colligative properties pt 2

Freezing point depression in plain words

Dissolved particles increase solution entropy, making the liquid state more favorable; the freezing point drops relative to the pure solvent.

Why ΔTf depends on molality and i (conceptually)

Molality measures particle concentration independent of temperature/volume changes, and i counts how many particles result from each formula unit; more particles → more disruption of freezing.

Boiling point elevation in plain words

Because solute lowers vapor pressure at every temperature, the liquid must be heated more to reach atmospheric pressure; the boiling point rises.

Shared logic behind ΔTf and ΔTb

Both arise from the same dilution/entropy effect: more particles make the liquid phase relatively more favorable over solid (freezing ↓) and less volatile over gas (boiling ↑).

Osmosis in one sentence

Solvent passes through a semipermeable membrane from the less concentrated side to the more concentrated side until equilibrium is reached.

What stops osmosis at equilibrium?

The hydrostatic pressure buildup on the concentrated side balances the driving force; this opposing pressure is the osmotic pressure Π.

Concept link: why Π tracks concentration and i

More solute particles create a larger chemical potential difference for the solvent, so a larger external pressure is required to stop flow.

Isotonic vs hypotonic vs hypertonic (connections)

Isotonic: equal Π. Hypotonic: lower Π (more dilute). Hypertonic: higher Π (more concentrated). Water flows from hypotonic → hypertonic.

Reverse osmosis, conceptually

Applying external pressure greater than Π pushes solvent back through the membrane, leaving solute behind (basis of water purification).

Choosing which solution boils higher or freezes lower without math

Compare effective particle concentration i·m (or i·M): larger i·m → bigger ΔTb and ΔTf (boil higher, freeze lower).

Why molality (m) is favored in these relations

It uses solvent mass, not volume, so it doesn't change with temperature; that keeps the particle concentration definition stable.

Grand connection across all colligative properties

All four—vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure—reflect how particle number changes the solvent's chemical potential and phase preferences.

Kf

freezing point depression constant

What does a high Kf correlate with?

Low Freezing point depression

What is Fp

The actual freezing point

Low i means? (FP)

High Freezing point depression

What is Kb

Boiling point elevation constant

low kb?

low boiling point increase

high i (Kb)

high boiling point increase

inc concentration

inc boiling point, inc osmotic pressure, dec freezing point, dec vapor pressure