Is there an agent that changes colour when exposed to air?

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Many compounds change colour when exposed to 'air', however, this is usually due to the presence of either water or oxygen, rather than 'air'.

To give a few examples:

*when distilling a solvent such as THF over sodium/potassium, benzophenone is used as an indicator. In the absence of air, the indicator leaves the solution a deep purple colour, however if an excess of air is present, the indicator turns a clear/brown colour.

*drierite is an indicator often used in inert gas drying tubes. In its dry form, it is either deep blue or orange, however when wet it turns white/pale orange.

Several other indicators exist, however its worth noting that air is merely a mixture of multiple things, and as such any indicator will indicate for a specific component of air rather than air as a whole- with water and oxygen being the most common things to indicate for.

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Edward brown
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Edward brown

Updated on August 01, 2022

Comments

  • Edward brown
    Edward brown over 1 year

    And if so, does it come in a liquid form? Thank you for your time

    • ron
      ron about 8 years
      Need it be reversible?
    • Mithoron
      Mithoron about 8 years
      It's too broad, there are lots of things that react with oxygen, changing color.