Question

Anthraquinone contains only carbon, hydrogen, and oxygen and has an empirical formula of C7H4O. The freezing point of camphor is lowered by 22.3°C when 1.32 g anthraquinone is dissolved in 11.4 g camphor. Determine the molecular formula of anthraquinone.

Answer 1

the molecular formula is C₁₄H₈O₂

Step-by-step explanation:

Given that

The freezing point of camphor is lowered by 22.3°C

Amount of anthraquinone is 1.32g

depression constant is 40°C.kg.mol

Use the freezing-point depression equation

Molecular weight of solute, m =

`(W * 1000 * K)/(\Delta T * W)`

`= (1.32 * 1000 * 40)/(22.3 * 11.4)`

m = 208g/mol

empirical formula of Anthraquinone is C7H4O

empirical formula weight = 104 g/mol

m = Molecular formula weight / empirical formula weight

m = 208 / 104

208.2 / 104.1 = 2

molecular formula = (C₇H₄O)₂

so, the molecular formula is C₁₄H₈O₂