Properties of Solutions
13.1 The Solution Process

Solution – homogeneous mixture



Solute – present in smaller quantity
Solvent – present in larger quantity
Intermolecular forces are rearranged when a
solute and solvent are mixed.
Will a solution form?



Solute-solvent interaction must be stronger or
comparable to the separation of solute and
solvent particles.
Intermolecular forces play a key role.
Entropy (disorder) is also a factor.


Disorder is favorable. (2nd law of thermodynamics)
Solution formation increases entropy.
Entropy in Solution Formation
Ionic compound
very ordered
As the ionic compound dissolves, it
becomes more disordered.
An ionic crystal dissolving in water
Saturated Solutions and Solubility

Saturated solution – solution is in equilibrium
with undissolved solute.
dissolution
Solute + solvent
⇌
solution
crystallization


Unsaturated – less solute than saturated
Supersaturated – more solute than saturated
A Saturated Solution
A dynamic equilibrium – ions
continually exchange between
the solid and solution form.
Factors affecting the rate of dissolving

Higher temperatures


Agitation by mixing


Most solids dissovle better at higher temperatures
Brings fresh solvent into contact with undissolved
solid
Decreasing the size of the particles

Increases the surface area
Factors Affecting Solubility
1. Like dissolves like, i.e. same polarity.



Polar solutes are soluble in polar solvents.
Nonpolar solutes are soluble in nonpolar solvents.
If two liquids: miscible or immiscible
Examples:
✔ Soluble: water + alcohol, NaCl + water, hexane +
✘
pentane
Insoluble: water + hexane, NaCl + benzene, oil +
water
Factors Affecting Solubility
2. Molecular size.

Larger molecules are more difficult to surround
with solvent molecules in order to solvate the
substance.
13.3 Factors Affecting Solubility
3. Temperature Effects


For solids: Solubility ↑ as temperature ↑ (usually).
For gases: Solubility ↓ as temperature ↑ (always).
Ionic
compounds
Gases
(In liquids)
13.3 Factors Affecting Solubility
4. Pressure


Liquids and solids exhibit
practically no change of solubility
with changes in pressure.
Only effects gases dissolved in
liquid solvents.
 If the pressure is increased,
the gas molecules are "forced"
into the solution since this will
best relieve the pressure that
has been applied.