Q.
The cryoscopic constant for acetic acid is 3.6Kkg/mol. A solution of 1g of a hydrocarbon in 100g of acetic acid freezes at 16.14∘C instead of the usual 16.60∘C. The hydrocarbon contains 92.3% carbon. What is the molecular formula?
Kb=3.6Kkg/mol ΔTf=16.6−16.14=0.46∘C ΔTf=m1w21000kfw1 0.46=m1×1001000×3.6×1 m1=0.4636=78.26g C=10092.3×78.26=72.23g H=1007.7×78.26=6.026g
Whole ratio C=1272.23=6.02 H=16.026=6.02
Therefore, the molecular formula is C6H6