• Solutions - Homogeneous mixtures of two or more pure substances.

• Solute - Part being dissolved. Usually smaller in quantity.

• Solvent - Thing that dissolves.

• Solvation - Dissolving process.

• Hydration - The dissolving process with water as the solvent.

• Substances depend on these to form solutions.

  • Intermolecular forces

  • Natural tendency to mix.

Natural Tendency to Mix

• Mixing of gases is spontaneous.

• Mixing causes more randomness in the position of molecules increasing the entropy.

Attractions involved when forming a solution

• Solute-solute interactions - Must be overcome to disperse these particles when making a solution.

• Solvent-solvent interactions - Must be overcome to make room for the solute.

• Solvent-solute interactions - Occur as the particles mix.

Energetics of Solution Formation

• ΔH solvent - Energy required to vaporize.

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• Solubility - How much solute can be dissolved in a given amount of solvent at a given temperature.

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• Saturated solutions - Can’t add more solute. More than enough.

• Unsaturated solutions - Can add more. Not enough.

• Supersaturated solutions - Temporary situation where the solution is cooled slowly and for it to react, a crystal from the solute is added.

Factors that affect solubility

• Solute-solvent interactions

• Temperature

  • As it goes up, more solute is dissolved

• Pressure (for gas solutes)

  • As it goes up, more solute can be added.

Pressure Effects

• Solubility of solids and liquids isn’t affected by pressure.

• Gas solubility is affected by pressure

• Henry’s Law - The solubility of a gas is proportional to the partial pressure of the gas above the solution. It’s only true at a constant temperature.

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Temperature Effects on Solubility

• For most solids, as temperature increases, solubility increases.

• For all gases, as temperature increases, solubility decreases.

Solution Concentration Conversion Between Units

• Mass percentage (% m/m)

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• Parts per million (ppm)

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• Parts per billion (ppb)

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• Mole fraction (X)

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• Molarity (M)

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• Molality (m)

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Colligative Properties

• They depend only on the quantity, not on the identity of the solute.

  • Vapor pressure reduction

  • Boiling point elevation

  • Freezing point depression

  • Osmotic pressure

Vapor pressure reduction

• Raoult’s Law

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Boiling point elevation

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• i - Van-Hoff factor, the number of ions you get when dissolving the compound.

• Kb is a constant different for all compounds.

Freezing point depression

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• Kf is a constant different for all compounds.

Osmotic Pressure

• Osmosis - The net movement of solvent molecules from a solution of low to a high concentration of solute across a semipermeable membrane.

  • Semipermeable membrane - Smaller particles pass through it, but it blocks larger particles.

• Osmotic pressure - The applied pressure to stop bigger particles.

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• If two solutions separated by a semipermeable membrane have the same osmotic pressure, no osmosis occurs.

Colloids

• Colloids - Suspension of particles larger than individual ions or molecules, but too small to be settled out by gravity.

  • Ex. → Blood

• They have a hydrophobic end (tail) and a hydrophilic end (head).