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Osmosis Overview

• Definition: Osmosis is the movement of water molecules across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration until equilibrium is reached.

• Examples in Life: Osmosis occurs in various processes in nature and human activities.

  • Control of water levels in plants and animals.

  • Importance in food preservation.

Semi-Permeable Membrane Example

• Two Containers:

  • Separated by a semi-permeable membrane.

  • Only water molecules can pass; solutes cannot.

• Starch Solutions:

  • Container A: 4% starch solution.

  • Container B: 10% starch solution.

• Water Flow Direction:

  • Water will flow from the 4% (lower concentration) to the 10% (higher concentration) to equalize concentrations.

• Equilibrium:

  • Water continues to flow until concentrations are equal; at which point, flow rates are equal and levels stabilize.

Osmotic Pressure

• Definition: The pressure required to stop the flow of water through the semi-permeable membrane when solvent concentration is unequal.

• Cause of Osmotic Pressure: Increased solute concentration leads to higher liquid height and pressure in that solution.

• Formula:

  • Osmotic pressure (π) is described by the equation: π = MRT, where:

    • M = molarity of the solution

    • R = universal gas constant (0.08206 L•atm/K•mol)

    • T = temperature in Kelvin.

• Units: Atmospheric pressure (atm), millimeters of mercury (mmHg), torr.

Example Calculation

• D5W Solution: 5% dextrose solution in an osmometer.

  • Density: 1 g/mL; surroundings are distilled water (considered zero concentration).

• Expected Osmotic Pressure: To calculate, we switch from mass percent to molarity:

  • 5 grams of dextrose in 100 mL solution translates to molarity using the molar mass (180.16 g/mol).

  • Molarity calculation yields 0.278 mol/L.

  • Substitute into osmotic pressure formula: π = 0.278 mol/L × 0.08206 L•atm/K•mol × 298 K = X atm.

Reverse Osmosis

• Importance: A method for obtaining fresh, drinkable water from saline or contaminated sources.

• Process:

  • Liquid is pressured to flow from more concentrated (saltwater) to less concentrated (freshwater) through a membrane, reversing natural osmosis.

• Cost: Reverse osmosis is resource-intensive and often expensive.

Osmosis in Medicine

• Dialysis: Critical in treating individuals with kidney failure.

  • Types:

    1. Peritoneal Dialysis: Utilizes the peritoneal membrane to filter waste; involves fluid exchange in the abdominal cavity.

    2. Hemodialysis: Blood is filtered outside the body and returned, typically requiring three sessions a week for hours.

• Importance: Maintains metabolic balance by removing toxins and adding necessary substances to the blood.

Osmosis and Cell Behavior

• Hypertonic Solutions: Higher solute concentration outside the cell results in water flowing out, causing cell shrinkage.

• Hypotonic Solutions: Lower solute concentration outside the cell leads to water entering the cell, potentially causing lysis (bursting).

• Isotonic Solutions: Equal concentrations inside and outside the cell maintain cell integrity; essential for IV solutions (e.g., 0.9% saline).

Conclusion

• Understanding osmosis and its implications is vital for multiple disciplines, including biology, medicine, and environmental science. Correct application in practical scenarios, such as medical treatments and cooking, is crucial.