Solubility
Honors Chemistry
Mrs. Jacobus
Components of a Solution
 Solute is the substance being dissolved – powder
 Solvent is the dissolving agent – water
Solute
Dissolve
Solvent
Solubility
The amount of solute that will dissolve in a given amount of solvent.
Soluble vs. insoluble
 May vary with solvent
 “Like dissolves
like”
Polar and Nonpolar
• A polar bond is a covalent bond between two
atoms where the electrons forming the bond
are unequally distributed
• A nonpolar bond is a covalent bond between
two atoms where the electrons forming the
bond are equally distributed
Nonpolar Molecule (CH4)
Polar Molecule (H2O)
“Like dissolves like”
Two substances with similar intermolecular forces (force
between two molecules) are likely to be soluble in each
other.
• non-polar molecules are soluble in non-polar solvents
CCl4 in C6H6
•
polar molecules are soluble in polar solvents
C2H5OH in H2O
•
ionic compounds are more soluble in polar solvents
NaCl in H2O or NH3 (l)
12.2
Factors Affecting Solubility
– Temperature
– Pressure
Solubility is the amount of solute that will dissolve in a given amount
of solvent at a given temperature or pressure.
Factors Affecting the Rate of
Dissolution
– Stirring
– Temperature
– Particle size/Surface
area
A saturated solution contains the maximum amount of a
solute that will dissolve in a given solvent at a specific
temperature.
An unsaturated solution contains less solute than the
solvent has the capacity to dissolve at a specific
temperature.
A supersaturated solution contains more solute than is
present in a saturated solution at a specific temperature.
Sodium acetate crystals rapidly form when a seed crystal is
added to a supersaturated solution of sodium acetate.
12.1
Solubility
Concentration Units
The concentration of a solution is the amount of solute
present in a given quantity of solvent or solution.
Percent by Mass
mass of solute
x 100%
% by mass =
mass of solute + mass of solvent
mass of solute x 100%
=
mass of solution
Mole Fraction (X)
moles of A
XA =
sum of moles of all components
12.3
Concentration Units Continued
Molarity (M)
M =
moles of solute
liters of solution
Molality (m)
m =
moles of solute
mass of solvent (kg)
12.3
What is the molality of a 5.86 M ethanol (C2H5OH)
solution whose density is 0.927 g/mL?
moles of solute
moles of solute
m =
M =
mass of solvent (kg)
liters of solution
Assume 1 L of solution:
5.86 moles ethanol = 270 g ethanol
927 g of solution (1000 mL x 0.927 g/mL)
mass of solvent = mass of solution – mass of solute
= 927 g – 270 g = 657 g = 0.657 kg
moles of solute
m =
mass of solvent (kg)
=
5.86 moles C2H5OH
= 8.92 m
0.657 kg solvent
12.3
Saturated, Unsaturated & Supersaturated
Ex.1)
If 10.0 g of KCl is dissolved in 100.0 g of water at
20.0oC, then would the solution be described as
unsaturated, saturated, or supersaturated?
________________________________________.
unsaturated
Ex.2)
If 10.0 g of KClO3 is stirred into 100.0 g of water at
20.0oC, then would the solution be described as
unsaturated, saturated, or supersaturated?
________________________________________.
saturated with about 1 g of undissolved KClO3
Ex.3)
If 10.0 g of KClO3 is dissolved in 100.0 g of water at
20.0oC, then would the solution be described as
unsaturated, saturated, or supersaturated?
supersaturated
________________________________________.
Saturated, Unsaturated & Supersaturated
Ex.4)
If 100.0 g of KI is stirred into 100.0 g of water at
20.0oC, then would the solution be described
as unsaturated, saturated, or supersaturated?
unsaturated
______________________________________
Ex.5) If 100.0 g of KNO3 is stirred into 100.0 g of water
60.0oC, then would the solution be described
as
unsaturated, saturated, or supersaturated?
unsaturated
______________________________________
at
Ex.6) How many grams of KNO3 will exactly saturate
g of H2O at 20.0oC? ______________
g
≈70
200.0
Temperature and Solubility
Solid solubility and temperature
solubility increases with
increasing temperature
solubility decreases with
increasing temperature
12.4
Temperature and Solubility
O2 gas solubility and temperature
solubility usually
decreases with
increasing temperature
12.4
Watch the following video:
http://www.youtube.com/watch?v=XSGvy2FPfCw
What kind of a solution is it?
Need more help?
• http://www.wwnorton.com/college/chemistry/gil
bert2/tutorials/interface.asp?chapter=chapter_0
4&folder=saturated_solutions
– Norton tutorial on solubility
• http://www.youtube.com/watch?v=zjIVJh4JLNo&
edufilter=d3ViuWqXvxQy1rRgssBz8Q
– Basic solubility
• http://www.youtube.com/watch?v=4VltXjR64SU
&edufilter=d3ViuWqXvxQy1rRgssBz8Q
– Molarity vs. Molality