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Name: Renzhi W.
Status: student
Age: 15
Location: N/A
Country: N/A
Date: 7/12/2004


Question:
How come liquid can be dyed whereas gases cannot? Is it the difference in their properties?


Replies:
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 are not.

Could there be some exceptions, I azm sure, but these are the trends.

Vince Calder


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.

Greg Bradburn



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