Bell Work: Colligative Properties

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Bell Work Colligative Properties

1. Vapor pressure goes ( up / down) with more solute
   added.
2. Vapor pressure is closely related to ( freezing /
   boiling ) point.
3. Colligative properties depend on the ( type /
   number ) of particles.
4. Why does salt melt ice?

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• Remember The more solute particles that
  are in the solution, the more the colligative
  properties are affected!

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Lets Summarize

• Ionic Compounds will dissociate and produce
  electrolytes that are capable of conducting an
  electric current
• The following solutes are placed into water.
  What happens to these solutes as they begin to
  dissolve?

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They dissociate into
2 moles of ions

• NaCl ?
• MgCl2 ?
• Na3PO4 ?

1 Na1 1 Cl-1
1 Mg2 2 Cl-1
3 moles of ions
3 Na1 1 PO4-3
4 moles of ions
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• Q Which substance above produces more solute
  particles in solution?

A Na3PO4 therefore, it will have the most
influence on colligative properties
Remember A colligative property depends on
the number of solute particles in solution, not
the identity of the particles
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• Covalent solutes dissolve, but they do NOT
  dissociate into ions. Why?
• They do NOT have regions of opposite charge to
  attract to the nonpolar solvent!

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• Instead, covalent substances dissolve as whole
  molecules.
• The whole molecules form nonelectrolytes and they
  DO NOT conduct an electric current!

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nonelectrolyte
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• The solutes below are placed into
• water. What happens to these
• solutes as they begin to dissolve?
• C6H12O6 ?
• C12H22O11 ?
• They dissociate one molecule at a
• time!

1 mole of particles
1 C6H12O6
1 C12H22O11
1 mole of particles
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• Q Which covalent substance above
• would have the most influence on
• colligative properties?

A Neither! They would have the same effect
b/c each covalent compound produces only ONE
mole of solute particle and colligative
properties depend on the number of particles!
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Lets Summarize

• Covalent Compounds will dissociate into only one
  mole of particles and produce nonelectrolytes
  that are NOT able to conduct an electric current!

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• Now its your turn!
• Why do ionic compounds more strongly affect
  colligative properties than covalent compounds?
• Ionic compounds always dissociate into two or
  more particles while covalent compounds always
  dissociate into only one! Since colligative
  properties depend on the NUMBER of particles, and
  ionic compounds produce more particles, they
  affect colligative properties more!

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How does the addition of a solute affect each of
the 3 colligative properties?

• Vapor pressure decreases with addition of solute
  to solvent!
• There are solute particles interfering with the
  solvent particles at the surface of the solution.
  
• Less of the solvent can evaporate and push
  upwards b/c the solute is at the surface, too.
• Since less solvent is evaporating, vapor pressure
  drops b/c there is not gas pushing upwards.

vapor pressure
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Vapor Pressure of a Solution A Colligative
Property Which flask has a lower vapor pressure?
Explain. Flask A Flask B Pure
Solvent Solution (no solute present)
Solute Solvent
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How does the addition of a solute affect each of
the 3 colligative properties?

• Boiling point elevates (increases) with addition
  of a solute to a solvent.
• For a substance to boil, atmospheric pressure
  pushing down must equal vapor pressure pushing
  up.
• Solute particles interfere with the solvent
  particles at the surface.

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• It will take more energy to get the solvent
  particles to push their way to the surface to
  evaporate.
• This means you have to heat the solution up to a
  higher temperature to give the solvent particles
  more energy to increase vapor pressure.

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How does the addition of a solute affect each of
the 3 colligative properties?

• Freezing point depresses (decreases) with
  addition of solute to solvent.
• Solute particles are mixed in with the solvent
  particles interfering with the ability of solvent
  particles to get close together.

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• The solute is in the way.
• This means temperature has to drop A LOT for the
  solvent to push the solute out of the way in
  order to get close together and solidify.

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Ionic Compounds
Covalent Compounds
nonpolar (no oppositely charged poles)
polar (have and regions)
since no ions, they dissociate one particle at a
time
dissociate into two or more particles at a time
ions are called electrolytes
no ions so they are called non-electrolytes
conduct electricity
non-conductors of electricity
strongly affect colligative properties
more weakly affects colligative properties