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Four colligative properties depend only on number of solute particles: (1) RLVP: delta_P/P_std = ix_solute (non-volatile solutes only). (2) Boiling point elevation: delta_Tb = iKbm. (3) Freezing point depression: delta_Tf = iKfm. (4) Osmotic pressure: pi = iMRT. Key constants for water: Kb = 0.512 K.kg/mol, Kf = 1.86 K.kg/mol. Origin of constants: Kb = RTb^2M_solvent/(1000delta_H_vap), Kf = RTf^2M_solvent/(1000delta_H_fus). Kf > Kb because delta_H_fus < delta_H_vap. Solvents with high Kf: camphor (40), naphthalene (6.94), benzene (5.12). Molar mass determination: M = Kfw21000/(delta_Tfw1) or M = wRT/(piV). Osmotic pressure is most sensitive — preferred for macromolecules. The van't Hoff factor i connects all four properties to electrolyte behaviour. For non-electrolytes: i = 1. For dissociation into n ions: i = 1 + (n-1)alpha. For association of n molecules: i = 1 - alpha(1-1/n). Abnormal molar mass: M_apparent = M_actual/i. Dissociation (i>1) gives M_apparent < M_actual. Association (i<1) gives M_apparent > M_actual. When multiple solutes are present: delta_Tf = Kf * sum(i_j * m_j). All colligative property formulas require correct i for accurate results.