1.

An organic compound (A) contains C and H only (C=90%). (A) produces another compound (B) on treatment with HBr. (B) contains 79.2% of Br. If the molecular weight of (A) is 40, find the formulae of (A) and (B). (Br= 80)

Answer»

Solution :MOLES of `C= (90)/(12)= 7.5`
Moles of `H= (10)/(1)=10`
`therefore` moles of `C:H= 7.5: 10`
=`3:4`
`therefore` empirical formula is `C_(3)H_(4)`
As molecular weight is 40, the molecular formula, will be the same as the empirical formula i.e., (A) is
`CH_(3)- C -= CH or, CH_(2)=C= CH_(2)`
SINCE with HBr, (A) will produce `CH_(3)-C(Br_(2))- CH_(3)` in which Br % `=(160)/(202)XX 100=79.2%`
Which is the same as the GIVEN value, (B) will be `CH_(3)-C(Br_(2))-CH_(3)`


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