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Why does concentrated nitric acid turn yellow on exposure to sunlight?
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Mary Clayton
Why does concentrated nitric acid turn yellow on exposure to sunlight?
Nitric acid, upon exposure to light and heat, will spontaneously decompose to nitrogen dioxide, water, and oxygen, creating the brownish-yellow color. It's not actually completely decomposing unless you leave it for a long time (in which case it will eventually turn red), but there's enough dissolved nitrogen dioxide, which is what imparts the color, to give it a distinct hue.
The chemical equation is: [math]4 HNO_3
ightarrow 2 H_2O + 4 NO_2 + O_2[/math]
Most of the gas that escapes from nitric acid that's been exposed to air is nitrogen dioxide, hence the names "red fuming" nitric acid to describe nitric acid at high concentration that has been exposed to light.
Nitric acid, upon exposure to light and heat, will spontaneously decompose to nitrogen dioxide, water, and oxygen, creating the brownish-yellow color. It's not actually completely decomposing unless you leave it for a long time (in which case it will eventually turn red), but there's enough dissolved nitrogen dioxide, which is what imparts the color, to give it a distinct hue.
The chemical equation is: [math]4 HNO_3 ightarrow 2 H_2O + 4 NO_2 + O_2[/math]
Most of the gas that escapes from nitric acid that's been exposed to air is nitrogen dioxide, hence the names "red fuming" nitric acid to describe nitric acid at high concentration that has been exposed to light.
You will get a certain amount of the acid decomposing into nitrogen dioxide & water when exposed to heat or sunlight. NO2 is a yellow-brown liquid below 21.2°C, so will give the acid solution a yellow tinge (above its boiling point, it’ll come out of solution as a red-brown gas).
You will get a certain amount of the acid decomposing into nitrogen dioxide & water when exposed to heat or sunlight. NO2 is a yellow-brown liquid below 21.2°C, so will give the acid solution a yellow tinge (above its boiling point, it’ll come out of solution as a red-brown gas).
Nitric acid, upon exposure to light and heat, will spontaneously decompose to nitrogen dioxide, water, and oxygen, creating the brownish-yellow color. It's not actually completely decomposing unless you leave it for a long time (in which case it will eventually turn red), but there's enough dissolved nitrogen dioxide, which is what imparts the color, to give it a distinct hue.
The chemical equation is:
[math]4 HNO_3 ightarrow 2 H_2O + 4 NO_2 + O_2[/math]
Most of the gas that escapes from nitric acid that's been exposed to air is nitrogen dioxide, hence the names "red fuming" nitric acid to describe nitric acid at high concentration that has been exposed to light.
Nitric acid, upon exposure to light and heat, will spontaneously decompose to nitrogen dioxide, water, and oxygen, creating the brownish-yellow color. It's not actually completely decomposing unless you leave it for a long time (in which case it will eventually turn red), but there's enough dissolved nitrogen dioxide, which is what imparts the color, to give it a distinct hue.
The chemical equation is:
[math]4 HNO_3 ightarrow 2 H_2O + 4 NO_2 + O_2[/math]
Most of the gas that escapes from nitric acid that's been exposed to air is nitrogen dioxide, hence the names "red fuming" nitric acid to describe nitric acid at high concentration that has been exposed to light.
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You will get a certain amount of the acid decomposing into nitrogen dioxide & water when exposed to heat or sunlight. NO2 is a yellow-brown liquid below 21.2°C, so will give the acid solution a yellow tinge (above its boiling point, it’ll come out of solution as a red-brown gas).
You will get a certain amount of the acid decomposing into nitrogen dioxide & water when exposed to heat or sunlight. NO2 is a yellow-brown liquid below 21.2°C, so will give the acid solution a yellow tinge (above its boiling point, it’ll come out of solution as a red-brown gas).
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