Ask A Scientist Chemistry Archive

  
name         Lauren H.
status       student
age          13
    
Question -   If you put a gummy bear in water and let it sit there for
about an hour or two, it will enlarge because it absorbs the water. Why
is this?
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Substances in the gummy bear that give it solidity are: glucose, starch and
gelatin. All of these substances can absorb (form some interaction with)
water. However, while water can be absorbed, the starch and gelatin are
prevented from dissolving in water. So the water swells the gummy bear rather
than dissolves it.

Think of a very dry sponge such as used for washing dishes. In this form 
it is
a small, hard material. However, it is porous and water can go into those
pores. When water enters the pores, the sponge gets enlarged, and becomes
flexible.

Greg (Roberto Gregorius)
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That sounds like fun.
I bet it gets really soft and flimsy too.
Eventually, in enough water, it will all dissolve.
Gummy bears are made of protein-gelatin, water, and sugar.
It is just extra-thick "Jell-O".
You can make similar yourself by with a Jell-O packet by cutting the water 
and added sugar by a factor of 2-4.
instead of being wet and wiggly it comes out tougher and rubbery and able 
to get dry on the surface.

Or you can make Jell-O shapes and slowwwly dry them out, and watch them 
shrink over the course of a week or a month.
It's exactly the opposite process of your water-swelling.
Better to use sugar-free, keep it in a loosely covered in a transparent 
container, and maybe in the refrigerator so it cannot grow much mold or 
bacteria.
Think twice about eating it if it has been out of the refrigerator a long 
time.

The term "gel" are scientifically recognized as meaning:
"a nano-scale webwork of solid substance filling only a small percentage 
of its apparent volume, the remainder being empty or filled with a fluid".
(I am not quoting anybody, just made that up.)
Gelatin is a gel in which the solid webwork is made of a certain bio-protein.

So, liquids and gasses can penetrate all parts of it, going into it and 
out of it at will, like wind through a jungle-gym, but slower.
And if the webwork is flexible or stretchable, the shape can expand or 
contract in response to the change in fluid content.
Some gels, made of glass or metal oxides rather than protein, are rigid 
instead of flexible.
But Gummy Bears are flexible.

Jim Swenson
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