Question

MOLE CONCEPT problems on empirical & molecular formula 

Two organic compounds 'X' and 'Y' containing carbon and hydrogen only, have vapour densities 13 and 39 respectively. State the molecular formula of 'X' and 'Y' [C=12 , H=1] 

PLEASE SHOW THE WORKING!!

Answer 1

for the compound X : given VD=13.
                                  we know that molecular wt=2 * VD
                                 therefore.mol.wt of X=2*13        
                                                              =26
              emp formula wt=12+1=13
 ⇒         n=mol.mass/emp formul mass=26/13=2
             formula of compound =C₂H₂     
similarly for the compound Y: mol. wt=2*vd
                                           mol wt=2*39=78
                                          emp formula wt=12+1=13
                                        n=78/13=6
                                       formula of the compund is C₆H₆

Answer 2

Molecular Formula

X = C2H2

Y=C6H6