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Water - Solubility - Ions

What is Solubility?

Many solids and gases dissolve in water.
Solubility is a measure of
the amount of a substance that can be dissolved.


Most ionic solids dissolve in water, most covalent solids do not.
The amount of solid dissolved in water is given in units of
grams of solid per 100 grams of water.

You can not keep dissolving more and more solid
in the same amount of water. Eventually,
no more solid will dissolve and the solution is called saturated.
If you increase the temperature of the solution (heat it up)
and keep adding solid, then more solid will dissolve
until the solution becomes saturated again.
If you decrease the temperature of the saturated solution
(cool it down) then some of the solid will
come out of the solution (see crystallisation).

You can plot a graph of
the maximum amount of dissolved solid against temperature.
This is called the solubility curve for that particular solid.


Many gases dissolve in water.
Examples are carbon dioxide, chlorine and oxygen.

The solubility of a gas increases as the temperature decreases.
This is the opposite of the solubility of solids.

Also, the solubility of a gas increases as the pressure increases.
A solubility curve for a gas can be shown as
a graph of the maximum amount of dissolved gas
against temperature or pressure.

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