4B Chapter 13 Notes

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4B Chapter 13 Notes
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Dissociation

• Stephanie Hutchinson
• Tre Jennings

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Dissociation

• Dissociation The separation of ions that occurs
  when an ionic compound dissolves.
• Chemical equations in dissociation require
  balanced charge as well as atoms.
• For now, 100 dissociation can always be assumed.

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Example

• The dissociation of NaCl can be represented as
  follows
• NaCl(s)?Na(aq)Cl-(aq)
• The dissociation of Al2(SO4)3 can b e represented
  as follows
• Al2(SO4)3(s)?2Al3(aq)3SO42-(aq)

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Net Ionic Equation
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What is a net ionic equation?

• A net ionic equation includes only those
  compounds and ions that undergo a chemical change
  in a reaction in an aqueous solution.

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Writing a net equation

• First convert the chemical equation into an
  overall ionic equation.
• All soluble ionic compounds are shown as
  dissociated ions in solution.
• The precipitates are shown as solids.
• Ions that do not take part in a chemical reaction
  and are found in solution both before and after
  the reaction are spectator ions.

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• General Equation
• Cd(NO3)2(aq) (NH4)2S(aq) ?
• CdS(s) 2NH4NO3(aq)
• Complete Ionic Equation
• Cd2(aq) 2NO3-(aq) 2NH4(aq) S2-(aq) ?
  CdS(s) 2NO3-(aq) 2NH4(aq)
• Net Ionic Equation
• Cd2(aq) S2-(aq) ? CdS(s)

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Electrolytes

• By Pariis Yi, Chase Young, Joey Wofford, Parker
  Meek, Jonathan Binkley

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Electrolytes A general overview

• Electrolyte substance that dissolves in water to
  give a solution that conducts an electric current
• A mole of an electrolyte dissolves to make two
  moles in the solution
• Non-electrolyte the substance that does not
  yield ions and does not conduct an electric
  current in solution

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Colligative Properties

• Electrolyte is an ionic compound
• Non-ionic compounds cannot form electrolytes
• Depends on number of parts

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Strong Electrolytes

• Strong Electrolyte any compound whose dilute
  aqueous solutions conduct electricity well
• There is a presence of all or almost all of the
  dissolved compound in the form of ions
• There is a higher concentration of ions

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Example

• NaCl(s) Na(aq) Cl-(aq)

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Weak Electrolytes

• Weak Electrolytes any compound whose dilute
  aqueous solutions conduct electricity poorly
• There is a presence of a smaller amount of the
  dissolved compound in the form of ions
• There is a lower concentration of ions

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Example

• H2CO3(aq) H(aq) HCO3-(aq)

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Freezing Point Depression

• Abby Brazinski Natasha Zelenka

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• The freezing point of a 1m solution of any
  nonelectrolyte solute in water is 1.86C lower
  than the freezing point of water.
  
• The molal freezing point constant for water is
  -1.86C/m.
• The molal freezing point constant is the
  freezing-point depression of the solvent in a
  1-molal solution of a nonvolatile nonelectrolyte
  solution.
• Each solvent has its own freezing point constant.

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Freezing Point Depression

• Freezing-point depression, ?tf , is the
  difference between the freezing points of the
  pure solvent and a solution of a nonelectrolyte
  in that solvent, and it is directly proportional
  to the molal concentration of the solution.

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Equation

• Equation ?tf Kfm
• Kf is expressed as C/m
• m is mol solute/kg solvent (molality)
• ?tf is expressed as the freezing-point depression
  and is expressed in C
• See page 449 in the textbook for an example.

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Osmic Pressure

• Allison Johnson
• David Holland, Jr.

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Definitions

• Osmic Pressure is the external pressure that must
  be applied to stop osmosis
• Osmosis movement of a solvent through a semi
  permeable membrane from the side of higher
  concentration to lower concentration
• Semi permeable membrane allows some particles
  to pass through while preventing others.

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Other facts

• Is dependent on concentration of particles, not
  the type of particles in the solutions
• Greater the concentration of a solution, the
  greater the osmic pressure

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Example

• On one side of the semi permeable membrane is a
  solution (salt water) and on the other would be
  the pure solvent (water). Because of the presence
  of the NaCl molecules in the solution, the
  solvent is blocked and fewer water molecules are
  able to reach the membrane and pass through than
  on the side with pure water

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Example

• The pure water passes through the membrane faster
  and raises the volume of the solution until the
  pressure exerted by the height of the solution is
  enough to force the water molecules in the
  solution back through the membrane at the same
  rate the water passes through on the other side.

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Vapor Pressure Lowering

• Kaitlynn Motley
• Artaza Khan
• Ishaan Sandhu

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Vapor Pressure

• -- The pressure caused by molecules in the gas
  phase that are in equilibrium with the liquid
  phase

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Colligative Properties

• -- Properties that depend on the concentration of
  solute particles but not on their identity
• Unit molality (m)

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Nonvolatile Substances

• -- Substance that has little tendency to become a
  gas under existing conditions
• Raises boiling point
• Lowers freezing point
• When solute in solution, has lower vapor pressure
  than vapor pressure of pure solvent
• Vapor pressure of solution less than pure water

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Properties

• Nonelectrolyte solutions w/ same molality have
  same particle concentration
• Equally dilute molal solutions of any type of
  nonelectrolyte solvent in any solution lower
  vapor pressure equally
• Lowering depends on concentration of
  nonelectrolyte solute
• Independent of solute identity
• Colligative property

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example

• Vapor pressure of water over pure water greater
  than vapor pressure of water over an aqueous
  solution containing a nonvolatile solute

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Boiling-Point Elevation

• Taylor Walsh
• Justin Corr
• Brendan Korando

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The cool slide

• A change in vapor pressure of a liquid will cause
  a change in the boiling point.
• The boiling point of a solution is higher then
  boiling point of a solvent.

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Molal Boiling-Point Constant

• Kb
• The boiling point elevation of a solvent in a
  1-Molal solution of a nonvolatile, nonelectrolyte
  solute.
• The Molal Boiling point constant for water is .51
  degrees Celsius/m

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Boiling Point Elevation

• The difference between the boiling points of the
  pure solvent and a nonelectrolyte solution of
  that solvent, and it is directly proportional to
  the molal concentration of the solution.
• ?tb Kbm
• Kb degrees Celsius/m
• ?tb The boiling Point Elevation

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EXAMPLE