Question

When 0.49 g of a molecular compound was dissolved in 20.00 g of cyclohexane, the freezing point of the solution was lowered by 3.9 0C. Determine the molecular mass of this compound.

Answer 1

Answer: The molecular mass of this compound is 131 g/mol

Step-by-step explanation:

Depression in freezing point:

`\Delta T_f=i* k_f* (w_2* 1000)/(M_2* w_1)`

where,

`\Delta T_f` = depression in freezing point =
`3.9^oC`

`k_f` = freezing point constant =
`20.8^0C/m`

m = molality

i = Van't Hoff factor = 1 (for non-electrolyte)

`w_2` = mass of solute = 0.49 g

`w_1` = mass of solvent (cyclohexane) = 20.00 g

`M_2` = molar mass of solute = ?

Now put all the given values in the above formula, we get:

`(3.9)^oC=1* (20.8^oC/m)* ((0.49g)* 1000)/(M_2* (20.00g))`

`M_2=131g/mol`

Therefore, the molar mass of solute is 131 g/mol