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%.

Asked by Ujjwal Kumar | 6th Oct, 2010, 10:04: AM

Expert Answer:

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 ZNSO4.7H2O

Answered by  | 6th Oct, 2010, 11:12: PM

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