Question

Student prepares a 0.207 g sample of the nonvolatile solute caryophyllene by dissolving the substance in 1.00 g of chloroform (Kb = 3.63C/m). The boiling point of chloroform increases by 3.68C. Determine the molar mass (g/mol) of caryophyllene?

Answer 1

Answer: 204.2 g/mol

Explanation:

Elevation in boiling point is given by:

$\Delta T_b=k_b\times m$

$\Delta T_b$ =  Elevation in boiling point =  $3.68^0C/m$

$k_b$ = boiling point constant  = $3.63^0C/m$

m = molality

$Molality=\frac{n\times 1000}{W_s}$

where,

n = moles of solute = $\text {given mass}{\text {molar mass}}=\frac{0.207}{M}$

 $W_s$ = weight of solvent in g  = 1g

Molality =$\frac{0.207\times 1000}{M\times 1g}$

Putting in the values we get,

$3.68=3.63\times \frac{0.207\times 1000}{M\times 1g}$

$M=204.2g/mol$

The molar mass of caryophyllene is 204.2 g/mol.