Visual Tips

A white background will help. For a large audience the effect is clearer if the reactions are scaled up and done in beakers.


Theory

The equilibrium is:




The shifts in equilibrium position produced both by temperature and concentration changes are in accordance with Le Chatelier's principle.

Extensions

It is possible to show that it is the ions in the hydrochloric acid that shift the equilibrium by adding a spatula of sodium chloride to the pink solution. This produces a bluer colour eventually although this takes some time to form because the salt is slow to dissolve.


Safety

Wear eye protection.