Question

Why is calcium sulphate hemihydrate called Plaster of Parus

Answer 1

Hi,

The name plaster of Paris comes from the fact that it was first made by heating gypsum which was mainly found in Paris.It is called hemihydrates due to the fact that two molecules of calcium sulphate share a single water molecule. Thus each calcium sulphate molecule get only half the share of water molecule and hence hemihydrates.