8.2 Factors that Affect Rate of
Dissolving and Solubility
Learning Goals …
… identify factors that affect the RATE of dissolving
… identify factors that affect the AMOUNT of
dissolving (solubility)
… use a solubility curve to answer problems about
solubility
Collision Theory: chemical reactions can only occur if reactants
collide with proper orientation and enough kinetic energy to
break reactant bonds and form product bonds
Three Factors Affect the Rate of Dissolving:
Temperature:
 Temperature  rate
• the solvent particles have higher kinetic energy and
therefore collide with undissolved solute particles more
frequently.
Agitation:
 Agitation  rate
• more solvent particles come into contact with undissolved
solute particles.
Particle size:
 Surface Area ( Particle size)  rate
• the amount of surface area of the solute is increased
therefore more exposure to the solvent.
Factors Affecting Solubility
**Like dissolves like**
Polar solutes dissolve in polar solvents;
Non-polar solutes dissolve in non-polar solvents
Water can dissolve Ionic Compounds and Polar
Molecular Compounds but not Non-polar Molecular
Compounds
Temperature
 T  solubility
• there is more energy to break the bonds between the
solvent ions or molecules.
Dissolving an Ionic Compound
When the force of attraction between water and the ionic
compound (intermolecular force) is stronger than the force of
attraction holding the solid ionic compound together
(intramolecular force), then the ionic compounds will split
apart and dissolve, forming a solution. This attraction is
called an ion-dipole interaction.
• Ionic Compounds will have greater solubility if the ions are
easier to pull apart:
Ion Size:
 Size  solubility
• Larger ions are farther apart and have a weaker attraction
 are easier to pull apart (eg KCl > NaCl)
Ion Charge:  charge  solubility
• Larger charges have a stronger attraction  are harder to
pull apart (eg NaCl > MgCl2)
Dissolving a Molecular Compound
When the force of attraction between water and the polar
compound is stronger than the force of attraction between
the solid polar compound molecules, then the polar
compounds will separate and dissolve, forming a solution.
This attraction is called a dipole-dipole attraction.
Molecule size
 size  solubility
• Small molecules are more soluble than large ones
Polarity
• since water is polar it can only dissolve polar molecules,
not non-polar molecules
Rank the following in order of most soluble to least soluble:
LiOH, CH4, NaOH, Ca(OH)2
Solubility curves, show what mass of solute will dissolve in
100g of water over a range of temperatures.
10g
At 30°C approximately _____
of KClO3 will dissolve in 100g
of water.
If the temperature is
increased to 80°C,
40g of the
approximately ______
substance will dissolve in
100g of water.
Solubility curves, show what mass of solute will dissolve in
100g of water over a range of temperatures.
100g
At 80°C approximately _____
of KCl will dissolve in 200g of
water.
If the temperature of a KNO3
solution is decreased from
70°C to 50°C, approximately
50g of the substance will
______
recrystallize.
If 30 g of KCl is dissolved in
100 g of water at 70°C, is the
solution unsaturated,
unsaturated,
supersaturated?
saturated, or supersaturated?
saturated
CAN I …
… identify factors that affect the RATE of dissolving
… identify factors that affect the AMOUNT of
dissolving (solubility)
… use a solubility curve to answer problems about
solubility
HOMEWORK
p370 #3-10
WS “Solubility Curves”