Solution of copper sulphate is deep blue. When diluted with warm water, changes to paler blue. Explain this in terms of the particle theory of matter?A concentrated solution of copper (II)...

Solution of copper sulphate is deep blue. When diluted with warm water, changes to paler blue. Explain this in terms of the particle theory of matter?

A concentrated solution of copper (II) sulphate is deep blue. When you dilute it with warm water, it becomes a paler blue. How can you explain this in terms of the particle theory of matter?

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pacorz | High School Teacher | (Level 3) Educator

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When white light shines through a solution or other transparent material, the wavelengths that are NOT absorbed are the ones that you see -  in the case of Copper II Sulphate, the blue wavelengths are being both transmitted and reflected, while the other colors (primarily red wavelengths in this case) are absorbed by the solution.This absorption occurs because some of the valence electrons (D block in the case of transition metals like copper) are able to absorb specific wavelengths of light which kick them to a higher energy state. As you dilute the solution, these ions are spread farther apart, and more light passes through without encountering a copper ion; the additional  light transmitted is of all different wavelengths, thus adding up to "white" as we perceive it visually.

The Beer-Lambert Law states the mathematical relationship among absorption, transmission, and solution concentration. Basically it states that the "optical density" of a solution is directly proportional to its concentration. I have included a link to a photometry site here that gives the Law and its mathematical derivation if you need them.

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