Liquid–liquid extraction – distribution coefficient (partition ratio) In a ternary system of two immiscible liquids and a solute at equilibrium, the ratio of solute concentrations in the two phases is called the distribution coefficient. On what does this coefficient primarily depend?

Introduction / Context:
The Nernst distribution law governs how a solute partitions between two immiscible solvents. This partition ratio, or distribution coefficient, is fundamental for designing extraction stages and predicting required solvent rates.

Given Data / Assumptions:

• Dilute solutions and ideal behavior assumed initially.
• Two immiscible liquid phases in contact at equilibrium.
• Temperature can alter solubility and activity coefficients.

Concept / Approach:
For truly dilute, non-associating systems, the distribution coefficient can be nearly constant, but in real systems it is affected by solute concentration (non-ideal activity effects, dimerization/association) and temperature (changes in solubility parameters and activity coefficients). Therefore, both temperature and concentration influence K_D to varying degrees, and extraction data are typically reported as a function of both variables.

Step-by-Step Solution:

Verification / Alternative check:
Tie-line data in ternary diagrams show K_D varying with composition and shifting with temperature, corroborating the dependence.

Why Other Options Are Wrong:

• Only concentration or only temperature: Incomplete; both exert measurable effects.
• Neither: Contradicts empirical extraction data and thermodynamic models.

Common Pitfalls:
Assuming K_D constant over wide ranges; this can mispredict stage counts. Always consult phase-equilibrium data at the operating temperature and composition.

Final Answer:
both(a) & (b)