Intermediate Topic 314 of 1102 States of Matter & Solutions
Colloids
Mixtures with particles of 1 to 1000 nm that scatter light but do not settle.
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In-depth explanation of Colloids
A colloid is a mixture in which dispersed particles about 1 to 1000 nm in size are spread throughout a dispersion medium, but they do not settle out under gravity. The particles are too small to be seen with an ordinary microscope, yet they are large enough to scatter light, and they cannot pass through ordinary filter paper. Colloids are classified by the phases involved, such as sol, gel, emulsion, foam and aerosol. Stability comes from electrical charges on the particle surfaces, which cause them to repel one another. Milk, fog, paint and blood plasma are common examples.
Going deeper: Colloids
Key ideas: Size range is 1 to 1000 nm. Types: sol (solid in liquid, like paint), gel (liquid in solid, like jelly), emulsion (liquid in liquid, like milk), foam (gas in liquid, like whipped cream), aerosol (solid or liquid in gas, like smoke or fog). Lyophilic colloids are solvent loving and stable; lyophobic need stabilizers. Purified by dialysis.
Common mistakes and connections: Students assume colloids are just fine suspensions; they are stable and do not settle, and pass through ordinary filter paper but not through a semipermeable membrane. Another error is that a colloid is a compound. Colloids can be separated by ultracentrifugation. Links to Tyndall effect, Brownian motion, coagulation and emulsions.
Visualization of Colloids
Colloids hold dispersed particles of 1 to 1000 nm that stay suspended: smoke, fog, milk and paint, between true solutions and suspensions. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Milk, fog and paint are colloids, and each stays evenly mixed without settling for a long period.
Frequently asked questions about Colloids
What is Colloids?
Mixtures with particles of 1 to 1000 nm that scatter light but do not settle.
Is Colloids a beginner, intermediate or advanced topic?
Colloids is a intermediate topic in States of Matter & Solutions. It builds on the vocabulary of beginner topics in this area.
What should I learn before Colloids?
Study these earlier topics in States of Matter & Solutions first: Reverse Osmosis, van't Hoff Factor, Abnormal Molar Mass.
What comes after Colloids?
The next topics in States of Matter & Solutions are Tyndall Effect and Brownian Motion.
Can I practise Colloids with quizzes?
Yes. The interactive lesson includes a self-check question on Colloids, and the States of Matter & Solutions quiz draws on every topic in this area.
Where Colloids fits in States of Matter & Solutions
Colloids is topic 95 of 109 in States of Matter & Solutions.