Videos
How To Demonstrate Le Châtelier’s Principle
In this short video, Paul Cook will show you Le Châtelier’s Principle by demonstrating the reversible equilibrium reaction by change of temperature using cobalt ions. Make sure to watch until the end for extra tips!
Le Chatelier’s principle describes how, when a dynamic equilibrium is disrupted by a change of pressure, temperature, volume or concentration, the position of equilibrium will shift to counteract any change and restore an equilibrium state.
The equilibrium reversible reaction of two-coloured cobalt species due to a change of temperature.
Le Chatelier’s principle, when the temperature has raised the equilibrium of the chloride ions in the solution will change and a blue complex of ions is formed in expense of the pink species.
Cooling the solution will reverse this reaction and the equilibrium moves to a pink complex of ions.
Equipment List
- Cobalt (II) chloride -6-water 0.5g (Toxic, Dangerous for the Environment)
- Concentrated HCl (Corrosive) 50ml dropper
- 2 x boiling tubes with fitting bungs
- 2 x tall form 250ml beakers
- 250ml beaker
- 400ml beaker or Test tube rack
- Stirrer/glass rod
- 50ml measuring cylinder
- Pipette
- Balance
- Weighing boat
- Gratnells tray / laminated A4 white sheet
- Ice
- Kettle
- Access to water.
- Lab coat
- Safety glasses
- Disposable gloves
Method
- Wearing safety glasses and gloves weigh out the Colbalt (II) Chloride solid.
- In a fume cupboard using a 250ml beaker make a 50ml Colbalt Chloride solution by dissolving the Colbalt Chloride solid in distilled water and adding drops of the concentrated Hydrochloric acid until the desired pink colour is obtained.
- Using the measuring cylinder add 25ml of the solution to each of the boiling tubes and fit the bungs
Demonstration Time
- Wearing safety glasses, lab coat and gloves
- Hold the two bunged boiling tubes in a 400ml beaker or Test tube rack.
- Boil a kettle
- Prepare ice cubes
- Place the two 250ml tall form beakers into the tray on the laminated white sheet.
- Create two water baths;
- Add ice cubes and water to one of the tall form beakers. Place one of bunged boiling tubes in and check the iced water level is equal or above the level in the boiling tube.
- Using hot kettle water (not boiling) do the same for the second tall form beaker. Careful adding second boiling tube!! Keep pressure on the bung (otherwise the hot water will cause it the bung to pop off)
- Watch the colour change
- Then swap the tubes over, taking care to hold down the bung of the tube now going into the hot water.
- Now watch the colours reverse in the different temperature water baths.
- This can be repeated as many times as the water baths remain hot & cold.
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