The majority of plants grow best at pH 7. If the soil is acidic or alkaline the plant may grow badly. Therefore, chemicals can be added to the soil to change its pH.
If the soil is too acidic - the most common complaint - it is treated with a base (chemicals opposite to an acid) in order to neutralise it. Common treatments use quicklime (calcium oxide) or chalk (calcium carbonate).
We all have hydrochloric acid in our stomach - it helps breakdown food! However, too much acid leads to indigestion. Therefore, to cure this ailment we need to neutralise the acid with a base such as, sodium hydrogen carbonate (baking soda), or an indigestion tablet.
A bee sting contains acid. In order to relieve the painful symptoms of the sting we need to neutralise the acid. By rubbing on calamine lotion (zinc carbonate) or baking soda the acid can be neutralised.
Wasp stings are alkaline, hence acid is needed to neutralise and remove the painful sting. Vinegar (ethanoic acid) is used.
Waste from Factories
Waste from many factories are often acidic. If this acidic solution is not treated and enters rivers it can kill fish. Slaked lime (calcium hydroxide) is often used to neutralise the acid.