# Solubility

GCSE AQA

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Solute: A substance that dissolves in a solvent to form a solution (usually a solid)
Solvent: The liquid in which a solute dissolves in to form a solution (Usually a liquid)
Solution: Is a solute dissolved in a solvent to form a solution ­ (an aqueous solution
is where the solvent is water)
Solubility is how much (number of grams) of a solute dissolves in a 100 grams of a solvent
a particular temperature. The solubility of a solid usually increases with temperature.
Saturated Solution: A solution that contains the maximum amount of solute that it will
dissolve at that temperature
E.g. Copper sulphate dissolves in water when stirred which can be told by the
change is colour of the solution as it goes blue. Why do we stir??? To evenly
distribute the particles, when particles are evenly distributed the substance has
dissolved ­ Other things that speed up even distribution of particles are temperature
as increasing the temperature provides more energy for the particles to move
around.
Solubility of Solids
Most ionic compounds are soluble in water, most covalent compounds are insoluble
in water. Solids are more soluble in warmer solvents.
A saturated solution has dissolved as much solute as possible at a particular
temperature. If you continue to add solute to the solution and heat it up then the solute
will continue to dissolve in the solvent until the solution becomes saturated once again. If
you decrease the temperature/ cool down a saturated solution the solute will separate
from the solution usually in the form of crystals ­ you can find the mass of these
crystals using a solubility curve.

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Here the solution is saturated at 100 degrees so no further solute can be taken into the
solution at that particular temperature. The type of question you could get would be something
like: What is mass of copper sulphate will crystallise when a solution containing 100g of water
is cooled from 100 degrees to 60 degrees?
To work out this question you go to 100 degrees and read across the scale to find the value
of 'solubility/100g water' which is 165g (yellow line).…read more

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Solubility in gases
Many gases are soluble in water e.g. Carbon dioxide, oxygen and chlorine. The solubility of a
gas increases as the temperature decreases ­ this is the opposite to solubility in solids. The
solubility of a gas increases as the pressure increases ­ the higher the pressure the more
gas dissolves. (So basically more gas will dissolve in a solvent if the temperature is low and
pressure is high.)
Examples of gases dissolved in solvents.…read more