in the laboratory by the action of heat on most carbonates. Construct an equation to illustrate this reaction.
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7. At room temperature and pressure, r.t.p., chlorine is a gas, bromine is a liquid and iodine is a solid.
Explain why these halogens have different physical states at r.t.p.
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Redox, group 2, group 7 exam qs
8. In this question one mark is available for the quality of spelling, punctuation and grammar.
Chlorine gas was bubbled through an aqueous solution of bromide ions and also through an aqueous solution of iodide ions. An organic solvent was then added and each mixture was shaken.
• State what you would see in each case.
• Write equations for any chemical reactions that take place.
• State and explain the trend in reactivity shown by these observations.
(Allow one lined page).
[6] Quality of Written Communication [1] [Total 7 marks] Redox, group 2, group 7 exam qs 9. Aqueous silver nitrate can be used as a test for halide ions. A student decided to carry out this test on a solution of magnesium chloride. The bottle of magnesium chloride that the student used showed the formula MgCl2.6H2O.
The student dissolved a small amount of MgCl2.6H2O in water and added aqueous silver nitrate to the aqueous solution.
(i) What would the student see after adding the aqueous silver nitrate, AgNO3(aq)?
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(ii) Write an ionic equation for this reaction. Include state symbols.
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(iii) Using aqueous silver nitrate, it is sometimes difficult to distinguish between chloride, bromide and iodide ions.
How can aqueous ammonia be used to distinguish between these three ions?
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10. Domestic tap water has been chlorinated.
Chlorine reacts with water as shown below.
Cl2(g) H2O(l) HOCl (aq) HCl (aq)
(i) State the oxidation number of chlorine in
Cl2 ......
HOCl ......
HCl ...... [3]
(ii) When carrying out halide tests with aqueous silver nitrate, it is important that distilled or deionised water is used for all solutions, rather than tap water.
Suggest why.
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11. Chlorine is used in the preparation of many commercially important materials such as bleach and iodine.
Bleach is a solution of sodium chlorate(l), NaOCl, made by dissolving chlorine in aqueous sodium hydroxide.
Cl2(g) 2NaOH(aq) NaOCl(aq) NaCl(aq) H2O(l)
Determine the changes in oxidation number of chlorine during the preparation of bleach and comment on your results.
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