Displacement Reactions
Displacement Reactions
Practical Skills Development
- Safe use and careful handling of gases, liquids and solids, including:
- Careful mixing of reagents under controlled conditions,
- Using appropriate apparatus to explore chemical changes and/or products
- Presenting observations and other data using appropriate formats
Aim
- To use displacement reactions to identify the reactivity trend of Group 7 elements
Health & Safety Aspects
- Cyclohexane is also highly flammable so should not be near open flames
- Chlorine and bromine water are harmful so should be handled carefully and safety goggles worn
- The fumes from chlorine and bromine are unpleasant so the reactions should be carried out in a well ventilated area or fume cupboard
- Small volumes should be used to minimise the risk of these hazardous substances
- Due to the hazards present this experiment is best carried out as a teacher demonstration
Materials
- spotting or dimple tile
- 0.1% solutions of Cl2, Br2 and I2
- 0.1 mol / dm3 solutions of KCl, KBr and KI
- cyclohexane, C6H12
- Universal indicator paper
Method
- Three drops of the halogens are added to separate wells in the dimple tile and the colours recorded
- In a second set of wells, the same three halogen solutions are added separately, followed by three drops of potassium chloride
- The procedure is repeated in a third and fourth set of wells using potassium bromide and potassium iodide , respectively
- The colours of the resulting solutions are noted
- The halogen colours are more easily seen if they are withdrawn in a pipette and added to a test tube containing 1-2 cm depth of cyclohexane and shaken
- Finally, a piece of universal indicator is added, in turn, to each of the halogen solutions and the colour recorded
- Record all observations in suitable tables
Results
The Colour of the Halogen Solutions
The Reactions of Halogens with Halide Ions
The Effect of Halogen Solutions on Indicator Paper
Conclusions
- Chlorine appears to displace bromine and iodine from solutions of their compounds
- Bromine displaces iodine from solutions of its compounds
- A more reactive halogen displaces a less reactive one
- The order of reactivity from this experiment is chlorine > bromine > iodine
- Chlorine is a strong bleaching agent, bromine less so and iodine not at all