Water of Crystallisation  Explain the terms: anhydrous, hydrated; and water of crystallisation.  Calculate the formula of a hydrated salt using percentage composition, mass composition or experimental data.

When crystals of certain salts are formed, they do so with a definite number of molecules of water - this is chemically combined in a definite proportion. The Water of crystallization is the number of water molecules chemically combined with the salt in its crystalline state. This water is responsible for the geometric shape and colour of the crystals. Water of crystallization

On heating, hydrous crystals lose their water of crystallization and turn into a powder. They are then said to be anhydrous. Sometimes they may also lose their colour.

Name Chemical Formula Common Name Barium chloride BaCl 2.2H 2 O Calcium chloride CaCl 2.6H 2 O Dow flake Calcium nitrate Ca(NO 3 ) 2.4H 2 O Lime salt petre or Norwegian salt petre Calcium sulphate CaSO 4.2H 2 O Gypsum Calcium sulphate semi hydrate (CaSO 4 ).½. H 2 O Plaster of Paris Copper (II) chloride CuCl 2.2H 2 O Copper (II) sulphate CuSO 4.5H 2 O Blue vitriol Ferrous sulphate FeSO 4.7H 2 O Green vitriol Zinc sulphate ZnSO 4.7H 2 O White vitriol Magnesium sulphate MgSO 4.7H 2 O Epsom salt Potassium aluminium sulphate K 2 SO 4.Al 2 (SO 4 ) 3.24H 2 O Potash alum Sodium carbonate deca hydrate Na 2 CO 3,10H 2 O Washing soda (crystal) Sodium sulphate Na 2 SO 4.10H 2 O Glauber’s salt

Hydroscopic salts have the ability of a substance to attract water molecules from the surrounding environment Deliquescence Deliquescent materials are substances have a strong affinity for moisture and will absorb relatively large amounts of water from the atmosphere if exposed to it, forming a liquid solution. examples are : instant coffee potassium hydroxide and sodium hydroxide. and the opposite is... Efflorescence (which means "to flower out" in french) is the loss of water (or a solvent) of crystallization from a hydrated or solvated salt to the atmosphere on exposure to air.

Effervescence Effervescence is the escape of gas from an aqueous solution and the foaming or fizzing that results from a release of the gas.gasaqueous solution The word effervescence is derived from the Latin verb fervere preceded by the adverb ex, which means to boil.Latin It has the same linguistic root as the word fermentation.fermentation So its not bubbles or bubbling !!

Tasks Key definitions Hydrated.. Anhydrous.. Water of crystallisation... Examiners tip is.. Worksheet Questions : 1, 2, 3