SOLUTIONS AND
SOLUBILITY
DEFINITIONS
A solution is a homogeneous mixture
A solute is dissolved in a solvent.
 solute is the substance being dissolved
 solvent is the liquid in which the solute is dissolved
 an aqueous solution has water as solvent
A saturated solution is one where the concentration is at a maximum - no more solute is
able to dissolve.
 A saturated solution represents an equilibrium: the rate of dissolving is equal to the
rate of crystallization. The salt continues to dissolve, but crystallizes at the same rate
so that there “appears” to be nothing happening.
Substances that make up the solution can be:
Solid- salt dissolved in water
Liquid- HCl dissolved in water
Gas- Carbon Dioxide dissolved in water- pop
Not every liquid dissolves every solid ex. NaCl dissolves in
water but not gasoline, parrafin wax dissolves in
gasoline but not water.
Liquids are similar- liquids that dissolve other liquids are
miscible- ethanol dissolves in water.
- liquids that do not dissolve each other are
immiscible- oil and water.
A common phrase that is used to determine which
substances dissolve which is “like dissolves like”.
Meaning polar substances dissolve polar substances
and nonpolar dissolve non polar.
Examples of solutions not in liquid phase:
Air- made of N2, O2 CO2 and others
Metal Alloys- brass- made up of zinc and copper
REACTIONS INVOLVING PRECIPITATES
When two liquids (with dissolved
substances) mix and a solid forms it is
called a precipitate.
REMEMBER- NET IONIC EQUATIONS
When a solution of Pb(NO3)2 is mixed with a solution of KI the
result is a precipitate of PbI and a solution of KNO3.
Pb(NO3)2(aq) + 2KI(aq)  PbI 2(s) + 2KNO3(aq)
Remember- dissociation equations
Net Ionic Equation
% CONCENTRATION
% (w/w) =
% (w/v) =
mass solute
mass solution
x 100
mass solute
volume solution
x 100
volume solute
volume solution
x 100
% (v/v) =
1. How many mL of a 14 M stock solution must be
used to make 250 mL of a 1.75 M solution?
2. You have 200 mL of 6.0 M HF. What concentration
results if this is diluted to a total volume of 1 L?
3. 100 mL of 6.0 M CuSO4 must be diluted to what
final volume so that the resulting solution is 1.5
M?
4. What concentration results from mixing 400 mL of
2.0 M HCl with 600 mL of 3.0 M HCl?
5. What is the concentration of NaCl when 3 L of 0.5
M NaCl are mixed with 2 L of 0.2 M NaCl?
6. What is the concentration of NaCl when 3 L of 0.5
M NaCl are mixed with 2 L of water?
7. Water is added to 4 L of 6 M antifreeze until it is
1.5 M. What is the total volume of the new
solution?
8. There are 3 L of 0.2 M HF. 1.7 L of this is poured
out, what is the concentration of the remaining
HF?
DILUTION PROBLEMS (1-6, 6 TWO
WAYS)
1.
M1 = 14 M, V1 = ?, M2 = 1.75 M, V2 = 250 mL
V1 = M2V2 / M1 = (1.75 M)(0.250 L) / (14 M)
2.
V1 = 0.03125 L = 31.25 mL
M1 = 6 M, V1 = 0.2 L, M2 = ?, V2 = 1 L
M2 = M1V1 / V2 = (6 M)(0.2 L) / (1 L)
3.
M2 = 1.2 M
M1 = 6 M, V1 = 100 mL, M2 = 1.5 M, V2 = ?
V2 = M1V1 / M2 = (6 M)(0.100 L) / (1.5 M)
V2 = 0.4 L or 400 mL
DILUTION PROBLEMS (4 - 6)
4. # mol = (2.0 mol/L)(0.4 L) + (3.0 mol/L)(0.6 L)
= 0.8 mol + 1.8 mol = 2.6 mol
# L = 0.4 L + 0.6 L
# mol/L = 2.6 mol / 1 L = 2.6 mol/L
5. # mol = (0.5 mol/L)(3 L) + (0.2 mol/L)(2 L)
= 1.5 mol + 0.4 mol = 1.9 mol
# mol/L = 1.9 mol / 5 L = 0.38 mol/L
6. # mol = (0.5 mol/L)(3 L) + (0 mol/L)(2 L)
= 1.5 mol + 0 mol = 1.5 mol
# mol/L = 1.5 mol / 5 L = 0.3 mol/L
Or, using M1V1 = M2V2,
M1 = 0.5 M, V1 = 3 L, M2 = ?, V2 = 5 L
DILUTION PROBLEMS (7, 8)
7.
M1 = 6 M, V1 = 4 L, M2 = 1.5 M, V2 = ?
V2 = M1V1 / M2 = (6 M)(4 L) / (1.5 M)
V2 = 16 L
8. The concentration remains 0.2 M, both volume and moles
are removed when the solution is poured out. Remember
M is mol/L. Just like the density of a copper penny does
not change if it is cut in half, the concentration of a
solution does not change if it is cut in half.
% CONCENTRATION: % MASS EXAMPLE
3.5 g of CoCl2 is dissolved in
100mL solution.
Assuming the
density of the solution is 1.0
g/mL, what is concentration of the
solution in % mass?
%m = 3.5 g CoCl2
100g H2O
= 3.5% (m/m)
CONCENTRATION: MOLARITY EXAMPLE
If 0.435 g of KMnO4 is dissolved in enough water to give 250. mL of solution,
what is the molarity of KMnO4?
As is almost always the
case, the first step is to
convert the mass of
material to moles.
0.435 g KMnO4 • 1 mol KMnO4 = 0.00275 mol KMnO4
158.0 g KMnO4
Now that the number of moles of substance is known, this can be
combined with the volume of solution — which must be in liters
— to give the molarity. Because 250. mL is equivalent to 0.250 L .
Molarity KMnO4 = 0.00275 mol KMnO4 = 0.0110
M
0.250 L solution
DILUTION
Suppose you have 0.500
M sucrose stock solution.
How do you prepare 250
mL of 0.348 M sucrose
solution ?
When a solution is diluted, solvent
is added to lower its
concentration.
The amount of solute remains
constant before and after the
dilution:
moles BEFORE = moles AFTER
C 1V 1 = C 2 V 2
Concentration
0.500 M
Sucrose
250 mL of 0.348 M sucrose
A bottle of 0.500 M standard
sucrose stock solution is in the lab.
Give precise instructions to your
assistant on how to use the stock
solution to prepare 250.0 mL of a
0.348 M sucrose solution.
FACTORS AFFECTING SOLUBILITY
1. Nature of Solute / Solvent. - Like dissolves like (IMF)
2. Temperature i) Solids/Liquids- Solubility increases with Temperature
Increase K.E. increases motion and collision between solute / solvent.
ii) gas - Solubility decreases with Temperature
Increase K.E. result in gas escaping to atmosphere.
3. Pressure Factor i) Solids/Liquids - Very little effect
Solids and Liquids are already close together, extra pressure will not
increase solubility.
ii) gas - Solubility increases with Pressure.
Increase pressure squeezes gas solute into solvent.
SOLUBILITIES OF SOLIDS VS
TEMPERATURE
Solubilities of
several ionic solid as
a function of
temperature. MOST
salts have greater
solubility in hot
water.
A few salts have
negative heat of
solution, (exothermic
process) and they
become less soluble
with increasing
temperature.
TEMPERATURE & THE SOLUBILITY OF GASES
THE SOLUBILITY OF GASES DECREASES AT HIGHER TEMPERATURES
SOFT DRINKS
Soft drinks contain “carbonated water” – water with
dissolved carbon dioxide gas.
The drinks are bottled with a CO2 pressure greater than 1
atm.
When the bottle is opened, the pressure of CO 2
decreases and the solubility of CO 2 also decreases
Therefore, bubbles of CO2 escape from solution.
COLLIGATIVE PROPERTIES
Dissolving solute in pure liquid will change all physical properties of liquid, Density,
Vapor Pressure, Boiling Point, Freezing Point, Osmotic Pressure
Colligative Properties are properties of a liquid that change when a solute is added.
The magnitude of the change depends on the number of solute particles in the
solution, NOT on the identity of the solute particles.