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Unit 11— Solutions Factors affecting solvation
Unit 11—
Solutions Factors affecting solvation
The Solvation Process
Attractive forces exist among the particles of
all substances
London Dispersion
Dipole-dipole
Hydrogen bonding
If the attractive forces between the solute
and the solvent are greater than the
attractive forces holding the solute particles
together, the solute dissolves in the solvent
The Solvation Process
Solvation is the process of surrounding solute particles with solvent particles to form a solution.
Solvation in water is called hydration.
For ionic compounds that dissolve in water, the attraction between dipoles of a water molecule and the ions of a crystal are greater than the attraction among ions of a crystal.
How do you know if a
substance will dissolve?
The general rule is “like dissolves like.”
Polar will dissolve polar (or ionic)
Nonpolar will dissolve nonpolar
Is oil polar or nonpolar?
Since it does not dissolve in water, and water
is polar, oil is nonpolar
Sucrose (sugar) molecules have several O–H
bonds, which become sites for hydrogen
bonding with water molecules. That’s why
sugar dissolves in water.
During solvation, the solute must separate
into particles and move apart, which
requires energy
The overall energy change that occurs
during solution formation is called the
heat of solution.
When energy is released, it is an exothermic
process and feels warm or hot.
When energy is absorbed, it is an
endothermic process and feels cool or
cold.
Factors that affect rate of
dissolving of solid in liquid
1. Agitation
Stirring or shaking moves dissolved particles away
from the contact surfaces more quickly and
allows new collisions to occur.
This is why you stir your tea after you put sugar in
it.
2. Surface area
Breaking the solute into small pieces increases
surface area and allows more collisions to occur.
This is why you use granulated sugar instead of
sugar cubes
Factors that affect rate of
dissolving of solid in liquid
3. Temperature
As temperature increases, rate of solvation
increases.
Particles are moving faster.
This is why sugar dissolves faster in hot tea
than in iced tea.
Solubility
Solubility depends on the nature of the
solute and solvent.
Solubility is affected by increasing the
temperature of the solvent because the
kinetic energy of the particles increases.
Solubility of solids in liquids
Generally increases with an increase in
temperature (some exceptions)
Not affected by pressure
Solubility of gases in liquids Increases with an increase in pressure
(Henry’s Law)
This is how carbonated beverages are
made and why they go flat if left open
As the diver goes deeper in
the water, pressure
increases, allowing more
gases (N2) to dissolve in his
blood
If the diver goes to the surface
too quickly, the gases will un-
dissolve in his blood vessels
instead of his lungs
This results in the bends
(decompression sickness,
caisson’s disease. . .)
Solubility of
gases in liquids
How is the solubility of gases affected by temperature?
Solubility of gases decreases with an increase in temperature
This is why soda at room temperature goes flat faster than soda in the refrigerator
Thermal pollution What do fish breathe?
O2 dissolved in water
If these cooling towers dump hot water into the lake, what happens to the temperature of the water?
Increases
What happens to the O2 dissolved in the water?
Decreases
What happens to the fish?
They could suffocate
There are now regulations on how much the temperature of water can be affected by dumping hot water used for cooling
Summary of factors that affect
solubility
Solubility of
solids in liquids
Solubility of
gases in liquids
Increase
temperature
Increase
pressure
Summary of factors that affect
solubility
Solubility of
solids in liquids
Solubility of
gases in liquids
Increase
temperature Generally increases
Increase
pressure
Summary of factors that affect
solubility
Solubility of
solids in liquids
Solubility of
gases in liquids
Increase
temperature Generally increases Decreases
Increase
pressure
Summary of factors that affect
solubility
Solubility of
solids in liquids
Solubility of
gases in liquids
Increase
temperature Generally increases Decreases
Increase
pressure No effect
Summary of factors that affect
solubility
Solubility of
solids in liquids
Solubility of
gases in liquids
Increase
temperature Generally increases Decreases
Increase
pressure No effect Increase
p. 511 127-129, 86-88, 93, 94
