Quick answer: Group 1 metals have one outer electron and become more reactive down the group, reacting with water to make hydrogen and an alkaline hydroxide. This Chemistry 9-10 lab on periodic table groups gives the aim, the equipment, the safety points, a step-by-step method, sample results and 7 analysis questions; the answers are on a separate page and the lab sheet is a free printable PDF.
Which halogen is the most reactive? You will mix three halogen solutions with three potassium halide solutions, record the colour changes, and use the pattern of displacement to place the halogens in order of reactivity.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: GCSE C1, IGCSE 9
Aim
To find the order of reactivity of chlorine, bromine and iodine by displacement reactions in solution.
Equipment
- Chlorine water, bromine water and iodine solution (dilute, prepared by the teacher)
- 0.1 mol/dm³ potassium chloride, potassium bromide and potassium iodide solutions
- Nine small test tubes and a rack, white tile
- Dropping pipettes and a marker
Safety
Wear goggles and gloves. Halogen solutions are toxic and irritate the skin and eyes, even when dilute. Work in a ventilated room, keep the tubes away from your face, and wash spills with plenty of water. Dispose of the waste as your teacher instructs.
Method
- Label three tubes for each halogen.
- Add 1 cm³ of potassium chloride, bromide and iodide solutions to the three tubes of each halogen.
- Add 1 cm³ of one halogen solution to each of its three tubes. Shake gently.
- Stand the tubes against the white tile and record any colour change.
- Compare each tube with a control containing only the halogen solution and water.
Results
| Halogen added | Potassium chloride | Potassium bromide | Potassium iodide |
|---|---|---|---|
| Chlorine water (pale green) | No change | Orange solution | Brown solution |
| Bromine water (orange-yellow) | No change | No change | Brown solution |
| Iodine solution (brown) | No change | No change | No change |
Analysis questions
Question 1 Which reactions occurred
State which mixtures showed a reaction and which did not.Question 2 Write the equations
Write balanced equations for the three reactions that occurred.Question 3 Order of reactivity
Use the results to place the three halogens in order of reactivity, with the most reactive first.Question 4 Explain with electrons
Use the number of shells to explain why chlorine is more reactive than iodine.Question 5 Why use a control
Explain why a control tube with the halogen and water only is needed to judge a result such as iodine with potassium iodide.Question 6 Make the tests fairer
Suggest two changes that would make the colour judgements more reliable.Question 7 Predict for astatine
Predict whether iodine would displace astatine from sodium astatide, and explain your reasoning.
