Pharmaceutics: Miscibility of Liquids

Phase Changes in Immiscible Liquids

• A and B are partially miscible liquids, and their mixture forms two liquid phases below a certain temperature and one liquid phase above that temperature.
• The phase changes observed when A is continually added to B at a temperature of:
  • 25°C: a single liquid phase up to 31% w/w A in B, 2 liquid phases from 31% A in B to 78% A in B, and a single phase is retained as A is further added.
  • 45°C: a single phase exists for all combinations of A and B since the temperature is above the region of immiscibility.

Phase Compositions and Weights

• A mixture containing A (20g) and B (30g) prepared at 22°C:
  • Compositions of the 2 phases: 30% w/w A and 70% w/w B; 80% w/w A and 20% w/w B.
  • Weights of each phase: approximately 40g and 10g.
• Ten grams of a mixture containing equal weights of A and B at 50°C cooled to 10°C:
  • Phase change observed at 34°C.
  • At 10°C, 12.5g of B needs to be added to produce a single phase, and 87.5g of A needs to be added to produce a single phase.

Phenol-Water System

• A phenol-water system at 50°C with a total composition of 24% phenol in water:
  • Respective concentrations of the 2 layers: 11% and 63% phenol in water.
  • Weight of the aqueous layer: 7.5g.
  • Weight of the phenolic layer: 2.5g.
  • Weight of phenol in the aqueous layer: 0.825g.
  • Weight of water in the aqueous layer: 6.675g.
  • Weight of phenol in the phenolic layer: 1.575g.
  • Weight of water in the phenolic layer: 0.925g.

Effect of KCl on the Phenol-Water System

• Addition of 0.1 mole of KCl decreases the mutual solubility of phenol and water by 10%:
  • New points: 9.9 and 66.7.
  • Weight of the aqueous layer: 7.52g.
  • Weight of the phenolic layer: 2.48g.

Another Phenol-Water Mixture

• A phenol-water mixture at 20°C with a total composition of 50% phenol in water:
  • Respective concentrations of the 2 layers: 8.4 and 72.2% phenol.
  • Weight of the aqueous layer: 174g.
  • Weight of the phenolic layer: 326g.
  • Weight of phenol in the phenolic layer: 235.4g.
  • Weight of phenol in the aqueous layer: 14.6g.

Yet Another Phenol-Water Mixture

• A mixture containing 21% by weight of phenol in water prepared at 30°C:
  • Liquid phases that separate contain 7% and 70% by weight of phenol respectively.
  • Total weight of the original mixture: 135g.
  • Weight of the aqueous layer: 105g.
  • Weight of the phenolic layer: 30g.
  • Weight of water in the aqueous layer: not specified.
  • Weight of water in the phenolic layer: not specified.