Chapter 1: Solutions

Gaseous Solutions

• Gas-Gas: Mixture of O2 and N2
• Liquid-Gas: Chloroform with N2
• Solid-Gas: Camphor in N2

Liquid Solutions

• Gas-Liquid: O2 dissolved in water
• Liquid-Liquid: Ethanol dissolved in water
• Solid-Liquid: Glucose dissolved in water

Solid Solutions

• Gas-Solid: H2 in Pd
• Liquid-Solid: Amalgam of Hg with Na
• Solid-Solid: Cu dissolved in gold

Important Formulas

Normality = (No. of gram equivalent of solute x 1000) / Volume of solution (in mL) Molality (m) = (No. of moles of solute x 1000) / Mass of solvent (in g) Molarity (M) = (No. of moles of solute x 1000) / Volume of solution (in mL)

Solid in Liquid

• Effect of Temperature: Endothermic (Δsol H > 0) solubility increases with increasing T. Exothermic (Δsol H < 0) solubility decreases with increasing T.
• Effect of Pressure: Not significant effect.

Gas in Liquid

• Effect of Temperature: Solubility increases with decrease in temperature.
• Effect of Pressure: Solubility increases with increase in pressure.

Henry's Law

Partial pressure of gas in vapour phase (p) is proportional to the mole fraction of gas (x) in the solution.

p = KH · x

Higher the value of KH, lower the solubility.

Liquid-Liquid Solutions (Raoult's Law)

• Raoult's law: p1 = p1°x1
• Dalton's law of partial pressure: P(Total) = p1 + p2 + ... pn
• In vapour phase: y1 = p1 / P(Total)

Ideal Solutions

• Obey Raoult's law
• ΔH(mix) = 0, ΔV(mix) = 0
• Interactions A-A and B-B = A-B
• Example: n-hexane and n-heptane, Ethyl bromide + Ethyl chloride

Non-Ideal Solutions

• Do not Obey Raoult's law (ΔH(mix) ≠ 0 and ΔV(mix) ≠ 0)
• Positive Deviation: ΔH > 0, ΔV > 0. Interactions A-B < A-A or B-B. Example: Acetone + Ethyl alcohol, Water + Ethyl alcohol.
• Negative Deviation: ΔH < 0, ΔV < 0. Interactions A-B > A-A or B-B. Example: Acetone + Aniline, Acetone + Chloroform.

Azeotropes

The mixtures of liquids which boil at constant temperature like a pure liquid and possess same composition of components in liquid as well as binary vapour phase are called constant boiling mixtures or azeotropic mixtures.

• Minimum boiling azeotropes: Formed by liquid pairs which show positive deviations (Ex: Ethanol-Water mixture).
• Maximum boiling azeotropes: Formed by liquid pairs which show negative deviations (Ex: Nitric Acid-Water mixture).

Types & Formulas

• Relative lowering of vapour pressure: (P1° - P1) / P1° = x2 = n2 / (n1 + n2)
• Elevation of boiling point: ΔTb = Kb × m = (Kb × 1000 × W2) / (M2 × W1)
• Depression in freezing point: ΔTf = Kf × m = (Kf × 1000 × W2) / (M2 × W1)
• Osmotic pressure: π = CRT

Osmosis Deep Dive

• Osmosis: Flow of solvent molecules from pure solvent to solution through a semi permeable membrane.
• Osmotic pressure: Excess pressure that must be applied to a solution to prevent osmosis.
• Isotonic Solutions: Solutions with same osmotic pressure.
• Hypertonic Solution: Water flows out of cell, and cell shrinks.
• Hypotonic Solutions: Water flows into the cells and the cell swells.
• Reverse Osmosis: The process of movement of solvent through a semi-permeable membrane from the solution to pure solvent by applying pressure more than osmotic pressure.