Solutions

Heterogeneous mixture

A non-uniform mix with visibly separate parts.

Homogeneous mixture (Solution)

A uniform mixture with evenly distributed components.

What is a solvent?

• The substance that dissolves another.

• Largest in concentrations.

What is a solute?

• The substance being dissolved.

• Dispersed at lower concentrations.

Particle concentration calculation …

What is dissolution?

The process of a solute dissolving into a solvent to form a solution.

Breaking solute-solute and solvent-solvent attractions …

• H > 0

• Always endothermic

Breaking solute-solvent attractions …

• H < 0

• Always exothermic

What is Hess’ Law for total enthalpy?

Total enthalpy change equals the sum of its individual step reactions.

Endothermic conditions

• Old attractions are stronger than new attractions

• Reactant bonds are stronger than the product bonds

• Solute-solute and solvent-solvent attractions are strongest

Exothermic dissolution

• New attractions are stronger than old attractions

• Product bonds are stronger than the reactant bonds

• Solute-solvent attractions are strongest

What is a weak electrolyte?

• Ionizes only partially in solution.

• Conducts electricity poorly.

What is a strong electrolyte?

• Dissociates completely into ions.

• Conducts electricity effectively

What is a nonelectrolyte?

• A substance that does not form ions when dissolved.

• Dissolves entirely as intact molecules.

• Does not conduct electricity.

Polar-polar / nonpolar-nonpolar mixtures are …

Miscible (mix)

Polar-nonpolar mixtures are …

Immiscible (do not mix)

What is an unsaturated solution?

Holds less than maximum equilibrium capacity.

What is a saturated solution?

Holds maximum stable solute concentration.

What is a supersaturated solution?

• A solution holding more dissolved solute than normal maximum at that temperature.

• Highly unstable.

“Like Dissolves Like”

Similar intermolecular forces mix.

What do you identify an electrolyte?

Salts and strong acids dissociate fully.

Temperature v. gas solubility

• T increase then S decrease

• T decrease then S increase

Pressure v. gas solubility

• P increases then S increases

• P decreases then S decreases

Henry’s law formula (solubility)

S = (k_H)(P)

Henry’s law formula (concentration)

C_g = (k)(P_g)

What is a mole fraction (X)?

Moles of compound / total moles

Molality (m)

Mol_solute / Kg_solvent

Colligative Properties

• Depends strictly on particle count.

• More electrolytes or particles increase the effects

Vapor Pressure Lowering

• P_solution = (X_solvent)(P_solvent)

• Electrolytes or particles increase then vapor pressure decrease.

Boiling Point Elevation

• ΔT_b = (i)(K_b)(m)

• Electrolytes or particles increase then boiling point increase.

Freezing Point Depression

• ΔT_f = (i)(K_f)(m)

• Electrolytes or particles increase then freezing point decrease.

Osmotic Pressure

• π = (i)(M)(R)(T)

• R = 0.08206

• Electrolytes or particles increase then osmotic pressure increase.

Ideal van 't Hoff (i) calculation …

Total number of moles in product (add coefficients).

Osmosis Flow

Solvent moves toward higher solute concentration.

Isotonic

Equal osmotic pressure with no net movement.

Hypotonic

Lower concentration; solvent leaves the solution.

Hypertonic

Higher concentration; solvent enters the solution.