Solutions

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Solutions

• Section 15.1

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Solutions
Solutions are homogeneous mixtures containing two
or more substances called the solute and the
solvent. The solvent is the largest part of the
solution and the solute is the smallest part of
the solution
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Solutions
Even though most solutions are liquid, solutions
do exist as solids, liquids and gases.
Gases Air Oxygen Nitrogen
Liquids
Solid Alloys
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Solubility
Some substances readily combine to form
solutions, others do not. A substance that
dissolves in a solvent is said to be soluble.
For example, sugar is soluble in water. A
substance that will not dissolve in a solvent is
said to be insoluble, like oil and water.
Oil and Water Insoluble
Sugar and Water Soluble
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Solubility
If two liquids are soluble in each other they are
said to be miscible. If two liquids will not
dissolve, they are immiscible.
Oil and Water Immiscible
Water and alcohol Miscible
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Solvation
Solvation is the process of the solute particles
breaking apart the solute crystal into particles
the size of ions. If water is the solvent, this
is accomplished by the polarity of the water
molecule. One of the characteristics of a
solution is that the particles of solute do not
settle to the bottom of the container. This
occurs because the particles (atoms and ions) are
so small that they are unaffected by gravity.
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The Tyndall Effect and Colloids
Another characteristic of solutions is that they
do not exhibit the Tyndall Effect. Because the
solute is broken down into ion sized particles,
light waves are able to pass through a solution
without being dispersed. In a colloid, the
breakdown of solute stops at the molecular size,
and the larger particles disperse light and give
colloids a characteristic cloudy appearance.
Solution
Colloid
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Aqueous Solutions of Ionic Compounds
When an ionic substance such as salt is solvated
by water, the sodium and chloride ions are
suspended in the water as charged particles, and
the solution is said to be an electrolyte because
it will conduct electricity. One of the more
commonly recognized electrolytes is Gatorade
because it restores sodium and potassium to the
human body and allows our nervous system to work
efficiently.
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Aqueous Solutions of Molecular Compounds
Molecular compounds such as sugar, that are
covalently bonded, do not break apart into ions.
Instead, the positive end of the hydrogen bond of
the water molecules combine with the negative end
of the hydroxide (OH) sites and pull apart
individual molecules from the molecular crystal.
This creates a neutral particle, and as a result,
molecular compounds do not form electrolytes like
ionic compounds do.
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Factors that Affect the Rate of Solvation

• Solvation can be increased by increasing
  the number of times atoms or molecules touch each
  other, and this is done by
• Agitating (mixing, stirring, shaking) the mixture
• Increasing the surface area of the mixture
• Increasing the temperature of the mixture

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Solubility
Solubility refers to the maximum amount of solute
that will dissolve in a given amount of solvent
at a specified temperature and pressure. As a
substance is being solvated, eventually a point
will be reached where the particles of solute
will begin to collide and reform the crystal. At
this point, the solute is said to be in
equilibrium, or saturated.
This solution is saturated because Solvation
Crystal Formation
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Solubility Curves
Each substance has its own unique solubility, and
chemical solubility is depicted on a solubility
curve. A saturated solution contains the maximum
amount of dissolved solute for a given amount of
solvent at a given temperature and pressure.
?Supersaturated
?Saturated
?Unsaturated
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Solubility Curve Practice
1. Which salt is least soluble in water
at 20C? 2. How many grams of potassium
Chloride can be dissolved in 200 g of
water at 80C? 3. At 40C, how much potassium
nitrate can be dissolved in 300 g of
water?
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Solubility Curve Practice
4. Which salt show s the least change in
solubility from 0 to 100C? 5. At 30C, 90 g
of sodium nitrate is dissolved in 100 g of
water. Is the solution saturated,
unsaturated, or supersaturated? 6. A saturated
solution of potassium chlorate is formed from
100 g of water. If the solution is cooled from
80C to 50C, how many grams of precipitate are
formed?
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Solubility Curve Practice
7. What compound shows a decrease in
solubility form 0C to 100C? 8. Which salt is
most soluble at 10C? 9. Which salt is least
soluble at 50C? 10. Which salt is least soluble
at 90C?
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Supersaturated Solutions

• A supersaturated solution is one that is
  holding more solute than a saturated solution at
  the same temperature and pressure. The diet coke
  and Mentos explosion is a good example of this.
  The CO2 that is present in a carbonated drink is
  much greater than the normal saturation level for
  CO2. When nucleated sites (Mentos) are placed
  into the carbonated drink, suddenly the CO2
  jumps out of solution and the famous Mentos
  explosion occurs.

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Temperature and Solubility
As temperature is increased, the solubility of a
solid solute will generally increase. As the
temperature is increased, the solubility of a gas
will decrease.
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Pressure and Solubility
The solubility of any gas increases as the
external pressure is increased this phenomena is
described by Henrys Law. All carbonated
beverages are based on this law. Once you pop
the top on a Coke, the external pressure has
been reduced, and the solubility of the CO2 goes
down. This is why a Coke goes flat in a very
short time. Henrys Law is described by the
following equation S1 S2 P1 P2
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Henrys Law Problems

• If 0.55 g of a gas dissolves in 1.0 L of water at
  2 atm of pressure, how much will dissolve at 4.5
  atm of pressure?
• 2. A gas has a solubility of 0.66 g/L at 10 atm
  of pressure. What is the pressure on a 1.0 L
  sample that contains 1.5 g of gas?

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Henrys Law Practice Problems
3. If .68 g of a gas at 5 atm of pressure
dissolves in 1.0 L of water at 25C, how
much will dissolve in 1.0 L of water at 8 atm of
pressure and the same temperature? 4.
A gas has a solubility of 1.46 g/L at 8 atm of
pressure. What is the pressure of a 1.0 L
sample that contains 2.7 g/L?
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Solubility Curve