Colligative properties
Solutions Part 4
Electrolytes: a quick review
• Electrolytes form ions
in solution.
• Ions allow water to
conduct electric
current
• Three types of
electrolytes: strong ,
weak, and nonelectrolytes.
Strong Electrolytes
• Strong electrolytes ionize
completely in water.
• More ions in the water, more
conductivity.
• Strong electrolytes include:
– Strong acids HCl H+ + Cl– Strong bases NaOH Na+ + OH– Soluble salts CaCl2 Ca2+ + 2Cl-
Molarity:review
• Moles per liter
• 1.0 M = 1 mole
solute per 1 liter
solution.
• Question
• What is the molarity
of 1.56 g of gaseous
HCl in a 26.8 mL
solution?
Mole Fraction
• mole fraction: the
number of moles of a
component of a
solution divided by
the total number of
moles of all
components.
Example:
• 58.5 grams of NaCl are in a one liter
solution.
• What is the Molarity of the NaCl?
• 1M
• 58.5 grams of NaCl are in 1800 grams of
water.
• What is the mole fraction of NaCl?
• 1/101
Molality
• Definition: a unit of concentration, defined
to be equal to the number of moles of
solute divided by the number of kilograms
of solvent .
This is not to be confused with Molarity
Why so you add salt to an icy
sidewalk?
•
•
•
•
It melts the ice.
How?
Colligative properties.
Why so some types of salt seem to work
better than melting the ice than others.
• Why?
• Colligative properties.
Colligative properties
• are properties of solutions
that depend on the
number of molecules in a
given volume of solvent
and not on the properties
(e.g. size or mass) of the
molecules.[1] Colligative
properties include:
lowering of vapor
pressure; elevation of
boiling point; depression
of freezing point and
osmotic pressure.
Colligative properties
• How many ions are
formed from the
dissociation of 1mole
of NaCl?
• From CaCl2?
• From NH4Cl
• From H3PO4?
Question
• What is the
concentration of each
type of ion in the
following solutions?
• 0.50M Co(NO3)2
• 1 M Fe(ClO4)3
Answer
• Co 2+
• NO3 -
0.5 M
1.0 M
• Fe 3+
• ClO4 -
1M
3M
• Why isn’t it 3M Cland 12 M O2- ??
Vapor Pressure Reduction
• The particle act to
attract the water
molecules making it
more difficult for them
to free themselves to
become vapor.
Freezing point depression
• The individual
particles interfere with
the water’s ability to
form a crystal
depressing the
freezing point.