Question

Determine the change in boiling point for 397.7 g of carbon disulfide (Kb = 2.34°C kg/mol) if 35.0 g of a nonvolatile, nonionizing compound is dissolved in it. The molar mass of the compound is 70.0 g/mol and the boiling point of the pure carbon disulfide is 46.2°C.

Answer 1

Answer: The change in boiling point for 397.7 g of carbon disulfide (Kb = 2.34°C kg/mol) if 35.0 g of a nonvolatile, nonionizing compound is dissolved in it is $2.9^0C$

Explanation:

Elevation in boiling point:

$T_b-T^o_b=i\times k_b\times \frac{w_2\times 1000}{M_2\times w_1}$

where,

$T_b$ = boiling point of solution = ?

$T^o_b$ = boiling point of pure carbon disulfide= $46.2^oC$

$k_b$ = boiling point constant  =$2.34^0Ckg/mol$

m = molality

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

$w_2$ = mass of solute = 35.0 g

$w_1$ = mass of solvent (carbon disulphide) = 397.7 g

$M_2$ = molar mass of solute = 70.0 g/mol

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

$(T_b-46.2)^oC=1\times (2.34^oC/m)\times \frac{(35.0g)\times 1000}{70.0\times (397.7g)}$

$T_b=49.1^0C$

Therefore, the change in boiling point is $(49.1-46.2)^oC=2.9^0C$