Osmosis

I/OSMOSIS AND DIFFUSION

Diffusion

• Definition: Diffusion is the process by which molecules spread from an area of higher concentration to an area of lower concentration until the concentrations become uniform throughout the space.

• Example: Pouring a saturated aqueous solution of potassium permanganate into water shows diffusion as the permanganate rises from the bottom layer into the water, leading to a homogeneous solution over time.

• Bilateral Process:

  • Solute molecules diffuse into the solvent.

  • Solvent molecules diffuse into the solution.

• Concentration Equalization: The driving force behind diffusion is the tendency to equalize concentration in all parts of the solution.

Osmosis

• Definition: Osmosis is a special type of diffusion involving the movement of water (solvent) through a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.

• Semipermeable Membrane: It allows the passage of solvent but restricts solute movement.

• End Result: Osmosis continues until there is equal concentration of solutes on both sides of the membrane.

Semipermeable Membrane

• Characteristics:

  • Allows certain substances to pass through while restricting others based on size, charge, or solubility.

  • Essential for biological processes like osmosis, enabling water and solute movement across cell membranes.

• Examples:

  • Natural membranes such as pig’s bladder, egg membranes, and plant cell membranes.

Demonstration of Osmosis

• Animal Bladder Experiment:

  • A thistle funnel with a semipermeable membrane contains concentrated sugar solution immersed in water; water moves into funnel, raising the solution.

• Egg Experiment:

  • De-shelled eggs placed in distilled water swell as water enters, while eggs in salt solution shrink due to water leaving the egg to balance solute concentrations.

Dialysis

• Definition: Kidney dialysis is a medical treatment that filters waste materials from the blood of patients with renal failure.

• Process: Blood is pumped through a dialysis machine, filtering it via a semipermeable membrane to remove wastes before returning it to the body.

Osmotic Pressure

• Definition: The external pressure required to prevent the flow of solvent through a semipermeable membrane from a higher to a lower concentration.

• Influence: Osmotic pressure is affected by the difference in solute concentrations - the greater the difference, the higher the osmotic pressure.

• Consequences of Absence: Leads to cell shrinking, swelling, impaired function, or tissue damage.

Modern Osmometer

• Description: An apparatus for determining osmotic pressure involving a stainless steel cell divided by a semipermeable membrane.

• Function: Measures the degree of diaphragm distortion due to osmosis, related to osmotic pressure, using a strain gauge to convert distortion into an electric current.

Types of Solutions

• Isotonic Solution: Equal solute concentration across membrane; no net movement of water.

• Hypotonic Solution: Lower solute concentration than the cell; water moves in, causing cell swelling.

• Hypertonic Solution: Higher solute concentration than the cell; water moves out, causing cell shrinkage.

Theories of Osmosis

• Molecular Sieve Theory: Membrane acts as a sieve; solvent moves from higher solute concentration to lower.

• Membrane Solution Theory: Membrane interacts chemically with water, influencing flow.

• Vapor Pressure Theory: Suggests diffusion occurs due to differences in vapor pressure between pure solvent and solution.

• "Membrane Bombardment Theory: Unequal bombardment pressure on both sides of the membrane drives osmosis.

Viscosity

• Definition: Measures a fluid's internal resistance to flow, quantifying the frictional forces between molecules.

• Effects: Higher viscosity indicates slower flow (e.g., honey), while lower viscosity signifies easier flow (e.g., water).

• Variability: Affected by temperature and pressure; heating often reduces viscosity.

Kinematic and Absolute Viscosity

• Kinematic Viscosity: Measured by fluid resistance to flow under gravity (in centistokes, CSt).

• Absolute Viscosity: Resistance to flow under controlled force (in centipoise, cP).

Viscometer

• Definition: An instrument to measure fluid viscosity through drag resistance during motion.

• Formula: Viscosity = shear stress / shear rate; shear stress is the force per area, shear rate is the velocity change.

Importance of Viscometer

• Quality Control: Essential for ensuring consistent fluid properties in production.

• Fluid Behavior: Understanding viscosity helps in engineering and fluid mechanics applications.

• Types of Fluids:

  • Newtonian fluids have constant viscosity regardless of shear rate (e.g., water).

  • Non-Newtonian fluids demonstrate variable viscosity depending on shear conditions (e.g., ketchup).

Types of Viscometer

• Capillary Viscometers: Measure viscosity by analyzing fluid flow through a narrow tube.

• Falling/Rising Ball Viscometers: Based on ball motion through fluid; drag forces us ed to calculate viscosity.

• Rotational Viscometers: Measure resistance to flow when a spindle is rotated.

Specific Viscometers

• Ostwald Viscometer: U-tube viscometer for measuring viscosity through fluid flow time.

• Suspended Level Viscometer: Modified Ostwald for higher precision in more viscous fluids.

• Falling Ball and Rising Ball Viscometers: Use principles of gravity and buoyancy to deduce viscosity based on ball motion.

Electrical Properties of Sols

• Charge: Colloidal particles carry electric charges; this prevents aggregation, providing stability.

• Double Layer: Positive and negative ions create a Helmholtz double layer, leading to zeta potential.

• Electrophoresis: Movement of charged sol particles toward electrodes under electric potential.

Coagulation and Protection

• Coagulation: Loss of charge results in particle aggregation and settling.

• Protective Action: Lyophilic sols can stabilize lyophobic sols against precipitation by forming protective coatings.

Gold Number

• Definition: Measure of a hydrophilic colloid's protective ability, indicating how much is needed to prevent lyophobic sol precipitation.

Donnan Equilibrium

• Definition: Refers to the unequal distribution of ions across a semipermeable membrane leading to concentration and electrical gradients.

Phase Rule

• Definition: A relationship that describes the equilibrium condition in heterogeneous systems affecting phase coexistence.

• Formula: F = C - P + 2; where F is degree of freedom, C is number of components, and P is number of phases.

• Types of Systems: Description of invariant, monovariant, and bivariant systems based on degrees of freedom and component interactions.

Phase Diagram

• Application: Visual representation showing conditions under which multiple phases coexist; includes areas for solids, liquids, and vapors, curves demonstrating phase transitions, and the triple point.