Solutions

Dispersions

  • Mixtures made of two or more substances – think of it as a microscopic party where everyone tries to mingle!

  • Components:

    • Dispersed phase (disperso) = particles being spread (the party guests).

    • Dispersing phase / medium (dispergente) = substance that conducts the spreading (the party host, making sure everyone gets around).

Classification by Particle Diameter

  • Solution

    • Particle diameter <1\,\text{nm} (molecular or ionic scale). These particles are so tiny, they're basically invisible ninjas, sneaking through without scattering even a single ray of light. Totally homogeneous; does not scatter light.

  • Colloid

    • 1\,\text{nm} \leq \text{diameter} \leq 1000\,\text{nm} (molecular aggregates/large molecules). These are the "just right" particles – not too small to be invisible, not too big to be obvious. Heterogeneous (but looks homogeneous); scatters light (hello, Tyndall effect!).

  • Suspension

    • >1000\,\text{nm} (visible with naked eye). These are the chunky ones, too big to hide, and eventually, they get tired and settle down at the bottom. Heterogeneous; scatters light; opaque; settles over time.

Characteristic Properties of Colloids
1. Tyndall Effect

  • Definition: Scattering of a light beam by colloidal particles. Think of it as colloids acting like tiny disco balls, revealing the path of light – perfect for a science rave! Enables visualization of the light path in a medium (e.g., head-lights in fog, or when you see dust shimmering in a sunbeam inside a cinema – it's like the air is saying 'Look at me!'). Requires particles large enough to reflect/scatter light but still below the limit of visibility – they're show-offs, but not too much.

2. Brownian Motion

  • Continuous, irregular, zig-zag motion of colloidal particles suspended in a fluid (liquid or gas). Picture these particles as perpetually confused toddlers, bouncing off everything in sight, powered by incessant, random bombardment by faster-moving solvent molecules. This non-stop dance prevents them from ever settling down and keeps the whole dispersion nice and stable – no lazy particles here!

Main Types of Colloidal Systems (by phase combination)

Dispersed Phase

Dispersing Medium

Name

Example

Liquid

Gas

Liquid Aerosol

Fog, Clouds

Solid

Gas

Solid Aerosol

Smoke, Dust

Gas

Liquid

Foam

Whipped Cream, Shaving Cream

Liquid

Liquid

Emulsion

Milk, Mayonnaise

Solid

Liquid

Sol

Paint, Ink

Gas

Solid

Solid Foam

Pumice Stone, Styrofoam

Liquid

Solid

Gel

Jelly, Cheese

Solid

Solid

Solid Sol

Some Colored Glass, Alloys

Supplementary notes:

  • "Study of the aerosols" highlights environmental & health