Solutions and Solubility

• A solution is a homogeneous mixture of two or more components.
• Molarity is the number of moles of solute in one liter of solution.
• Molality is the number of moles of solute in 1 kg of solvent.
• The mole fraction is the ratio of moles of one component to the total moles of all components in the solution.

Solubility

• Solubility is the maximum amount of a substance that can dissolve in a specific amount of solvent at a specific temperature and pressure.
• Solubility is affected by the nature of the solute and solvent, as well as the temperature and pressure.
• Polar solutes dissolve in polar solvents, and non-polar solutes dissolve in non-polar solvents due to similar intermolecular forces.
• If dissolution is exothermic, solubility decreases as temperature increases.
• Gas dissolution in liquids is an exothermic process.
• As temperature increases, the equilibrium shifts in reverse, decreasing the solubility of gas in a liquid.

Henry's Law

P = KH X, where P is the partial pressure of gas in the vapor phase and X is the mole fraction of the gas

Raoult's Law

• The partial vapor pressure of any component is proportional to its mole fraction (PA = PXA).
• Raoult's Law becomes a special case of Henry's Law when KH equals P.

Ideal Solutions

• Ideal solutions obey Raoult's Law at all concentrations and temperatures.
• In ideal solutions, A-A and B-B interactions equal A-B interactions.

Non-Ideal Solutions

• Non-ideal solutions do not obey Raoult's Law.
• In non-ideal solutions, A-A or B-B interactions differ from A-B interactions.
• Non-ideal solutions with a positive deviation have higher vapor pressure than expected due to decreased intermolecular forces.
• Non-ideal solutions with a negative deviation have lower vapor pressure than expected due to increased intermolecular forces.

Azeotropic Mixtures

• Azeotropes are binary mixtures with the same composition in liquid and vapor phases that boil at a constant temperature.
• Components forming an azeotrope cannot be separated by fractional distillation but can be separated by azeotropic distillation.

Colligative Properties of Dilute Solutions

• Colligative properties depend on the number of solute particles, not their nature.

Relative Lowering in Vapor Pressure

• The vapor pressure of a solution with a non-volatile solute is lower than that of the pure solvent.
• Formula: (P-P)/P = (W2 * M₁) / (M₂ * W₁), where P is vapor pressure of the pure solvent, P is vapor pressure with solute, W₂ is solute weight, M₁ is solvent molecular weight, M₂ is solute molecular weight, and W₁ is solvent weight.

Elevation in Boiling Point

• The boiling point of a solution with a non-volatile solute increases.
• ΔT = K * (1000 × W₂) / (M₂ × W₁), where ΔT is the boiling point elevation, K is the ebullioscopic constant.

Depression in Freezing Point

ΔTf = Kf * (1000 × W₂) / (M₂ × W₁), where ΔTf is the freezing point depression and Kf is the cryoscopic constant.

Osmosis and Osmotic Pressure

• Osmosis is the flow of solvent molecules through a semipermeable membrane from a solvent to a solution or from a dilute to a concentrated solution.
• Osmotic pressure (π) is the external pressure needed to stop the solvent flow into the solution.
• Formula: π = CRT, where C is the concentration, R is the gas constant, and T is the temperature.

Isotonic, Hypertonic, and Hypotonic Solutions

• Isotonic solutions have the same osmotic pressure.
• Hypertonic solutions have a higher concentration.
• Hypotonic solutions have a lower concentration.

Reverse Osmosis

• Applying pressure greater than osmotic pressure reverses the solvent flow, moving it from the solution to the pure solvent.
• Reverse osmosis is used for seawater desalination.

Abnormal Molar Mass

• Abnormal molar masses are higher or lower than expected.
• van't Hoff factor (i) = observed colligative properties / calculated colligative properties

van't Hoff factor (i)

• If i = 1, there is neither dissociation nor association.
• If i > 1, dissociation occurs.
• If i < 1, association occurs.
• Dissociation occurs in solutes like NaCl, KCl, and BaCl₂.
• Association occurs in solutes like CH3COOH and PhCOOH in benzene.
• α = i-1/n-1, for dissociation. Formula: ΔΤ = Κ Χ(1000×W2)/(M₂ x W₁)
• α = i-1/1/n-1, for association.

Applications

CaCl₂ reduces snow by depressing the freezing point.

• Ethylene glycol is mixed with radiator water to lower the freezing point.
• Helium-oxygen mixtures are used by deep-sea divers due to low blood solubility.

Understand solutions as homogeneous mixtures and key concentration terms like molarity, molality, and mole fraction. Explore factors affecting solubility, including solute-solvent nature, temperature, and pressure. Learn Henry's Law regarding gas solubility in liquids.