Question

The hydrated salt, Na
2
SO
4
. nH
2
O undergoes 55.9%loss in weight on heating and becomes anhydrous.The value of n will be

Answer 1

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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Answer 2

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