Chapter 13
Ions in Aqueous Solutions and
Colligative Properties
Ratios and Molarity
• M1V1=M2V2
• M is Molarity and V is Volume
– Doesn’t matter what volume is in. They just have
to be the same.
– How many mL of a 6M solution would you need to
dilute it to 250 mL of a 3 M solution?
– What is the concentration of 550 L, if you dilute
400 L of a 3.75M solution?
Compounds in Aqueous Solutions
• Ionic- metal and nonmetal
• Covalent (Molecular)- nonmetal and nonmetal
• Dissociation: the separation of ions that occur
when an ionic compound dissolves.
• Reactions
– s is solid
– aq is aqueous
– L is liquid
Dissociation (Ionic Equations)
• When writing reactions with ions, the
equation is balanced for charge as well as for
atoms.
• We are going to take equations and break
down the compounds into their elements.
• Do examples
Precipitation Reactions
• Although no ionic compound is completely
insoluble, compounds of very low solubility
can be considered insoluble for most practical
purposes.
• We are going to learn some general solubility
rules. This doesn’t cover every thing, but
most.
Solubility Rules
• Sodium potassium and ammonium compounds are soluble
in water.
• Nitrates, acetates, and chlorates are soluble
• Most chlorides are soluble.
– Except silver, mercury (I), and lead
– Lead (II) chloride is soluble on in hot water
• Most sulfates are soluble
– Except those of barium, strontium, lead, calcium, and mercury
• Most carbonates, phosphates, and silicates are insoluble
– Except sodium, potassium, and ammonium
• Most sulfides are insoluble
– Except calcium, strontium, sodium, potassium, and ammonium
Net Ionic Equations
• Net ionic equations include only those
compounds and ions that undergo a chemical
change in a reaction in an aqueous solution.
• To write a net ionic equation,
1.
2.
3.
4.
Write and balance the regular equation.
Determine if soluble or insoluble.
Only change the soluble into ions
Check for spectator ions
Examples
• Identify the precipitate that forms when
aqueous solutions of zine nitrate and
ammonium sulfide are combined. Write the
equation for the possible doubledisplacement reaction. Then write the overall
ionic equation, and net ionic equation for the
reaction.
Examples
• Let’s do the practice problems on page 440
Hydronium Ion
When an acid mixes with water it can form what
we call a hydronium ion (H3O+)
Colligative Properties
• Properties that depend on the concentration
of solute particles but not on their identity
– The boiling and freezing point differ from those of
the pure solvent.
– To calculate the new melting point and freezing
point we will be using the formulas
• ∆tf=Kfm or ∆tb=Kbm
• We will be using the table on your solubility sheet
Examples
• What is the freezing-point depression of water
in a solution of 17.1 g of sucrose, C12H22O11 in
200 grams of water? What is the actual
freezing point of the solution?
• A water solution contain an unknown quantity
of a nonelectrolyte solute is found to have a
freezing point of -.23oC. What is the molal
concentration of the solution?
Examples
• What is the boiling-point elevation of a
solution made from 20.1 g of a nonelectrolyte
solute and 400.0 g of water? The molar mass
of the solute is 62.0 grams.
Homework
• Practice problems on page 450 and 451 (1-4
on both)
Electrolytes and Colligative Properties
• Colligative properties depend on the total
concentration of solute particles regardless of
the identity. The changes in colligative
properties caused by electrolytes will be
proportional to the total molality of all
dissolved particles, not to formula units.
• The salts applied to icy roads are electrolytes.
They lower the freezing point of water and
melt the ice.
Examples
• What is the expected change in the freezing
point of water in a solution of 62.5 g of barium
nitrate, Ba(NO3)2, in 1.00kg of water?
Homework
• Do the practice problems on page 455