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ICSE Class 10 Chemistry 2015 Paper

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Question : 13 of 85
Marks: +1, -0
If the empirical formula of a compound is CH\mathrm{CH} and it has a vapour density of 13, find the molecular formula of the compound.
Solution:  
  Molecular formula   =CH\,\text{ Molecular formula }\,\,= \mathrm{CH}
  V.D.   =13\,\text{ V.D. }\,\,=13
  Mol. Mass   =2×  V.D.  \,\text{ Mol. Mass }\,\,=2 \times \,\text{ V.D. }\,
 =2×13=26\,=2 \times 13=26
Empirical formula weight of CH\mathrm{CH}
 =12+1=13\,=12+1=13
n =   Mol. Mass    Emp. formula Mass  n\,=\,\frac{\,\text{ Mol. Mass }\,}{\,\text{ Emp. formula Mass }\,}
 = 2613=2\,=\,\frac{26}{13}=2
Molecular formula =(Emp.  formula  )n=(\mathrm{Emp}.\,\text{ formula }\,)_n
=(CH)2=C2H2=(\mathrm{CH})_2= \mathrm{C}_2 \mathrm{H}_2
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