What is "dissolve?"
That word has lots of meanings, but when we talk about liquids, and use
the word "dissolve," it means "to become liquid."
There are some substances that are solid or "hard" that will
turn to liquid and mix in with liquid when they are put into a container
of liquid.
We have here
some sugar cubes, marbles, salt, nails, soil, coins, and powdered soap.
We have 7 small jars that have water in them. We will put sugar cubes
into one jar, marbles into another jar, and so on, until each solid thing
we have is in a jar of water. Each jar needs to be stirred or shaken (sometimes
shaking a jar of liquid is messy, so we'll put lids on the ones we shake),
then let them stand a few minutes to see if the stuff in the water will
dissolve or not. It would be a good idea to keep track of the time it
takes each solid to dissolve.
It is fun
to watch sugar cubes dissolve, isn't it? They sort of change shape, and
get smaller and smaller, then they are gone. Where did they go? They dissolved.
They turned into liquid, and if the liquid were stirred, the sugar would
be mixed with the water.
Did the nails
dissolve? It's a good thing they didn't, because if nails could dissolve
in water, our houses would fall apart when it rained!
Let's make
a list of things that dissolve in cool water, and another list of things
that do not.
We can try
it again with warm or hot water, and by keeping track of the time, we
can list things according to how fast they dissolved. That way, it is
easy to tell which
temperature of water is best for dissolving things.
Different
liquids can be tried, and different kinds of solid things. If we try to
dissolve solids in alcohol or gasoline, we must do it with adult supervision,
outside, and be very careful that the alcohol or gasoline do not get heated.
Alcohol and gasoline burn, and can be VERY DANGEROUS.
05 December 2011
26 November 2011
Solution
Virtually all varieties of homogeneous mixtures can be classified as a solution—that is, a homogeneous mixture in which one or more substances is dissolved in another substance. If two or more substances were combined in exactly equal proportions, this would technically not be a solution; hence the distinction between solutions and the larger class of homogeneous mixtures.
A solution is made up of two parts: the
solute, the substance or substances that are dissolved; and the solvent,
the substance that dissolves the solute. The solvent typically
determines the physical state of the solution: in other words, if the
solvent is a liquid, the solution will most likely be a liquid. Likewise
if the solvent is a solid such as a metal, melted at high temperatures
to form a metallic solution called an alloy, then when the solution is cooled to its normal temperature, it will be solid again.
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