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CBSE Class 11-science Answered

What is the simplest formula of the compound which has the following percentage composition? Carbon 80% and Hydrogen 20%. If the molecular mass is 30, calculate its molecular formula.
Asked by Topperlearning User | 15 Jun, 2016, 01:27: PM
answered-by-expert Expert Answer

Calculation of empirical formula:

Element
Percentage
Atomic mass
Relative number of moles
Simple ratio
Simplest whole number ratio
C
 
 
H
80
 
 
20
12
 
 
1
begin mathsize 11px style 18 over 12 space equals space 6.66 20 over 1 space equals space 20 end style
begin mathsize 11px style fraction numerator 6.66 over denominator 6.66 end fraction space equals space 1 fraction numerator 20 over denominator 6.66 end fraction space equals space 3 end style
 
1
 
 
3
 
Therefore Empirical formula is CH3
 
Calculation of molecular formula:
 
Empirical formula mass = 12 × 1 + 1 × 3 = 15

begin mathsize 11px style straight n space equals space fraction numerator Molecular space mass over denominator Empirical space formula space mass end fraction space equals space 30 over 15 space equals space 2 end style

Molecular formula = Empirical formula × 2
 
                          = CH3 × 2 = C2H6
Answered by | 15 Jun, 2016, 03:27: PM

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