1.

In a compound, C, H and N are present in the ratio `9 : 1: 3.5` by weight. If the molecular weight. If the molecular weight of the compound is 108, what is the number of hydrogen atoms present in the molecular formula of the compound ?

Answer» Correct Answer - `=8`
Step I. Empirical formula of the compound
`{:("Element","Percentage/weight (ratio)","Gram atoms (Moles)","Atomic ratio (Molar ratio)","Simplest whole no. ratio"),("C",9,(9)/(12)=0.75,(0.75)/(0.25)=3,3),("H",1,(1)/(1)=1.0,(1.00)/(0.25)=4,4),("N",3.5,(3.5)/(14)=0.25,(0.25)/(0.25)=1,1):}`
Empirical formula of the compound `= C_(3)H_(4)N`
Step II. Molecular formula of the compound
Empirical formula mass `= 3 xx 12 + 4 xx 1 +14 = 54 u`
Molecular mass = 108 u (given)
`n=("Molecular mass")/("Empirical formula mass")=((108u))/((54u))=2`
Molecular formula of the compound `= n xx` Empirical formula
`:.` Number of hydrogen atoms present = 8.


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