SOLUTIONS AND SOLUBILITY

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SOLUTIONS AND SOLUBILITY
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Within a solution, the substance that is the
dissolving medium (what something else is
dissolved in), is called the solvent. The solute
is the substance dissolved in the solvent. If
you make salt-water, the salt is the solute, and
the water is the solvent.
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1. What is a Solution?
Any substancesolid, liquid, or gasthat is
evenly dispersed or distributed throughout
another substancesolid, liquid, or gasis a
solution.
Solutions can be called homogeneous mixtures
because they are not pure substances, yet the
substances that comprise them are evenly
dispersed throughout the mixture.
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Some liquids are soluble in each other, like
alcohol and water.
These 2 substances are so soluble in each other,
that as you add more water to alcohol, the water
concentration becomes greater than the alcohol
concentration, and becomes the solvent. So,
solvent and solute should not be thought of as
absolutes.
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TYPES OF SOLUTIONS
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The Process of Solvation
The process of dissolving a solute in a solvent
is called solvation. This occurs when the
molecules of the solute are hydrated, or
completely surrounded by solvent
molecules. Miscibility The ability of liquids
to dissolve in each other. Example Water
Alcohol Like dissolves like Polar dissolves
polar Non-polar dissolves non-polar. If
liquids cant dissolve or mix, they are said to
be immiscible. Example Oil Vinegar
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SOLUBILITY
Solubility is the amount of substance needed to
make a saturated solution at a given temperature.
A saturated solution is one that cannot dissolve
any more solute at a given temperature. When you
have a saturated solution, adding more solute
merely gives you a clump of solid in the bottom
of the container. The solvent molecules cannot
hold any more. We would call a solution that IS
able to dissolve more solute an unsaturated
solution. A supersaturated solution is one that
has been forced to dissolve more solute by
increasing the temperature or pressure.
Supersaturated solutions are very unstable.
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Factors Affecting Solubility
PRESSURE
Increase pressure Increase solubility
An example of this is a soda bottle. The CO2 in
the system is forced into the solution, and is
held under pressure. When you open the bottle,
the pressure is reduced, and the CO2 rushes out
of the bottle. If you leave the lid off, the
soda goes flat, because all of the CO2 escapes.
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TEMPERATURE
Have you noticed that your hand soap, as well as
your laundry soap, tends to do a better job in
hot or warm water? The soaps do a better job
because they are able to hold more stuff at
higher temperatures. As a general rule for most
substances, solubility increases with an increase
in the temperature of the solution.
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Solubility Curve

• Normally, as temperature increases, solubility
  increases.
• This can be represented on a solubility curve.
• This lets us know exactly how much of a solute
  can be dissolved in a solvent at a certain
  temperature.
• For instance, lets look at the curve for
  potassium nitrate

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Size

• Smaller particles dissolve faster and easier.

Stirring or Shaking

• Moving the particles around increases the rate of
  dissolution.

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• WORKSHEET FOR SOLUTIONS
• Of the following, which are homogeneous mixtures
  and which are heterogeneous mixtures black
  coffee, household bleach, tea, maple syrup, cream
  of mushroom soup?
• 2.On the basis of the principle like dissolves
  like, determine which is more soluble in water,
  ammonia or carbon dioxide? Explain your choice.
  Use a reference to evaluate your choice. The
  Merck Index is a useful resource.
• 3.Why is using water to clean a paintbrush
  covered with an oil-based enamel paint not an
  effective method of clean-up?
• 4.Using your knowledge, derive a rule of thumb
  about the relationship between the solubility and
  the temperature of a solution. List any
  exceptions.
• 5.Predict what will happen when a solute is added
  to a saturated solution at a constant
  temperature.
• 6.How can a supersaturated solution be prepared?