Calcium Carbonate ( CaCO3) is almost everywhere: from egg shells, pearl, rocks to chalks we use on blackboard,etc. It is such an important material that we need to know about its properties and applications. OK, most of the time the calcium carbonate we find in mines are not 100% pure. In order to purify that to meet industrial standards, we ususally convert it to calcium oxide and carbon dioxide by calcining it. Then we add water to the calcium oxide produced and that produces calcium hydroxide solution. Finally when carbon dioxide gas passes through the solution, it will form calcium carbonate again, but at a higher purity.       Calcium Carbonate is a weak basic salt. It will react with acid to produce carbon dioxide. This is one way to identify calcium carbonate.  Since calcium carbonate is white, it is often used in white paint. Also, for the ultra white paper we use in office, there is calcium carbonate mixed in it and that is why it looks so white. For buildings that are made with calcium carbonate (cement is made from calcium carbonate, there is one disadvantage -- when acid rain comes, these buildings are more likely to get corroded. So maintaince of these kinds of buidings have become a headache to construction developers. That is why we do so many things to avoid acid rain.