1. Antifreeze in Car Radiators

Ethylene glycol $HOCH_{2}CH_{2}OH$ is added to water to lower the freezing point ($\Delta Tf$ = Kf × m). A 50% by volume solution lowers the freezing point to about −37°C. Without antifreeze, water freezes at 0°C, potentially cracking the engine block.

2. Salting Roads in Winter

Spreading NaCl (or $CaCl_{2}$) on icy roads lowers the freezing point of ice. $CaCl_{2}$ (i=3) is more effective than NaCl (i=2) per mole. The salt dissolved in surface water creates a solution with a depressed freezing point, melting ice even at temperatures below 0°C.

3. Reverse Osmosis — Water Purification

Applying pressure > osmotic pressure forces water through a semipermeable membrane, leaving dissolved salts behind. Used in: desalination plants (removing sea salt), household RO filters, industrial water treatment.

4. Blood Osmolarity and Intravenous Fluids

Normal blood plasma osmolarity ≈ 285–295 mOsm/L. Intravenous solutions must be isotonic (0.9% NaCl, 5% glucose) to avoid haemolysis (hypotonic IV) or crenation (hypertonic IV). This is a direct application of osmotic pressure equality.

5. Preservation of Food (Pickling and Jam-Making)

High sugar or salt concentrations in jams and pickles create a hypertonic environment around bacteria. Water flows OUT of bacteria cells by osmosis → cells dehydrate → bacteria cannot survive. This is the principle behind preservation without refrigeration.

6. Dialysis in Kidney Disease

Haemodialysis uses a semipermeable membrane to remove waste products (urea, creatinine) from blood. The dialysis fluid is isotonic to blood to prevent net water movement, but lacks urea so urea diffuses out by concentration gradient.

7. Determination of Molar Mass of Polymers

Osmotic pressure is used to determine molar masses of polymers and proteins because even tiny concentrations give measurable pressures. Other colligative properties give immeasurably small values for large macromolecules.

8. Carbonated Beverages

Henry's law: $CO_{2}$ is dissolved under ~3.5–4 atm pressure. When the bottle is opened, pressure drops to 1 atm → $CO_{2}$ solubility falls → bubbles effervesce. Warm drinks lose carbonation faster because K_H($CO_{2}$) increases with temperature.