Ions in Aqueous Solutions and Colligative Properties

1
Chapter 14

• Ions in Aqueous Solutions and Colligative
  Properties

2
Chapter 14.1

• Dissociation is the separation of ions that
  occurs when an ionic compound dissolves.
• NaCl Na Cl-

H2O
Na
Na
3
General Solubility Guidelines pg 427

1. Most sodium, potassium, and ammonia compounds are
   soluble in water.
2. Most nitrates, acetates, and chlorates are
   soluble.
3. Most chlorides are soluble, except those of
   silver, mercury (I), and lead. Lead (II) chloride
   is soluble in hot water.
4. Most sulfates are soluble, except those of
   barium, strontium, and lead.
5. Most carbonates, phosphates, and silicates are
   insoluble, except those of sodium , potassium,
   and ammonium.
6. Most sulfides are insoluble, except those of
   calcium, strontium, sodium, potassium, and
   ammonium.

4

• Will a precipitate form when ammonium sulfate and
  cadmium nitrate combine??
• Write the dissociation for each compound
• (NH4)2S 2 NH4 S2-
• Cd(NO3)2 Cd2 2NO3-
• Check the Solubility Guidelines to make sure they
  will dissociated.
• Write the double replacement reaction if they are
  both soluble.
• (NH4)2S Cd(NO3)2 (NH4)2(NO3) CdS
• Check both products solubility on the chartCdS
  is insoluble so it is the precipitate.

H2O
H2O
5

• Net ionic equation includes only those compounds
  and ions that undergo a chemical change in a
  reaction in an aqueous solution. (Not spectator
  ions)
• Spectator ions are ions that didnt take part in
  a chemical reactions. They are found on both
  sides of the reaction.
• Cd2 2NO3- 2NH4 S2- CdS 2NO3-
  2NH4
• Spectator Ions NO3- and NH4
• Cd2 2NO3- 2NH4 S2- CdS 2NO3-
  2NH4
• Net Ionic equation
• Cd2 S2- CdS

6

• Ionization is when ions are from solute molecules
  by the action of the solvent. In general mean
  the term is the creation of ions where there were
  none.
• Ionization is different from dissociation.
• Ionization happens with covalent (molecular)
  compounds and dissociation happens with ionic
  compounds.
• Hydronium ion H or H3O

7

• Strong electrolytes are any compound of which all
  or almost all of the dissolved compound exists as
  ions in an aqueous solution. (most acids and all
  ionic compounds)
• Weak electrolytes is a compound of which a
  relatively small amount of dissolved compoud
  exist as ions in an aqueous. (covalent compounds)

8
Chapter 14.2

• Colligative properties are those that depend on
  the concentration of particles in a solution, not
  upon the identity of those properties.
• Boiling Point Elevation
• Freezing Point Depression
• Osmotic Pressure

9
Freezing Point Depression

• tf kfm
• Each mole of solute particles lowers the freezing
  point of 1 kilogram of water by 1.86 C.
• Kf constant table 14-2
• mmolal moles/kg
• tf change in temp
• That is why we salt the roads!!!!

10
Boiling Point Elevation

• tb kbm
• Each mole of nonvolatile solute particles raises
  the boiling point of 1 kilogram of water by 0.51
  C.
• Kb constant
• m molal
• tf change in temp

11

• Osmotic pressure is the external pressure that
  must be applied to stop osmosis.
• Osmosis is the movement of solvent through a
  semipermeable membrane from the side of lower
  solute concentration to the side of higher solute
  concentration.
• Semipermeable allow the movement of some
  particles while blocking the movement of others.

12

• Dissociation. April 23, 2007.
  http//www.biologycorner.com/resources/dissociatio
  n.gif
• Test Tubes. April 23, 2007. http//www.myerscons
  ultingservices.net/beaker_rainbow_close.jpg