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A bonus question would be, if so, why? Is it because it decomposes and hence the expiry date is calculated out?

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  • $\begingroup$ Whether manufacturers put one on is a separate question to whether all chemicals will decay in some way when stored. Some will expire quickly, others slowly and other not at all. And some will last indefinitely if stored appropriately but only for a short time if not. There is no general answer. $\endgroup$ – matt_black Jul 8 '18 at 21:38
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They do indeed. It could be for different reasons:

  • A chemical might undergo chemical changes due to different storage conditions: it could react with other chemicals present in the air or in the environment. This could change its nature (reaction to create other compounds), properties and/or purity.
  • A chemical might undergo physical changes as well: the temperature and pressure vary, as well as other conditions like humidity, light, electromagnetic fields. This could change it as stated above.
  • Certain chemicals are simply unstable and decay or degradate over time to something else, without the need of externals input / changes. This could affect the chemical as stated above.
  • Certain chemical suffers transpiration losses.
  • Human factors, like contaminations, spillings, loose caps, etc.

However, it might be noticed that these reasons could be divided to produce two different dates: shelf life vs expiration date.

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    $\begingroup$ And even if chemicals don't have an expiry date the manufacturer still prints one on the box. That's because the date serves as the batch number. $\endgroup$ – Abel Friedman Nov 27 '14 at 0:41
  • $\begingroup$ @AbelFriedman so the expiry date its more for stock taking than anything else? $\endgroup$ – Nick Nov 27 '14 at 0:48
  • $\begingroup$ Not really, it depends on the nature of the chemical. $\endgroup$ – entropid Nov 27 '14 at 0:51
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    $\begingroup$ Even alcohol has expiry data... Anyway, it is a bad practice to keep old chemicals around ad infinitum. I happened to work in a lab with plenty of ancient chemicals around. Even with the stable one after a while the labels peels off, the lid get stuck, etc.. $\endgroup$ – Greg Nov 27 '14 at 1:13
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    $\begingroup$ I found an old bottle of magnesium chloride in one of the places I worked. The problem was that it had absorbed so much water from the air, it was all in solution when I found it. $\endgroup$ – LDC3 Nov 27 '14 at 1:32

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