Question

A 7.85g sample of a cpd with the empirical formula C5H4 is dissolved in 301g of benzene.. The freezing point of the solution is 1.05'C below that of pure benzene. What are the molar mass n molecular formula of this cpd??

Answer 1

According to Raul’s law for solutions of non-electrolytes:

$$\Delta T_{fr} = iKm$$ $$i = 1$$ $$K_{benzen} = 5.12$$

$$m = {\Delta T_{fr} \over K} = {1.05 \over 5.12} = 0.205mol/kg$$

$$n_{sample} = m*m_{benzene} = 0.205mol/kg*0.301kg = 0.062mol$$

$$M_{sample} = m_{sample}/n_{sample} = 7.85g/0.062mol = 126.6g/mol$$

Molecular formula C₁₀H₈ (probably it's naphthalene)