Understanding Emulsions and Colloids

Emulsions

• Margarine, cold cream, and medicated ointments are examples of emulsions, consisting of two immiscible liquids.
• Emulsions are colloidal systems where one liquid is dispersed in another in small droplets.
• Some emulsions require shaking before use as suspended particles can settle over time.

Colloids

• Colloids appear homogeneous but are actually heterogeneous mixtures.
• Particle sizes range from 10^-9 m to 10^-6 m.
• Colloids do not separate upon standing and are not separable by filtration.
• They scatter light, demonstrating the Tyndall effect.

Types of Colloids & Examples

• Solid in solid: Solid sol; examples include colored glass and gemstones.
• Liquid in gas: Aerosols; examples are smoke and dust.
• Gas in liquid: Gels; examples include cheese, butter, and jellies.
• Solid in liquid: Emulsions; examples are milk and hair cream.
• Liquid in gas: Aerosols; includes fog, mist, and insecticide sprays.
• Gas in solid: Solid sol; example is pumice stone and foam rubber.
• Gas in gas: Foam; includes whipped cream and soap lather.

Suspensions

• Suspensions are heterogeneous mixtures with particle sizes larger than 10^-6 m.
• Particles in suspensions eventually settle down over time.
• Suspensions can be separated by filtration and may either scatter light or appear opaque.

Key Characteristics

• Colloids exhibit Brownian motion, indicating random movement of particles within.
• The dispersion medium acts as the solvent, while solute forms a solution.

Review Questions

• Arrange true solutions and dispersed particles by their properties.
• Explain the stability of colloids compared to the settling of suspension particles.
• Smoke and fog are classified as colloids.
• Identify the dispersion medium in whipped cream on a hot day.
• Determine if an unknown solution is an emulsion or a suspension by heating.
• True solutions do not show the Tyndall effect.
• Use filtration to characterize an unknown solution as a suspension.
• Increasing the temperature accelerates gas rates due to increased molecular movement.
• A lake provides a more comfortable experience than a swimming pool on a hot day.
• Provide an example of both a colloid and a suspension.

Separating Techniques

• Mixtures consist of two or more substances that are physically combined, not chemically united.
• Separation techniques exploit differences in properties to isolate components from a mixture.