Doc Brown's Chemistry
A Periodic Table task sheet on the Group 7 The Halogens
Worksheet questions on the properties of elements and compounds and their uses
Revision KS4 Science IGCSE/O level/GCSE Chemistry Information Study Notes for revising for AQA GCSE Science, Edexcel GCSE Science/IGCSE Chemistry & OCR 21stC Science, OCR Gateway Science (revise courses equal to US grades 9-10)
Task 1: The properties of the Group 7 Halogen elements
1. (a) Complete the table above.
2. (a) What properties in the table are typical of non-metals?
3. (a) What is the group trend in melting and boiling point down the group with increase in atomic number?
4. The molecules consist of diatomic molecules. What does this mean?
5. (a) What sort of compounds do they form when combined with metals?
6. What sort of compounds do they form when combined with non-metals? eg hydrogen chloride HCl
7. Describe simple chemical tests for (a) chlorine, (b) iodine [clue - biological connection]
Task 2: The Reactivity Trend of the Halogens
This may be done by you or demonstrated by the teacher
What you do is add a solution of the halogen in water to the potassium salts of the other halogens, also dissolved in water. If a displacement reaction occurs the solution gets darker (eg more yellow, orange or brown). It also shows whether one halogen is more reactive than another. Note your observations in the table below.
1. (a) complete the table of results above, either from doing the experiment or working it out from your knowledge of halogen chemistry.
2. (a) Which halogens does chlorine displace?
3. (a) What is the reactivity rule for displacement reactions?
4. From your observations in 2. write word and symbol equations for the other displacement reactions that happened.
5. is higher GCSE students really and involves using redox and electronic theory
5. Write word and ionic equations for the reactions and explain them in terms of oxidation and reduction (electron loss or gain). The equations only involve the halogen molecules and halide ions. Note the potassium ion K+, does not take part in the reaction and is called a 'spectator ion'. The first equation is given BUT not fully balanced ... and then write out the others where a reaction took place
6. Why do elements in the same group have similar chemical properties?
7. How, in electronic terms, do you explain the reactivity trend?
Task 3: The Electrolysis of Sodium chloride Solution (Brine)
Sodium chloride (NaCl, common salt) is a compound of an alkali metal and a halogen. It is found in large quantities in the sea and in underground deposits. It is a most important raw material for the chemical industry. The cheapest sources are (i) evaporation of seawater and (ii) pumping water down into salt deposits to dissolve it, and then evaporating the pumped out solution (called brine). It is far to costly to make the salt by neutralisation.
From salt lots of products can be made.
The electrolysis of sodium chloride solution (brine) is an important industrial process.
In can be demonstrated in the laboratory using a simple electrolysis cell (shown in the diagram).
1. (a) Would the water be a good conductor without the salt in it?
2. What do you see when the current is witched (i) ON and (ii) OFF?
3. The gases and solutions can be tested in various ways ...
higher GCSE students need to do the electrode equations - balancing and redox theory
The ions present in the solution are Na+ and Cl- from the salt and traces of H+ and OH- from water.
From your electrolysis experiment observations and using redox theory ....
4. (a) which ions will move towards the negative electrode? which one must have changed to form the gas?
Task 4: The Uses of the Halogens and their compounds
1. Which halogen is used for treating domestic water supplies and swimming pool water? What does it do?
2. Find out four cases where chlorine is changed to another useful compound or material, and briefly describe the uses of them.
3. Find out two uses of hydrogen gas in the manufacture of other products.
4. Find out three products that use sodium hydroxide in their manufacture
5. (a) Which compounds of the halogens are used for photographic film?
6. (a) What is formed on combining chlorine and hydrogen? and describe the product.
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