SOLUTIONS AND SOLUBILITY
WORKSHEET
Read the following sections to answer the following questions:
8.2 – Solutions and Their Characteristics
8.3 – The Dissolving Process
8.5 – Solubility and Saturation
Types of Solutions (8.2, 8.3, 8.5)
1. Define: solution, solute, solvent, concentrated solution,
dilute solution, aqueous solution, miscible, immiscible,
hydration, dissociation, solubility, saturated, unsaturated,
supersaturated solution.
2. Do: page 381 #1, 3, 9
The Dissolving Process (8.3)
3. Describe the process of dissolving.
4. Do ionic compounds dissolve in polar or nonpolar solvents?
5. What are hydrated ions and electrolytes?
6. Do: page 389 #7, 8, 13ab
SOLUBILITY AND INTERMOLECULAR FORCES
Recall: Intermolecular forces are the forces between
molecules that hold molecules to each other (also called
Van der Waals forces).
Dipole-Dipole Attractions
 A dipole results from the asymmetrical charge
distribution in a polar molecule.
 The bent shape and polar bonds of a water molecule
give it a permanent dipole.
 These are only ~1% as strong as ionic or covalent
bonds.
 A special dipole-dipole attraction occurs between
water molecules, called hydrogen bonding, which is
much stronger than ordinary dipole-dipole attraction.
Ion-Dipole Attraction
 Refers to the attractive forces between an ion and a
polar molecule.
 Ionic compounds generally tend to dissolve in a polar
solvent.
For Example:
Sodium chloride (NaCl) will “dissolve” in water
forming Na+ cations and Cl- anions. Each will be
surrounded by water molecules (each ion becomes
hydrated).
 Compounds that have strong ionic bonds tend to be
less soluble in water. Why?
Predicting Solubility
 Comparing the electronegativity between two
elements reveals if the compound is ionic, polar, or
nonpolar.
 Polar and ionic compounds dissolve in water.
For Example:
HgS
Since ΔEN is small, the compound is
insoluble in water.
Covalent Compounds
 Most do not have positive and negative charges to
attract water molecules, do not have polar bonds, and
therefore are not soluble.
 Some exceptions exist: sugars, methanol, and ethanol
are very soluble since their molecules contain polar
bonds (these form hydrogen bonds with water
molecules).
o These molecules become hydrated but
remain neutral. They do not form ions (nonelectrolytes).
Generally:
“Ionic or polar covalent solutes dissolve in polar solvents”
AND
“Nonpolar solutes dissolve in nonpolar solvents”
This is commonly expressed as “LIKE DISSOLVES LIKE”
 Some compounds possess polar and nonpolar bonds,
which means that they can dissolve in both types of
solvents.
Factors that Affect Rate of Dissolving
1. Temperature:
 For most solid solutes, the rate of dissolving is
greater at higher temperatures. At higher
temperatures, the solvent molecules have greater
kinetic energy (the energy of motion). Thus, they
collide with undissolved solid molecules more
frequently.
2. Agitation:
 Agitating a mixture by stirring or shaking the
container increases the rate of dissolving. Agitation
brings fresh solvent into contact with undissolved
solute.
3. Size of Particles:
 Decreasing the size of particles increases the rate
of dissolving.
Factors that Affect Solubility
1. Molecule Size:
 Smaller molecules are generally more soluble than
larger ones.
Explain why methanol is much more soluble than
pentanol.
2. Temperature:
For a solid solute dissolving in a liquid solvent:
o As temperature increases, more energy is
provided to break more bonds, and thus
solubility increases.
For a liquid solute dissolving in a liquid solvent:
o The solubility of most liquids is not greatly
affected.
For a gas solute dissolving in a liquid solvent:
o As temperature increases, solubility decreases.
Plotting Solubility Curves (see graph).
3. Pressure:
 Little to no effect on solid and liquid solutions, but a
BIG effect on solubility of a gas in a liquid solvent.
 The solubility of a gas is directly proportional to the
pressure of the gas above the liquid.