Hydrated & Anhydrous Salts (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

• When salts are being prepared, some water can be retained within the structure of the salt during the crystallisation process 
• Salts that contain water within their structure are called hydrated salts
• Anhydrous salts are those that contain no water in their structure
• A common example is copper(II) sulfate which crystallises forming the salt hydrated copper(II) sulfate, which is blue
• When it is heated, the water from its structure is removed, forming anhydrous copper(II) sulfate, which is white
• The hydrated salt has been dehydrated to form the anhydrous salt
• This reaction can be reversed by adding water to anhydrous copper(II) sulfate

hydrated copper(II) sulfate ⇌ anhydrous copper(II) sulfate + water

Hydrated copper(II) sulfate and anhydrous copper(II) sulfate

Diagram showing the dehydration of hydrated copper(II) sulfate