What Does Hygroscopic Mean?


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Robin Burden answered
A hygroscopic substance is one that is able pull water molecules in from its surrounding environment - a bit like a sponge.

Many substances that we use in our daily life can be described as hygroscopic, including sugar!

What is Hygroscopy?
Anything that is able to attract and retain water molecules can be described as hygroscopic.

If you've ever accidentally splashed some water into a sugar bowl when making yourself a cup of tea, you may have noticed that the water doesn't trickle to the bottom of the bowl - instead, it gets absorbed by the sugar.

Absorption is the most common form of hygroscopy, although another method called adsorption is also possible.

All the following substances can be said to have hygroscopic properties:

  • Honey
  • Ethanol
  • Methanol
  • Crystal Meth (Methamphetamine)
Interestingly, sodium chloride (the chemical formula for salt) is not hygroscopic.

However, if you pour water into table salt, it may become absorbed due to the presence of hygroscopic elements like magnesium (or other impurities).

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