Chapter Summary/Important Terms

• Chromatography

• Fractional Distillation

• Factors Affecting Solubility

Factors Affecting Solubility

• Structure: “Like Dissolves Like”

  • Polar dissolves Polar; non-polar dissolves non-polar

• Temperature: Different rules for different types of solutions

• Pressure: Applies to Gas-Liquid Solution

Like Dissolves Like

• Substances that share similar intermolecular interactions tend to be soluble or miscible in one another.

• Miscible - Soluble in all proportions

• Miscible solutions never become saturated.

• Polar Molecules dissolve in polar solvents.

  • eg- Water and Methanol

• Vitamin C

  • Forms H-Bonds at 5 locations

• Glucose

  • Forms H-Bonds at 5

• Polar Solutes dissolve in polar solvents, such as water.

• Non-polar molecules dissolve in Non-polar solvents

  • ex- C6H14 and C8H18

• They form strong london dispersion forces of attraction for one another.

Ionic Compounds in Polar Solvents

• ex - NaCl dissolves in water

Na^+ and Cl^-

• Ions drag a certain number of water molecules around with them in solution.

• Smaller ions have stronger electron fields so they drag more water molecules around with them.

Ion-Dipole and Coulomb’s Law

F = K{(Q1Q2)/d²}

• Some ionic compounds do not dissolve in water.

• The solubility of ionic compounds can be explained through coulomb’s law.

• If cation-anion attractions are stronger than Ion-Dipole attraction, the compound will not be soluble.

• Ionic compounds do not dissolve in non-polar solvents, as non-polar solvents do not carry permanent dipoles.

Ion-Dipole vs Ionic Bonds

• Two forces work against one another through Coulomb’s law.

Chromatography & Solubility

• Chromatography paper is composed of non-polar carbon chains with -OH groups that can form H-bonds.

• The stationary phase is the chromatography paper and the mobile phase is the solvent used.

• As the solvent moves up the piece of paper it carries solute particles with it.

• The distance that the different solute particles travel up the paper depends on their relative attractions for moving the solvent and the stationary paper.

• Solute particles that can form H-bonds at several locations along their structures will not travel very far up the paper, as the molecules in the paper contain many -OH groups.

  • These solute particles will from H-bonds with the paper relatively close to the solutions surface.

• Solute particles that are mostly non-polar will have weak attractions for the paper and relatively strong attractions for the mainly non-polar solute.

  • These particles will be deposited further up the paper.

Fractional Distillation

• The separation of volatile liquids in a liquid-liquid solution on the basis of boiling points.

• If the cycle of boiling and condensing is repeated enough times, complete purification of the more volatile substance can be achieved.

Gas Solubility and Temperature

• The solubility of most gases decreases as temperature increases.

• Gases tend to have weak intermolecular forces.

  • ex - N2 and O2 form weak dipole induced dipole forces and weak dispersion forces with water.

• As the kinetic energy of particles within a solution increases, aqueous particles break free from these weak attractions and re-enter the gas phase.

Beverages and Pollution

• Warm carbonated drinks go flat faster than cold carbonated drinks.

• Thermal pollution:

  • During many industrial processes, water is pumped out of lakes or rivers used to cool equipment, gases, or other liquids.

  • Heat flows into this water

  • The temperature of that body of water increases, drops, and the fish die.

Gas Solubility and Pressure

• Henry’s Law:

  • The solubility of a gas is directly proportional to the partial pressure of that gas above the solution.

• Pressure only affects the solubility of gases.

• When pressure is small, A in the solution is low.

• When pressure is large, A in the solution is high.

• The slope of these lines increase as intermolecular forces increase.

The Bends

• Under high pressure, N2 is much more soluble in blood.

• If you ascend too quickly, the reduction in pressure causes N2 to form N2 is your blood.

  • Can be painful and fatal

• Deep sea divers prevent this by using He in place of N2

  • He exhibits low solubility under high pressures.