Answer : The molar mass of unknown compound is 128.22 g/mole
Explanation :
Mass of unknown compound = 9.72 g
Mass of solvent = 50.0 g
Formula used :
[tex]\Delta T_b=i\times K_b\times m\\\\T_2-T_1=i\times K_b\times\frac{\text{Mass of unknown compound}}{\text{Molar mass of unknown compound}\times \text{Mass of solvent in Kg}}[/tex]
where,
[tex]\Delta T_b[/tex] = elevation in boiling point
[tex]T_1[/tex] = temperature of solvent = [tex]80.7^oC=273+80.7=353.7K[/tex]
[tex]T_2[/tex] = temperature of solution = [tex]84.93^oC=273+84.93=357.93K[/tex]
i = Van't Hoff factor = 1 (for non-electrolyte)
[tex]K_f[/tex] = boiling point constant for solvent = 2.79 K/m
m = molality
Now put all the given values in this formula, we get:
[tex](357.93-353.7)K=1\times (2.79K/m)\times \frac{9.72g\times 1000}{\text{Molar mass of unknown compound}\times 50.0g}[/tex]
[tex]\text{Molar mass of unknown compound}=128.22g/mole[/tex]
Therefore, the molar mass of unknown compound is 128.22 g/mole
