Excellent question! Liquid water is an amazing
fluid— it is possibly the most relevant molecule
that keeps us and most living things on Earth
One important property of water is that it can
hold other molecules or ions (charged particles).
Salt, for instance, is made of two ions called
sodium (Na+) and chloride (Cl-). When salt is put
in water, the water itself will actually seem to
absorb the ions because it is attracted to these
charges. Pure water can hold large amount of salt
without changing its volume very much— in fact,
for every 1 pound of water, you could hold over
1/3 pound of salt in it!
The key concept here is that the density of water
changes when you add salt. Density is measured by
taking the weight of the liquid divided by its
volume. Adding salt will gradually increase the
water’s density. You can prove this by dropping
something like a carrot slice into pure
water—observe that it should sink to the bottom
because carrot is denser than regular water. But
by adding salt to the water, eventually you will
see the carrot float up to the top! This is
because the water density is slowly increasing and
eventually becomes denser than the carrot.
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