“Lime” comes in 3 different forms:
1. Calcium carbonate, CaCO3
Also called garden lime, agricultural lime
, (and if it contains also some Magnesium: Dolomite
). It occurs naturally in limestone deposits, like around Buchan in Gippsland, in the Burgundy, France, and where I come from near Basle in Switzerland. It doesn’t harm plants or animals
but can be used to counteract soil acidity.
2. Calcium oxide, CaO.
-> CaO + CO2
Lime used to be ‘burnt’, in lime kilns, which are still around in limestone areas, and ‘burning’, which is simply dry heating, then produces Calcium Oxide, also called burnt lime, quick lime and unslaked lime
. Calcium oxide is highly reactive, as it takes up moisture from the air (or from living tissue) very quickly, forming a caustic
product, Calcium hydroxide. Therefore it destroys living tissue
. It burns plants, animals and skin etc. Breathing it in is not recommended, or getting it on skin.
3. Calcium hydroxide, Ca(OH)2
CaO + H2
O -> Ca(OH)2
When above burnt lime is mixed with water a very violent reaction called ‘slaking’ takes place, and the product is ‘slaked lime’, also called calcium hydrate, hydrated lime, lime hydrate, builders lime
. Builders lime is caustic
and again burns skin. It is the lime used for white washing buildings, however a pH of 10-12 will burn skin easily.
Calcium hydroxide, as a caustic, will react with any acid, like Carbonic acid to give ‘garden lime’ again, so if exposed to air will become harmless once more.
Yes, I'm a chemist, so what?