Transcript Solutions
SOLUTIONS
Chapter 15
What are solutions?
Homogeneous mixtures containing two or more
substances called the solute and the solvent
Solute- is the substance that dissolves
Solvent- is the dissolving medium
May exist as a solid, liquid or gas (usually are liquids)
Soluble- A substance that dissolves in a solvent
Insoluble- A substance that does not dissolve in a
solvent (ex. Sand is insoluble in water)
Immiscible- Two liquids that are insoluble in each
other (ex. Oil and water)
Miscible- Two liquids that are soluble in each other
(ex. Vinegar (water + acetic acid) )
Examples of Solutions
Solvation in Aqueous Solutions
Why are some substances soluble in one another
whereas others are not?
Solvation-
the process of surrounding solute
particles with solvent particles to form a solution
Solvation
“Likes
in water is called hydration
dissolve likes”
This phrase means that polar solvents
dissolve polar solutes and nonpolar
solvents dissolve nonpolar solutes.
Oil- Non Polar
Water- Polar
Factors that affect the rate of solvation
Solvation occurs only when and where the solute
and solvent particles come in contact with each
other
Commons ways to increase the collisions
Agitating
the mixture (stirring and shaking)
Increasing the surface area of the solute (breaking the
solute into smaller pieces)
Increasing the temperature of the solvent (increases the
kinetic energy)
Solubility
Solubility refers to the maximum amount of solute that
will dissolve in a given amount of solvent at a specified
temperature and pressure
Saturated solution- contains the maximum amount of
dissolved solute for a given amount of solvent at a specific
temperature and pressure
Unsaturated solution- contains less dissolved solute for a
given temperature and pressure than a saturated solution
Supersaturated Solution- contains more dissolved solute
than a saturated solution at the same temperature (and if
you messed with the solution by shaking it or throwing in one
more crystal, the whole thing would crystallize rapidly!)
Supersaturated Sodium Acetate Solution
Factors that Affect Solubility
Temperature
Many
substances are more
soluble at high temperatures
than at low temperatures
Pressure
Solubility
of a gas in a
solvent increases as its
external pressure (the
pressure above the solution)
increases
Henry’s Law
At a given temperature, the solubility (S) of a gas in
a liquid is directly proportional to the pressure (P)
of the gas above the liquid.
Formula:
S1 S 2
P1 P2
Practice Problem
S1 S 2
P1 P2
A gas has a solubility of 0.66 g/L at 10.0 atm of
pressure. What is the pressure on a 1.0-L sample
that contains 1.5 g of gas?
Solution Concentration
The concentration of a
solution is a measure of how
much is dissolved in a
specific amount of solvent or
solution
Qualitative Vocabulary
Dilute- contains a small amount of
solute
Concentrated- contains a large
amount of solute
concentrated
dilute
Expressing Concentration
Concentration description
Percent by mass
Ratio
mass of solute
x 100
mass of solution
Percent by volume
volume of solute
x 100
volume of solution
Molarity
molesof solute
liter of solution
Molality
molesof solute
kilogramof solvent
Mole Fraction
moles of solute
moles of solute moles of solvent
Calculating Percent my Mass
What is the percent my mass of NaHCO3 in a
solution containing 20 g NaHCO3 dissolved in
600mL H2O?
Calculating Percent by Volume
What is the percent by volume of ethanol in a
solution that contains 35 mL of ethanol dissolved in
115 mL of water?
Calculating Molarity
What is the molarity of an aqueous solution
containing 40.0g of glucose (C6H12O6) in 1.5 L of
solution?
Preparing Molar Solutions
How many grams of NaOH are in 250mL of a 3.0M NaOH
solution?
Diluting Solutions
M1xV1=M2xV2
• M1 -- the initial concentration of the solution.
• V1 -- the initial volume of the original solution that is going
to be diluted with water.
• M2 -- the final concentration of the solution after it’s
diluted with water.
• V2 -- the total volume of the final solution after it has
been diluted with water.
Practice Problem
What volume of a 3.00M KI stock solution would you use to
make 0.300 L of a 1.25M KI solution?
If you dilute 20.0 mL of a 3.5M solution to make 100.0 mL of
solution, what is the molarity of the dilute solution?
Calculating Molality
What is the molality of a solution containing 30.0g
of napthalene dissolved in 500.0g of toluene?
Calculating Mole Fraction
An aqueous solution of NaCl has a mole fraction of
0.21. What is the mass of NaCl dissolved in
100.0mL of solution?
Colligative Properties of Solutions
Physical properties of solution that are affected the
number of particles but not the identity of dissolved
solute particles
Colligative Properties include:
Vapor
Pressure Lowering
Boiling Point Elevation
Freezing Point Depression
Osmotic Pressure
Vapor Pressure Lowering
The greater the number of solute particles in a
solvent, the lower the resulting vapor pressure
Boiling Point Elevation
The temperature difference between a solution’s
boiling point and a pure solvent’s boiling point
Formula: ∆Tb= Kbm
Kb is
the molal boiling point elevation constant
m is the molality
The
value of the boiling point elevation is directly
proportional to the solution’s solute molality- the
greater the number of solute particles in the solution,
the greater the boiling point elevation
Freezing Point Depression
The temperature difference between a solution’s
freezing point and a pure solvent’s freezing point
Formula: ∆Tf= Kfm
Kf is
the molal boiling point elevation constant
m is the molality
Increasing Temperature
Practice Problem
What are the boiling point and freezing point of a
0.40m solution of sucrose in ethanol?
Osmosis and Osmotic Pressure
Osmosis is the diffusion of solvent particles across
a semipermeable membrane from an area of
higher solvent concentration to an area of lower
solvent concentration
Osmotic Pressure- the amount of additional
pressure caused by the water molecules that moved
into solution
Depends upon the number of solute particles in a given
volume of solution