1.615 g of an anhydrous salt was placed in moist air . After a few days it was found to be 2.875 g . Assuming that complete hydration has taken place , calculate the simplest formula of hydrated salt . The composition of anhydrous salt is Zn=40.6%;S=19.8%;O=39.6%.

symbol	weight	Molecular weight	moles	Ratios of moles	Simplest whole no. ratio
Zn	40.6 g	65.3	40.6/65.3=.621	.62/.61	1
S	19.8 g	32	19.8/32=.618	.61/.61	1
O	39.6	16	39.6/16=2.475	2.475/.61	4

 Hence, empirical formula is ZnSO₄

Weight of ZnSO₄ .XH₂O(Hydrated salt)/weight of ZnSO₄(Anhydrous salt)=Molecular weight of ZnSO₄.XH₂O/Molecular weight of ZnSO₄

(2.875)/1.615=(161.3+18x)/161.3

x=6.99=7.00

hence, x=7

so we can write it as ZNSO_4.7H₂O