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What is a colloid?

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Quick answer

A colloid is a mixture in which tiny particles of one substance are spread evenly through another but never settle out. Milk, fog, jelly, and whipped cream are colloids — their particles are bigger than a solution's molecules, yet too small to sink.

Key things to understand

  1. Particles are spread through a medium but don't dissolve or settle.
  2. They're larger than dissolved molecules but too small to filter out easily.
  3. Examples: milk (fat in water), fog (water in air), jelly, paint.
  4. Colloid particles scatter light (the Tyndall effect), so the mix looks cloudy.
  5. Constant random jostling keeps the particles suspended.

People also ask

How is a colloid different from a solution?
In a solution, particles dissolve completely and are invisible; in a colloid, larger particles stay suspended and scatter light, making it cloudy.
What is the Tyndall effect?
The scattering of a light beam by colloid particles — why you can see a flashlight's beam in fog or milk.
Why don't colloid particles settle?
They're so small that constant molecular bombardment keeps them jostling and suspended instead of sinking.