Solutions · Colligative Properties

Colligative Properties & Osmosis

Solvent slips through the semipermeable membrane into the solution, raising the column until its pressure — the osmotic pressure — stops the flow. These effects depend only on the number of dissolved particles, not what they are: that is why the van't Hoff factor i matters so much for salts.

● solvent (crosses membrane) ● solute particles (blocked) dashed line = semipermeable membrane

Solution

Concentration c 0.50 mol/L
Temperature T 300 K

Solute — particles per formula unit

A non-electrolyte like glucose stays as whole molecules — 1 particle each. Colligative effects scale with i × c.

12.3 atm
osmotic pressure π = i·c·R·T
0.50
effective mol/L (i·c)
0.26
ΔTb boiling ↑ (°C)
100.3
boils at (°C)
−0.9
freezes at (°C)
ΔTb = i·Kb·m ΔTf = i·Kf·m

Try this

Same concentration, different i: keep c fixed and switch glucose → CaCl₂. Three ions per formula unit triple the particle count, so π, boiling-point rise and freezing-point drop all jump — the solute's identity only matters through how many particles it releases.