What are hydrous substances? Explain with examples.

Substances which contain water molecules along with salts like Sodium carbonate decahydrate [Washing soda crystals — Na₂CO₃.10H₂O] and Copper (II) sulphate pentahydrate [Blue vitriol — CuSO₄.5H₂O] are hydrated substances. This water gives the crystals their shape. In some cases it also gives them their colour (copper sulphate crystals are blue in colour).