Solutions

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Module 15
Solutions
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What is a solution? A solution is a mixture that
has the same composition, color, density, and
even taste throughout. A solution is composed of
two parts solute and solvent. The solute is the
dissolved substance. The solvent is the
dissolving medium. Salt water, for example, is a
solution. Salt is the solute and water is the
solvent. Water is the dissolving medium for many
substances and is therefore called the universal
solvent.
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In what phases do solutions occur? Although many
think of solutions as only liquids, there are
gaseous and solid solutions as well. An alloy is
a mixture (solution) of metals. Two or more
metals are melted together, mixed, then poured
into molds.
Read page 708
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Examples of solutions in different states of
matter Solid in liquid ? salt water Liquid in
liquid ? antifreeze Gas in liquid ? carbonated
drink Solid in solid ? alloy Gas in gas ?
air Liquid in gas ? humidity (water in the
air) Solid in gas ? solid air freshener
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What factors affect how fast something
dissolves? (rate of dissolving) Crystal size
the smaller the crystal size, the faster the
solute dissolves. Decreasing the size of the
particles, increases the surface
area. Temperature the higher the temperature,
the faster the solute dissolves (except for a gas
dissolved in a liquid) Catalyst a catalyst is a
substance which increases the speed of a reaction
without changing. Enzymes in the human body begin
to break down food quickly.
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Gas in solutions gases dissolved in a
liquid Pressure The greater the pressure, the
more gas can dissolve into a liquid. Temperature
The greater the temperature, the less gas will
dissolve into a liquid. Soft drinks should be
kept in refrigeration to keep them from going
flat.
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Dissolving Without Water Some liquids do not
dissolve in water. Oil and water do not mix. Oil
is nonpolar (do not have separate positive and
negative areas). Water is polar (has separate
positive and negative areas.
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Polar and nonpolar substances do not mix.
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What is soap? Soap is a special molecule which is
polar at one end and nonpolar at the other end.
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How much can dissolve? Solubility is the maximum
amount of mass of a solute which will dissolve in
given amount of solvent at a specific temperature.
The table to the right is an example of some
solubililties of different substances. Notice
that sugar is much more soluble than salt.
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Types of solutions Saturated solution as much
solute as possible is dissolved at a given
temperature. Solubility Curves Lines (curves)
on a graph which show points of saturated
solution. On the next slide you will see
solubility curves for different substances.
Different substances have varying solubility as
the temperature changes. Some are greatly
affected by temperature and some are not.
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Each point on the curve is a point of saturation
saturated solution.
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Unsaturated solutions a solution in which more
solute may dissolve. One granule of sugar placed
in one cup of water is an unsaturated solution.
As more sugar is added, it continues to be
unsaturated until no more sugar can dissolve. At
this point, it is saturated. Supersaturated
solutions more solute than normal dissolved in
a solvent for a given temperature. How are
supersaturated solutions made? When water is
heated to a high temperature, then a solute is
saturated in the water when the water is then
cooled, it will contain more solute than normal.
Supersaturated solutions are unstable and
release energy.
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What are the effects of solute particles added to
water? Freezing Point Depressions the freezing
point of water is lowered as solute particles are
added. Salt is added to roads in the winter to
lower the freezing point of water. (also ice
cream maker) Boiling Point Elevation the
boiling point of water is increased as solute
particles are added. Car radiators antifreeze
is added to water to both increase the boiling
point and decrease the freezing point to keep the
engine from overheating or freezing.
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This concludes Module 15