Neither solution nor suspension

The idea

A colloid is neither a solution nor a true suspension: its particles stay uniformly dispersed throughout the mixture, as in a solution, and, unlike suspension particles, stay dispersed over time instead of settling.

Milk and blood

We cannot see blood cells with the naked eye, yet blood can be separated into its parts by centrifugation. Milk looks the same all through, yet it is not a clear solution.

What kind of mixture is milk or blood?

• Neither a solution nor a true suspension
• A solution, because it looks uniform
• A suspension, because it is cloudy

Leave three glasses standing

Salt solution, milk, and sand in water. Let time pass and watch the particles. What does milk do?

Colloid

A colloid is neither a solution nor a true suspension. Its particles are uniformly dispersed throughout the mixture, as in a solution, but unlike a suspension they do not settle over time.

Examples of colloids: blood, milk, tomato sauce and ice cream.

Notes

A colloid is neither a solution nor a true suspension: its particles stay uniformly dispersed and do not settle. Examples: blood, milk, tomato sauce, ice cream.

Check yourself

Which of these is a colloid?

Unlike the particles of a suspension, the particles of a colloid…

Which is true of both a colloid and a solution?

Which of these is not a colloid?

• Sand in water. Its particles settle: a suspension.
• Milk — correct. Yes. Its particles stay dispersed and do not settle.
• Salt in water. A clear solution.
• settle quickly to the bottom. That is a suspension.
• are all visible to the naked eye. A colloid’s particles cannot be seen with the naked eye.
• do not settle over time — correct. Yes.
• The particles are uniformly dispersed — correct. Yes.
• The particles settle over time. Neither one settles.
• The mixture is always clear. A colloid can look cloudy, like milk.
• Tomato sauce. It is a colloid.
• Sand stirred into water — correct. It is a suspension: the sand settles.
• Ice cream. It is a colloid.