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Asked by meg123 to Amy, Karen, Sarah, Vijay, Will on 19 Jun 2012.
Question: How does an envelope fastening become sticky when you lick it?
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Karen Reed answered on 19 Jun 2012:
I think this is a more chemistry related question so will will probably answer it better, but I think its becuase the presence of water (from the saliver when you lick it) alters the chemical structure of the glue compounds to make them more sticky and capable of making new bonds with other things
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Sarah Martin answered on 19 Jun 2012:
Hi meg!
The glue on the envelope flap is usually a gum. A typical natural gum is gum arabic, derived from a substance produced by the acacia tree. Synthetic gums are often derived from dextrans, which are produced by the fermentation of sugar. They are dried on the envelope, and only become sticky when hydrated with water, so all you have to do is wet it a little.
🙂 Sarah
Comments
meg123 commented on :
So you dont need to lick it really sarah? Why does it taste so bad sarah?
Sarah commented on :
No, you can also use a wee damp sponge! The taste is unusual, isn’t it? I guess we don’t often taste glue, and lots of our taste buds are at the tip of our tongue, so that won’t help…
Have you tried the freezing salty water experiment yet? How did it go? 🙂
meg123 commented on :
Yes, i tryed it and the saltly water ice cubes did not freeze but the normal ones did! Why did this happen does salty water have a lower freezing point?