Water of Crystallization

 Hello fam! Today we would be looking at the water of crystallization of a salt. It is common to refer to some salts as hydrates. A hydrate is a salt that has its water of crystallization attached to its structure.


The term water of crystallization refers to the number of water molecules that combine chemically, in definite molecular proportion with a salt to form a crystalline structure. The number of water molecules attached to the crystal lattice of the salt is usually written alongside the chemical formula of the salt by placing a dot in between the usual formula of the salt and the number of molecules of water attached to the salt lattice.


Examples of salts having water of crystallization are;

• Na2CO3.10H2O – Sodium carbonate decahydrate

• CuSO4.5H2O  - Copper sulfate pentahydrate

• CaSO4.2H2O – Calcium sulfate dihydrate 


It is important to note that the presence or absence of the water of crystallization affects the properties of the salt. For instance, CuSO4.5H2O is blue in color. When we heat this hydrated salt so that the five molecules of water of crystallization are driven off, the anhydrous salt is formed (CuSO4) without the five molecules of water of crystallization. This anhydrous salt is white in color.


Though a sample of CuSO4.5H2O (blue color) appears completely dry, when heated strongly in a dry test tube, water droplets will appear on the walls of the test tube as the substance changes from blue to white color.


Hydrates can be obtained when a saturated solution of the concerned salt is cooled. It should be noted that not all existing salts contain water of crystallization. However, hydrated salts retain a definite crystal structure with the water molecules neatly tucked into the crystal lattice of the salt.


Tomorrow, we shall look at how to calculate the number of moles of water of crystallization in the chemical formula of a hydrated salt. Join us then!

Hello fam! Today we would be looking at the water of crystallization of a salt. It is common to refer to some salts as hydrates. A hydrate is a salt that has its water of crystallization attached to its structure.


The term water of crystallization refers to the number of water molecules that combine chemically, in definite molecular proportion with a salt to form a crystalline structure. The number of water molecules attached to the crystal lattice of the salt is usually written alongside the chemical formula of the salt by placing a dot in between the usual formula of the salt and the number of molecules of water attached to the salt lattice.


Examples of salts having water of crystallization are;

• Na2CO3.10H2O – Sodium carbonate decahydrate

• CuSO4.5H2O  - Copper sulfate pentahydrate

• CaSO4.2H2O – Calcium sulfate dihydrate 


It is important to note that the presence or absence of the water of crystallization affects the properties of the salt. For instance, CuSO4.5H2O is blue in color. When we heat this hydrated salt so that the five molecules of water of crystallization are driven off, the anhydrous salt is formed (CuSO4) without the five molecules of water of crystallization. This anhydrous salt is white in color.


Though a sample of CuSO4.5H2O (blue color) appears completely dry, when heated strongly in a dry test tube, water droplets will appear on the walls of the test tube as the substance changes from blue to white color.


Hydrates can be obtained when a saturated solution of the concerned salt is cooled. It should be noted that not all existing salts contain water of crystallization. However, hydrated salts retain a definite crystal structure with the water molecules neatly tucked into the crystal lattice of the salt.


Tomorrow, we shall look at how to calculate the number of moles of water of crystallization in the chemical formula of a hydrated salt. Join us then!


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