Solutions, Colloids, Suspensions + Colligative Properties

• This presentation covers solutions, colloids, suspensions, and colligative properties of solutions.

Solutions and Mixtures

• Homogeneous mixtures have uniform properties throughout.
• Heterogeneous mixtures have varying properties.
• Solutions are homogenous mixtures that do not separate and cannot be separated by filtration.
• Solutions are transparent, except for solid solutions.
• Distillation and chromatography can separate the components of solutions.
• Mixing salt in water and metal alloys are examples of solutions.

Factors Affecting Solubility

• Henry's law dictates that the amount of gas dissolving in a liquid at a set temperature is directly proportional to the gas's partial pressure above the liquid.
• Gas solubility rises with increased pressure above the liquid.
• Most solids dissolve better in hot solvents, while gas solubility in water decreases as temperature increases.

Factors Affecting Gas Solubility; Hyperbaric Oxygen Therapy

• Hyperbaric Oxygen Therapy uses pure oxygen to treat carbon monoxide poisoning by directly dissolving oxygen in the bloodstream, bypassing normal hemoglobin uptake.

Factors Affecting Solution Formation Rate

• A solute's state of subdivision influences solution formation; crushed aspirin dissolves faster than a whole one.
• Agitation speeds up dissolution by dispersing particles.
• Elevated temperature accelerates solution formation.

Solubility Rules

• Substances with similar polarity tend to dissolve each other.
• Solubility rules are available for ionic compounds.

Colloids

• Colloids, also known as colloidal dispersions or systems, are stable mixtures.
• Colloids have a large surface area and solute particles ranging from 1 to 1000 nm.
• Colloids exhibit the Tyndall effect, scattering light when viewed at a right angle.
• Colloidal systems can exist in gas, liquid, or solid phases.
• Emulsions are colloidal systems of immiscible or partially miscible liquids, formed with emulsifying agents like egg yolk in mayonnaise or casein in milk.
• Sols are solid dispersed in a liquid.
• Emulsions are liquid dispersed in a liquid.
• Foams are gas dispersed in a liquid.
• Solid Sols are solid dispersed in a solid.
• Solid Emulsions are liquid dispersed in a solid.
• Solid Foams are gas dispersed in a solid.
• Solid Aerosols are solid dispersed in a gas.
• Liquid Aerosols are liquid dispersed in a gas.

Suspensions

• Suspensions are unstable mixtures with particles larger than 1000 nm that separate into phases.

Colligative Properties of Solutions

• Colligative properties are physical properties of solutions dependent on the number of solute particles, not their identity.
• Vapor-pressure lowering, boiling-point elevation, freezing-point depression, and osmotic pressure are examples of colligative properties.
• Boiling point is inversely related to vapor pressure; a drop in vapor pressure raises the boiling point.
• Freezing point decreases in the presence of a solute.

Vapor Pressure Lowering

• Adding a solute reduces vapor pressure compared to a pure solvent.

Boiling Point Elevation

• Boiling point elevation is the increase in boiling point when a nonvolatile solute is added.
• A solute reduces a solvent's vapor pressure, lowering its freezing point but elevating its boiling point.

Practical Applications of Colligative Properties

• Antifreeze, typically ethylene glycol, in car radiators prevents overheating and freezing by lowering vapor pressure and freezing point.
• Salt (NaCl or CaCl2) is used to lower the freezing point of water on roads and sidewalks during winter.
• Salt is added to ice when making ice cream to lower the freezing point of the water to get the ice cream base colder than 0C.

Osmotic Pressure

• Osmotic pressure is the force needed to prevent solvent flow through a semi-permeable membrane into a solution.
• This pressure is proportional to the solution's concentration at a constant temperature and relies on the number, not the nature, of dissolved particles.
• The greater the concentration difference between separate solutions, the greater the magnitude of osmotic pressure.

Osmosis

• Osmosis is the flow of solvent through a semipermeable membrane from a dilute to a concentrated solution.
• Water moves from areas of lower solute concentration to higher solute concentration during osmosis.

Dialysis

• Dialysis uses a semipermeable membrane to allow passage of solvents, dissolved ions, and small molecules, while blocking colloidal-sized particles and large molecules.
• Many plant and animal membranes act as dialyzing membranes.
• During dialysis, ions move from higher to lower concentration regions.

Colligative Properties Calculations

• Formula for Molality (m) = moles of solute (mol) / mass of solvent (kg).

Van't Hoff factor (i):

• the actual number of particles in soln after dissociation/mole of solute
• Strong electrolytes (ionic compounds) i = 1
• Nonelectrolytes i = 1
• Weak electrolytes (weak acids and bases) 1 < i < 2
• Example is shown using Na2SO4 showing an example how the number of particles is obtained in the equation.
• Colligative properties are the lowering of vapor pressure, the increase of boiling-point, the decrease of freezing-point and the osmotic pressure.
• Hypotonic solutions have a lower osmotic pressure that cells, so the cells will burst.
• Hypertonic solutions have a higher osmotic pressure that cells, so the cells will shrink.
• Isotonic solutions are the same osmotic pressure, so there is no change in cell sixe.
• Osmolarity = morality x i (the number of particles).