1. Raoult’s Law in One Line 🧪

For any component 1 in a liquid solution:

\(p_1 = x_1\,p_1^{0}\)  :contentReference[oaicite:8]{index=8}

2. Ideal Solutions 👍

  • Definition: They follow Raoult’s law for every composition.
  • No heat or volume change: \( \Delta_{\text{mix}}H = 0 \) and \( \Delta_{\text{mix}}V = 0 \) 🔥➖📏:contentReference[oaicite:9]{index=9}
  • Molecular view: A–A, B–B, and A–B attractions stay almost equal, so nothing “new” happens between molecules.
  • Classic pairs: n-hexane + n-heptane, bromoethane + chloroethane, benzene + toluene.:contentReference[oaicite:10]{index=10}

3. Non-Ideal Solutions 👎

They break Raoult’s rule somewhere along the line. Two flavors appear:

3.1 Positive Deviation (vapour pressure rises) 🚀

  • A–B attractions weaken compared with A–A or B–B.
  • Molecules escape easily → higher vapour pressure.
  • Examples: ethanol + acetone, carbon disulphide + acetone.:contentReference[oaicite:11]{index=11}

3.2 Negative Deviation (vapour pressure falls) 🌧️

  • A–B attractions strengthen (extra hydrogen bonding or dipole bonds).
  • Molecules hold tighter → lower vapour pressure.
  • Examples: phenol + aniline, chloroform + acetone.:contentReference[oaicite:12]{index=12}

4. Azeotropes — The Un-separable Mix 🌀

  • Binary mixture that boils at a constant temperature with identical liquid & vapour composition.
  • Minimum-boiling azeotrope: Large positive deviation, e.g. 95 % (v/v) ethanol + water.:contentReference[oaicite:13]{index=13}
  • Maximum-boiling azeotrope: Large negative deviation, e.g. 68 % HNO3 + 32 % H2O (393.5 K).:contentReference[oaicite:14]{index=14}

5. Why Do Deviations Happen? 💡

  • Positive deviation: Adding solute breaks stronger self-bonds → easier escape.
  • Negative deviation: New cross-bonds form and “lock” molecules in place.

High-Yield Ideas for NEET 🏆

  1. Remember \(p_1 = x_1\,p_1^{0}\) and what a straight-line vapor-pressure graph means.
  2. Zero heat/volume change marks an ideal solution — quick check question!
  3. Link positive vs negative deviation to strength of A–B interactions.
  4. Minimum vs maximum boiling azeotropes and their classic examples.
  5. Connect molecular interactions (hydrogen bonding, dipole forces) with observed macroscopic behavior.