The hydrated salt, Na₂SO₄.nH₂O undergoes 55.9% loss in weight on heating and becomes anhydrous. The value of n will be :

Molecular Mass of Na₂SO₄ is =2X23 + 32 + 4X16 = 142 gm.

To know the mass of Na₂SO₄ containing 55.9% H₂O , we subtract 55.9 from 100 .

100-55.9= 44.1

Therefore 44.1 g Na₂SO₄ contains --- 55.9 gm H₂O

So, 1gm Na₂SO₄ contains ---- 55.9 / 44.1 gm H₂O

142 gm Na2SO4 contains ----- 55.9 /44.1 X 142 = 180 gm H₂O .

Now we have to find the number of water molecules . This will be the value of n as is asked in the question .

Number of water molecules = 180 / 18 (Since Molecular mass of H₂O is 18).

= 10 water molecules .

Hence the value of n is 10 and the formula is Na₂SO₄.10H₂O.

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