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Ch.4 - Reactions in Aqueous Solution
Chapter 4, Problem 13.85b

(b) In the 1850s, Michael Faraday prepared ruby-red
colloids of gold nanoparticles in water that are still stable
today. These brightly colored colloids look like solutions.
What experiment(s) could you do to determine whether a
given colored preparation is a solution or colloid?

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Colloids vs. Solutions

Colloids are mixtures where tiny particles are dispersed throughout a medium, but they do not settle out over time, unlike solutions where solute particles are completely dissolved. In colloids, the particle size is typically between 1 nanometer and 1 micrometer, which gives them unique optical properties, such as scattering light, leading to their characteristic colors.
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Tyndall Effect

The Tyndall Effect is the scattering of light by particles in a colloid or in very fine suspensions. This phenomenon can be used to distinguish between a colloid and a true solution; if a beam of light passes through the mixture and is visible, it indicates the presence of colloidal particles, whereas a true solution would not scatter light and would appear clear.
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Stability of Colloids

Colloids can remain stable over time due to the balance of attractive and repulsive forces between the dispersed particles. Factors such as particle size, charge, and the presence of stabilizing agents (like surfactants) can affect this stability. Understanding these factors is crucial for designing experiments to test the nature of the preparation, as stability can influence the behavior of the colloid.
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