As you may know, there are some substances that
can be dissolved in water (think about salt or
sugar: you can put a spoonful of salt into a glass
of water and stir, and eventually the salt
disappears! It hasn't actually disappeared, of
course; it's just been dissolved into the water).
This dissolving happens when the individual
atoms or molecules of the solid substance (called
the "solute") mix with the individual molecules of
water (called the "solvent"). The result is what
is called a "solution".
However, there is a limit to how much solute
you can dissolve in a given amount of solvent (if
you try to add too much salt to the glass of
water, eventually it will stop dissolving). When
the amount of solute becomes too high, it wants to
start leaving the solution and forming a separate
solid again. It does this by a process called
"precipitation": the individual atoms or
molecules of the solute will start to attach to
one another and form small crystals; as more
and more atoms attach to these crystals, they
become bigger and bigger.
To go back to the salt example, imagine that
you dissolve as much salt as you can into the
glass of water. Now, if you leave the glass out,
the water will start to evaporate, but the amount
of salt in the water will remain the same. That
means that some of the salt needs to leave the
solution, since the smaller amount of water can't
hold it all. So the salt will start to form
crystals of salt; eventually, once all of the
water has evaporated, all that will be left in the
glass are crystals of salt.
Click Here to return to the search form.