$delta_{Tb}$ = i * Kb * m. Kb = molal elevation constant = R*$Tb^2$*\frac{M_solvent}{1000*delta_H_vap}. For water: Kb = 0.512 K.kg/mol, Tb = 373 K. Physical explanation: adding non-volatile solute lowers vapour pressure, so a higher temperature is needed to make vapour pressure equal atmospheric pressure. $delta_{Tb}$ is always positive (boiling point rises). Key: Kb depends only on the solvent, not the solute. Solvents with high Kb: camphor (Kb = 5.95), acetic acid (3.07), benzene (2.53). Higher Kb means greater sensitivity for molar mass determination. For molar mass: M = (i * Kb * $w_{solute}$ * 1000) / ($delta_{Tb}$ * $w_{solvent}$). If i is unknown, the "apparent" molar mass differs from true molar mass.