Mixed with water it sets back into hard gypsum. Heating gypsum above 373 K gives dead burnt plaster, which does not set.
How it is made
Heat gypsum at 373 K: CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O
Uses
Plaster casts for broken bones, statues, smooth wall finishes.
What it is made of
| Element | Atoms | % by mass |
|---|---|---|
| Ca | 1 | 27.6% |
| S | 1 | 22.1% |
| O | 4.5 | 49.6% |
| H | 1 | 0.7% |
Molar mass = 145.14 g/mol.
Common names and formulas
| Common name | Formula |
|---|---|
| Baking sodasodium hydrogen carbonate (sodium bicarbonate) | NaHCO3 |
| Washing sodasodium carbonate decahydrate | Na2CO3·10H2O |
| Soda ashanhydrous sodium carbonate | Na2CO3 |
| Bleaching powdercalcium oxychloride (calcium hypochlorite chloride) | CaOCl2 |
| Plaster of Pariscalcium sulphate hemihydrate | CaSO4·½H2O |
| Gypsumcalcium sulphate dihydrate | CaSO4·2H2O |
| Quicklimecalcium oxide | CaO |
| Slaked limecalcium hydroxide | Ca(OH)2 |
| Limestone (chalk, marble)calcium carbonate | CaCO3 |
| Common saltsodium chloride | NaCl |
| Caustic sodasodium hydroxide | NaOH |
| Caustic potashpotassium hydroxide | KOH |
| Blue vitriolcopper(II) sulphate pentahydrate | CuSO4·5H2O |
| Green vitrioliron(II) sulphate heptahydrate | FeSO4·7H2O |
| White vitriolzinc sulphate heptahydrate | ZnSO4·7H2O |
| Epsom saltmagnesium sulphate heptahydrate | MgSO4·7H2O |
| Glauber's saltsodium sulphate decahydrate | Na2SO4·10H2O |
| Potash alumpotassium aluminium sulphate dodecahydrate | K2SO4·Al2(SO4)3·24H2O |
| Boraxsodium tetraborate decahydrate | Na2B4O7·10H2O |
| Mohr's saltferrous ammonium sulphate hexahydrate | FeSO4·(NH4)2SO4·6H2O |
| Hyposodium thiosulphate pentahydrate | Na2S2O3·5H2O |
| Laughing gasnitrous oxide (dinitrogen monoxide) | N2O |
| Dry icesolid carbon dioxide | CO2 |
| Marsh gasmethane | CH4 |
| Muriatic acidhydrochloric acid | HCl |
| Oil of vitriolsulphuric acid | H2SO4 |
| Sal ammoniacammonium chloride | NH4Cl |
| Lunar causticsilver nitrate | AgNO3 |
| Chile saltpetresodium nitrate | NaNO3 |
| Saltpetre (Indian saltpetre)potassium nitrate | KNO3 |
| Calomelmercury(I) chloride | Hg2Cl2 |
| Corrosive sublimatemercury(II) chloride | HgCl2 |
| Philosopher's woolzinc oxide | ZnO |
| Red lead (sindhur)triplumbic tetroxide (lead(II,IV) oxide) | Pb3O4 |
| Liquid bleachsodium hypochlorite | NaOCl |
| Vinegarethanoic acid (acetic acid), 5–8% in water | CH3COOH |
| Table sugarsucrose | C12H22O11 |
| Spirit (grain alcohol)ethanol | C2H5OH |
| Wood spiritmethanol (methyl alcohol) | CH3OH |
| Chloroformtrichloromethane | CHCl3 |
| Carbamideurea | CO(NH2)2 |
Questions students ask
What is the chemical formula of plaster of Paris?
CaSO₄·½H₂O. Its chemical name is calcium sulphate hemihydrate.
What is the chemical name of plaster of Paris?
Calcium sulphate hemihydrate, CaSO₄·½H₂O.
What is the molar mass of plaster of Paris?
145.14 g/mol (about 145 g/mol with exam atomic masses).
How is plaster of Paris made?
Heat gypsum at 373 K: CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O.
What are the uses of plaster of Paris?
Plaster casts for broken bones, statues, smooth wall finishes.