Answer: 214 g/mol
Explanation:
Formula used for Elevation in boiling point :
[tex]\Delta T_b=k_b\times m[/tex]
or,
[tex]T_{solution}-T_{solvent}=k_b\times \frac{\text{Mass of solute}}{\text {Molar mass of solute}\times \text{ Mass of solvent in Kg}}[/tex]
where,
[tex]T_b[/tex] = change in boiling point =[tex](81.5-76.8)^0C=4.7^0C[/tex]
[tex]k_b[/tex] = boiling point constant =[tex]5.02^0C/m[/tex]
m = molality = [tex]\frac{5g}{\text{ Molar mass of solute}}\times 0.025kg[/tex]
[tex]4.7=5.02\times \frac{5g}{\text {Molar mass of solute}\times 0.025kg}[/tex]
[tex]{\text {Molar mass of solute}}=214g/mol[/tex]
Thus molar mass of solute is 214 g/mol.
