Name: Renzhi W.
How come liquid can be dyed whereas gases cannot? Is it
the difference in their properties?
1. Dye molecules attach themselves to other molecules.
2. Dye molecules also have large molecular weights, and so at normal
temperatures are not
present in the gas phase.
3. Dyes need some sort of chemical bond formation
to the substance they are coloring. Atmospheric gases do not generally
provide such reactive sites for dye absorption.
As a result liquids and solids tend to be receptive to dyes while gases
Could there be some exceptions, I azm sure, but these are the trends.
When you say a liquid can be dyed I assume you mean something like using
good coloring to change the color of a liquid, such as water.
In this sense, gases can be "dyed". You just need to have a colored gas
to mix with the colorless gas. Some colored gases are Chlorine, Bromine
and Iodine vapors.
There just are not very many gases that are strongly colored and this is
because of the properties of gases. The gas molecules are very far
apart compared to molecules in liquids so each molecule has to absorb
light much more strongly to have a noticeable effect.
Also, gas molecules tend to be rather small with only a few bonds in
them. These bonds do not interact much with visible light (absorbing
visible light would impart color to the compound). Some inorganic
molecules and organic molecules with double and triple bonds do absorb
visible light but these tend to be heavy molecules with lots of
intermolecular interactions that make them liquids at room temperature.
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Update: June 2012