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Q & A: Chemistry of Food!

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Most recent answer: 10/22/2007
Q:
Is milk, mayonnaise, and jello a solid liquid or a gas?
- Alex Mongoon (age 16)
Second Baptist School, Houston, TX United States
A:
These substances are known collectively as colloids. Colloids are particles suspended in solvent that are only about 1 nanometer to 1 micrometer in size. The sizes of the particles are smaller than the wavelength of light making it so the material appears uniform. However, you can't see through milk or mayonaise because so much light scatters off the suspended particles. The particles are in constant motion so they do not settle out and they may be electrically charged so electrostatic repulsion keeps them from aggregating. There are different types of colloids. Milk and mayonnaise are both emulsions which are liquid in liquid colloids. Jello is a connected web of protein in liquid, a form of gel colloid.

Milk is a liquid, just as you would think. You can see that jello, for example, is neither a solid nor a liquid. The standard categories (solid, liquid, and gas) don't come close to covering all the possible states of matter.

(published on 10/22/2007)

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