Properties of Solutions

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Properties of Solutions
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A Solution is

• A homogeneous mixture
• The substances in the mixture are in the same
  physical state
  (solid, liquid, or gas)

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Gas solution

• Air is a homogeneous solution of different gases
• Nitrogen, oxygen, water vapor, carbon
  dioxide.etc.

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Solid Solution

• Metals are often mixed together to form a solid
  solution called an ALLOY
• Brass is a solid solution of zinc and copper

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Liquid Solution

• Most of the solutions in Chemistry are in the
  liquid phase
• Most common solution is a solid substance
  dissolved in a liquid

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Liquid Solution solvent solute

• Solute is the solid (present in small amounts)
• Solvent is the liquid (present in large amounts)
• When the 2 are mixed, the final result is a
  solution

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Liquid Solution solvent solute
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Solvents

• The most common solvent is water. It is often
  called the Universal Solvent. Many (but not
  all!) substances will dissolve in water
• Can you think of a substance that does NOT
  dissolve in water?

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Aqueous Solutions

• A solution made with water as the solvent is
  called an aqueous solution (aq)
• NaCl (s) Na (aq) Cl- (aq)

A salt water solution
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Solvents

• There are solvents other than water. These are
  often used to dissolve substances that do not
  dissolve in water.
• Can you think of a type of solvent besides water?

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What do liquid solutions look like?

• homogeneous mixtures
• Clear, not cloudy
• May have color
• The solute does not settle to the bottom
• Pass through filters

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Are these solutions?
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Are these solutions?
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Solubility

• Substances that dissolve easily are called
  SOLUBLE
• Salt is soluble in water

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Solubility

• Substances that do not dissolve easily are called
  insoluble
• Nickel is insoluble in water

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Factors that influence solubility

• Why are some substances soluble in water, but not
  in other liquids?
• Why are some substances not soluble in water?
• What can be done to make a substance dissolve
  more easily?
• It helps to understand what controls solubility.

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Factors that influence solubility

• 1 TEMPERATURE
• As temperature increases, most solids become more
  soluble in water.
• Ex. Sugar in ice tea vs. hot tea

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Factors that influence solubility

• 1 TEMPERATURE
• As temperature increases, most gases become less
  soluble in water.
• Ex. The carbon dioxide (fizz) in cold soda vs.
  hot soda

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Factors that influence solubility

• 2 Pressure
• As pressure increases, most gases become more
  soluble in water.
• Ex. The carbon dioxide (fizz) in soda in a
  pressurized can vs. soda that has been left open
  (goes flat at low pressure)

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Factors that influence solubility

• 2 Pressure
• PRESSURE HAS NO EFFECT ON LIQUID OR SOLID
  SOLUTES!!!

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Factors that influence solubility

• 3 The Nature of the solute and solvent
• where like refers to the polarity of the
  molecule

Like dissolves Like
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Factors that influence solubility

• 3 The Nature of the solute and solvent
• POLAR solvents dissolve POLAR solutes
• (Polar includes ionic compounds)

Like dissolves Like
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Factors that influence solubility

• 3 The Nature of the solute and solvent
• POLAR solvents dissolve POLAR
  solutes
• So ionic NaCl will dissolve in polar water

Like dissolves Like
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What is going on at the molecular level when a
polar substance dissolves?
Na
Cl-
The polar water molecule pulls apart the
ionic compound into anions and cations If you
evaporate away the water, the Na and Cl will join
together again to make NaCl (s)
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Na
Cl-
For this to happen, the attraction between the
positive end of the water molecule and the
negative ion must be STRONGER than the attraction
between the positive and negative ion.
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Factors that influence solubility

• 3 The Nature of the solute and solvent
• NON POLAR solvents dissolve
• NON POLAR solutes
• Non polar solvents and solutes simply mix together

Like dissolves Like
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Factors that influence solubility

• 3 The Nature of the solute and solvent
• fats and oil are non polar
• Oil (non polar) will not dissolve
• in water (polar)

Like dissolves Like
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Soaps

• Soaps are long molecules that have a polar end
  and a non polar end
• Grease (non polar) does not dissolve in water
  alone (polar), but if soap is added, the grease
  will dissolve in the non polar end of the soap.
  The polar end of the soap allows it to dissolve
  in the water, washing away the grease