Factors Determining Solubility (4.1.4)

Question 1

• Polar solutes dissolve in polar solvents.

Answer 1

• Polar solutes dissolve in polar solvents.

Question 2

• Nonpolar solutes dissolve in nonpolar solvents.

Answer 2

• Nonpolar solutes dissolve in nonpolar solvents.

Question 3

Elements on the left of the periodic table are
electron rich (electropositive). Elements on the
right of the periodic table are electron needing
(electronegative). Elements from opposite sides of
the periodic table tend to form ionic bonds.
Hydrogen and oxygen have different affinities for
electrons. The bond between hydrogen and
oxygen is still a covalent bond, but the large
difference in the electronegativity of hydrogen and
oxygen results in a large dipole moment—the
hydrogen atoms are partially positive (δ
+), and the oxygen atom is partially negative (δ–). A covalent bond in which the electrons are distributed unevenly between the two bonding atoms is called a polar covalent bond.
Polar solutes (such as ions) dissolve in polar
solvents (such as water). This is because the
charges on the solvent (for example, the partial
charges on the atoms in water) shield the charges
of the solute (for example, the positive charge on
sodium ion or the negative charge on chloride ion).
This shielding prevents the ions from “seeing” one
another to form an ionic bond.
Solubility of nonpolar solutes is governed by the
disorder of the system, rather than by attractions
between charged species. This disorder is called
entropy. The entropy of a system tends to
increase.
When a polar solute (salt) is added to a nonpolar
solvent (hexane), the solvent is forced to become
more ordered to accommodate the polar solute.
Therefore, polar solutes tend not to dissolve in
nonpolar solvents. Similarly, when a nonpolar
solute (oil) is added to a polar solvent (water), the
entropy decreases. Therefore, nonpolar solutes
tend not to dissolve in polar solvents. However,
when a nonpolar solute (oil) is added to a nonpolar
solvent (hexane), the entropy increases. Therefore,
nonpolar solutes dissolve in nonpolar solvents.

Answer 3

Elements on the left of the periodic table are
electron rich (electropositive). Elements on the
right of the periodic table are electron needing
(electronegative). Elements from opposite sides of
the periodic table tend to form ionic bonds.
Hydrogen and oxygen have different affinities for
electrons. The bond between hydrogen and
oxygen is still a covalent bond, but the large
difference in the electronegativity of hydrogen and
oxygen results in a large dipole moment—the
hydrogen atoms are partially positive (δ+), and the
oxygen atom is partially negative (δ–). A covalent
bond in which the electrons are distributed unevenly
between the two bonding atoms is called a polar
covalent bond.
Polar solutes (such as ions) dissolve in polar
solvents (such as water). This is because the
charges on the solvent (for example, the partial
charges on the atoms in water) shield the charges
of the solute (for example, the positive charge on
sodium ion or the negative charge on chloride ion).
This shielding prevents the ions from “seeing” one
another to form an ionic bond.
Solubility of nonpolar solutes is governed by the
disorder of the system, rather than by attractions
between charged species. This disorder is called
entropy. The entropy of a system tends to
increase.
When a polar solute (salt) is added to a nonpolar
solvent (hexane), the solvent is forced to become
more ordered to accommodate the polar solute.
Therefore, polar solutes tend not to dissolve in
nonpolar solvents. Similarly, when a nonpolar
solute (oil) is added to a polar solvent (water), the
entropy decreases. Therefore, nonpolar solutes
tend not to dissolve in polar solvents. However,
when a nonpolar solute (oil) is added to a nonpolar
solvent (hexane), the entropy increases. Therefore,
nonpolar solutes dissolve in nonpolar solvents.