A crystalline salt on being rendered anhydrous loses 45.6% of its weig

A crystalline salt on being rendered anhydrous loses 45.6% of its weight. The composition of anhydrous salt is: Al= 10.5%, K= 15.1 % , S=24.8 % and 0=49.6% Calculate the formula of anhydrous salt and crystalline salt.

Answer»

Therefore, The simples formula of anhydrous = KAlS₂O₈

molecular weight for anhydrous = 258 g/mole.

Let say molecular weight of crystalline = x g/mol.

∴ \(\frac{(x-258)}x\times100=45.6\)

⇒ (x - 258) = 0.456 x

⇒ 0.544 x = 258

x = 474.26 f/mol

∴ Number of water molecular in crystalline = \(\frac{474.26-258}{12}=12\)

Thus, crystalline contains 12 molecule of water.

Therefore, The formula of crystalline will be

KAlS₂O₈.12H₂O

Or KAlH₂₄S₂O₂₀

Hence, The formula of crystalline and anhydrous will be KAlS₂O₈.12H₂O and KAlS₂O₈ respectively.