Solubility and
Concentration
Chemistry
Mrs. Coyle
Part I Solubility:
 The ability of a solute to dissolve in a solvent.
 Expressed as g solute/100g H2O
or
g solute/100mL H2O
Soluble
• Soluble: a solute that has appreciable solubility.
Miscible
 Substances that dissolve in each other.
Solubility Curves
Precipitate: solute that comes out of
solution.
•
Types of Solutions
 Saturated contains the maximum amount of
solute that can be dissolved at the given
conditions of T and P.
 Unsaturated contains less than the saturated
amount of solute.
 Supersaturated contains more than the
saturated amount of solute by dissolving at
higher temp and then cooling.
A supersaturated solution crystallizes
after a seed crystal is introduced.
http://www.chem.ufl.edu/~itl/2045/change/C12F11.GIF
Rates of Solution
 Does every candy you eat take the same time
to dissolve?
Factors affecting the rate of dissolving:
 Surface Area
 Stirring
 Temperature (average kinetic energy)
Factors Affecting Solubility
 Temperature (affects solid, liquid and
gaseous solutes)
 Pressure (affects gaseous solutes)
Effect of temperature on solubility of
gases.
Example:
Compare the amount of oxygen dissolved in
the waters of the arctic ocean
to the amount of oxygen dissolved in warm
tropical waters.
Effect of temperature on solubility of
solids.
 Example:
Can you dissolve more sugar in warm water
or in cold water?
Solubility
Curves
Effect of Pressure on solubility of
solids.
 Negligible.
Effect of Pressure on solubility of
gases.
 Henry’s Law: the amount of gas dissolved in
a solution is directly proportional to the
pressure of the gas above the solution.
 The higher the pressure the higher the
solubility of the gas.
Effect of Pressure on solubility of
gases.
http://www.chem.ufl.edu/~itl/2045/lectures/lec_i.html
Example
An unopened bottle of soda has a pressure of
5atm above the liquid, so the concentration of
CO2 in the soda is high.
Compare that to a pressure of 1 atm above
the liquid when the bottle has been opened.
Part II Concentration:
 A measure of the amount of solute dissolved in
the solution.




Molarity (M)
Molality (m)
Mole Fraction (x)
Percent by Mass (%)
Part II
 Concentration
Molarity
• A unit of concentration of a solution
expressed in moles solute per liter of
solution. (Note: 1L = 1 dm3)
Molarity (M) =
Moles of Solute
Liters of Solution
Why Molarity ?
http://www.chem.ucla.edu/~gchemlab/volumetric_soln_conc.jpg
Steps involved in the preparation of a
standard aqueous solution
Process of making 500 mL of a
1.00 M acetic acid solution
Ex. 1 Molarity
 What is the molarity of a solution of 8g NaOH
in 100mL of solution?
 Answer: 2M NaOH
Ex. 2 Molarity
 How many grams of NaOH are contained in
2L of a 3M NaOH solution?
 Answer: 240g NaOH
Making Dilutions
 Moles Solute=M1V1=M2V2
 M molarity
 V volume
Ex. 3 Dilutions
 How many milliliters of 2.00M MgSO4
solution must be diluted with water to prepare
100.00 mL of 0.400M MgSO4?
 Answer: 20.0mL
Percent by Mass
% by mass= Mass of solute x 100 %
Mass of solution
Percent by Volume
% by volume= Volume of solute x 100 %
Volume of solution
Part III Molality and Mole Fraction
Molality
 Moles of Solute per kilogram of Solvent
Molality (m) = moles solute
kg solvent
Mole Fraction
xsolute = Moles of solute
Moles of solution
xsolvent = Moles of solvent
Moles of solution
xsolute + xsolvent= 1