Here is a simple experiment that show the effect on an equilibrium of changing one or other of the components of that equilibrium – in this case pressure.
A small amount of soda water, coloured with methyl red indicator, is drawn up into a 50 cm3 Luer-lock syringe and capped. The plunger is then fully drawn out and secured with a nail through a hole in the plunger stem.
On shaking, CO2 comes out of solution and the resultant change in pH causes the indicator to change from red to yellow. It is possible, albeit with some effort, to apply pressure to force the CO2 back into solution and reverse the colour change.
