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

Hydrated & anhydrous salts

• 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