2. Formation of solutions
• When a solvent dissolves a solute.
– Solvent: component present in higher
proportion.
– Solute: component present in less proportion.
• Solvent dissolves a solute through the
process of: solvation.
• Each solute has a limit of how much can be
dissolved in a particular solvent. this is
very dependent of temperature (and
pressure in the case of gases). Agitation is
also a factor that influences the rate of
solvation.
• Solubility (physical property) the amount of
solute that can be dissolved in a particular
solvent (at given conditions). It is highly
dependent on temperature (and pressure for
gases).
3. solubility
• For solid + liquid solutions
– Higher Temperature, higher solubility.
• For gas + liquid solutions
– Higher temperature, lower solubility.
– Higher pressure, higher solubility.
4. Solution concentration
• Concentration: measure of the proportion of
solute present in a solution.
– It can be measured in terms of the solute.
– It can be measured in terms of the solution.
• For example:
– A solution made with 70% water, 30% alcohol.
– 1L of solution made with 10 mL aclohol.
5. Measuring concentration
• % volume; % mass (% solute from the
solution)
• In terms of moles:
– Molarity: M=moles of solute/L solution; 0.1M
H2SO4 read: a sulfuric acid 0.1 molar solution.
– molality: m = moles of solute/kg of solvent;
– Normality: N = (moles of solute*n.eq.)/L solution;
• Number of equivalents: related to particles that
separate when in solution.
6. Making dilutions
• Principle: number of moles is kept constant.
• From Molarity= moles solute/L solution…
• Moles solute = Molarity * L solution…
• Therefore, moles = M*V
• Since moles1 = moles2
M1*V1 = M2*V2
• Then, you may calculate volume changes to
dilute/concentrate solutions.
7. Colligative properties
• Properties related to the concentration of a
solution.
• Increase in boiling point.
• Decrease in freezing point.
• Decrease in vapor pressure.
• Etc.
8. Colligative Properties
If the change in boiling/freezing point is:
DTb = Kb*m*i
DTf = Kf*m*i
(i: number of dissolved particles)
Therefore, the boiling/freezing points of a solution:
Tb = Tb
o + DTb
Tf = Tf
o - DTf
9. Concentration of solutions
• How many grams of potassium sulfate must
be added with enough water to make 1.5L of a
1.2M solution?
10. Concentration of solutions
• A solution of water and ethyl alcohol (C2H6O)
is prepared by mixing 2 kg of water and 950 g
of alcohol. What is the freezing and boiling
points of the mixture?
(Kf=1.86 °C/m ; Kb=0.512 °C/m)
