Theory

The relevant neutralisation equations are:


with ammonia

(l) + (aq) + (g) NH(aq) + HCO(aq)


with sodium hydroxide

OH(aq) + (g) HCO (aq)

Extensions

Other indicators can be used such as phenolphthalein (pink to colourless), thymolphthalein (blue to colourless), thymol blue (blue to yellow), phenol red (red to yellow) and bromothymol blue (blue to yellow).


Safety

Wear eye protection and use gloves to handle the dry ice as it can cause frostbite burns.