Ask A Scientist© Chemistry Archive

 
name       kunal
status     student
age        18

Question - Is there anything that will react with oxygen and change
color? If there is, do you have any idea on how to produce and package
it? Or how you would obtain it?
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Chemistry has been described as a collection of tricks to produce noises,
colors and odors. In my bag of tricks, I do not have anything that produces
a good color change in a short time at the gas/solid interface without a lot
of energy in or out. However, I can suggest a couple of tricks in aqueous
solution. (You have probably seen these before.) 1. Prepare a solution of
methylene blue (about 0.001%). Decolorize solution from blue to colorless
with "a pinch" of zinc metal powder (alternately: butylated hydroxytoluene,
diethylthiourea, or sodium hypophosphite may work. More possibilities:
d-Alpha tocopherol, beta-carotene or ascorbic acid (or ascorbate salt)) Let
well-stirred solution sit overnight in a closed container to fully
decolorize. You will need to try this "in the lab" to dial in how much
color and decolorizer is needed. Now the oxygen part: Take the colorless
methylene blue solution (reduced form) and oxidize it to its blue (oxidized)
state with hydrogen peroxide solution. Caution: you should be able to
change the color back and forth from colorless to blue, but if you add too
much oxidizer and it turns purple, it's purple "to stay". Consult the lab
manager prior to starting work for disposal instructions. 2. Add one mL of
phenolphthalein solution (0.1% in isopropyl alcohol or in 50/50
water/ethanol) to about 100 mL of water. This solution should be colorless
below pH 8 (8.2). If an oxygen bleach (example sodium hypochlorite) is
added to this dilute solution, the color will go momentarily to pink, due to
the pH change, then revert to colorless due to the oxidation of the color.
If the color is already set to pink with dilute alkaline solution (NaOH or
KOH, NOT (repeat NOT) NH4OH) the bleach solution will simply decolorize the
phenolphthalein solution. Note that the decolorizing of the phenolphthalein
is "permanent" A drop or two of laundry-strength bleach will probably be
sufficient. (Try this first in the lab.) Strictly speaking, this shows the
oxidizing ability of chlorine rather than oxygen. (If this works with
sodium perborate or sodium percarbonate, you are back to oxygen. These may
work in place of hydrogen peroxide in 1. also.)
Tim Spry
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Rust in our area is reddish/brown colored. There is, unfortunately, some
time involved for the color-turning to occur. Patience, though, is a
virtue.

Ric
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