Dark Coloured Bottles in Chemistry Labs

In summary, opaque bottles can prevent light from entering the bottle and this allows the chemicals to last longer.
  • #1
Bubonic Plague
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When you enter a chemistry lab, on the bench, there are some bottles containing chemicals, and some of these chemical bottles are tinted so that they have a dark brownish colour.

My chemistry teacher had told the class that the dark colour is used to prevent light from getting to the chemicals stored in the bottle, so that the chemicals will last longer. But I don't understand why.

Let's say the bottle is not tinted and clear, the light will get to the chemicals, which is common sense, and provide energy for the chemicals to decompose or react.

Now let's say the bottle is tinted, the most of the light that falls on the bottle will be absorbed by the bottle, 'cause dark colours absorb more light. And the energy absorbed from the light will then be transferred by conduction to the chemicals, cause there will be a energy gradient between the chemical and the bottle. So in the end, it's all back to square one. So how does making the bottle dark in colour actually help in anyway?

My physics is not the greatest, please point out any flaws in my physics.:smile:
 
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  • #2
In such cases, visible light (read: relatively high frequency light) is capable of making the chemical decompose. When the bottle is darkened, the light is converted to heat when it strikes the bottle. Heat, unlike light, does not cause the chemical to decompose.

It is true, however, that the bottle's walls reradiate the energy into the chemical, but mostly in the infrared spectrum (since all objects at room temperature radiate mostly in the infrared). The infrared photons do not have enough energy to activate the reaction, so the chemical stays fresh.

- Warren
 
  • #3
chroot, your explanation is IMO correct. Still I suspect this might be an urban legend... If they are so concerned about light, why not paint the bottles black? And why are there no dark plastic bottles, just white ones (AFAIK)?
 
  • #4
You may be familiar with hydrogen peroxide from the apothecary, stored in dark plastic bottles to prevent photolysis.
 
  • #5
Originally posted by arcnets
chroot, your explanation is IMO correct. Still I suspect this might be an urban legend... If they are so concerned about light, why not paint the bottles black? And why are there no dark plastic bottles, just white ones (AFAIK)?

Opaque bottles would certainly keep the light out, and sometimes that is done, with especially sensitive liquids. But then you can't tell just by looking what is the level of fluid in the bottle.

In the old days before it was pasteurized, beer came in brown bottles.

I believe specifically UV radiation is the culprit.
 
  • #6
dont forget about beer bottles!
 
  • #7
In such cases, visible light (read: relatively high frequency light) is capable of making the chemical decompose. When the bottle is darkened, the light is converted to heat when it strikes the bottle. Heat, unlike light, does not cause the chemical to decompose.

What is that special property which light has that can decompose chemicals?

It is true, however, that the bottle's walls reradiate the energy into the chemical, but mostly in the infrared spectrum (since all objects at room temperature radiate mostly in the infrared). The infrared photons do not have enough energy to activate the reaction, so the chemical stays fresh.

What about through conduction too?
 
  • #8
What is that special property which light has that can decompose chemicals?

the ability to carry energy?

in paticular, it carries the proper activation energy
 
  • #9
Originally posted by selfAdjoint
In the old days before it was pasteurized, beer came in brown bottles.

So they didn't want to let light into prevent the beer from ... fermenting? what?

is fermenting what makes beer bad so that they would want to limit fermentation?

(note: I am not old enough for beer so i wouldn't really know too much about it)

can you briefly explain how pasteurizing does the same thing to beer as preventing light from entering the beer? i mean, what's the point of keeping the light out of the beer?
 
  • #10
Bubonic Plague
What is that special property which light has that can decompose chemicals?
As I mentioned above, photolysis[b(].
 
  • #11
the ability to carry energy?
As I mentioned above, photolysis.
Heat, unlike light, does not cause the chemical to decompose.
I know that light carries with it energy, but what is so different about the energy from light and the energy from heat which is conducted or radiated to the chemical that only energy from light can cause the chemicals to decompose?

Pardon me, i just can't seem to "see" the answer.
 

1. Why are dark coloured bottles used in chemistry labs?

Dark coloured bottles are used in chemistry labs to protect light-sensitive chemicals from degradation caused by exposure to light. These bottles are usually made of amber or brown glass, which blocks out the majority of the visible light spectrum and some UV light.

2. Can I use clear bottles instead of dark coloured bottles in a chemistry lab?

No, it is not recommended to use clear bottles instead of dark coloured bottles in a chemistry lab. Clear bottles do not provide adequate protection from light and can lead to the degradation of light-sensitive chemicals, potentially affecting the accuracy and reliability of experiments.

3. Are there any chemicals that do not require dark coloured bottles?

Yes, some chemicals are not sensitive to light and do not require dark coloured bottles for storage. For example, water and some acids and bases can be stored in clear bottles without any adverse effects.

4. Do dark coloured bottles have any other benefits besides protecting light-sensitive chemicals?

Yes, dark coloured bottles also help to maintain the temperature of the chemicals inside. They act as insulators, preventing rapid temperature changes that can affect the stability and reactivity of some chemicals.

5. Can I reuse dark coloured bottles in a chemistry lab?

Yes, dark coloured bottles can be reused in a chemistry lab as long as they are properly cleaned and sterilized before each use. It is important to follow proper cleaning and sterilization procedures to prevent contamination of chemicals and experiments.

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