25.2.2—And use a partition coefficient for a system

For a solute in the same physical state in two immiscible solvents, Kpc = concentration in solvent 1 divided by concentration in solvent 2 at equilibrium.

State the numerator solvent, use matched units and measure after the two phases have equilibrated. If the solute associates or reacts in one phase, the simple expression may not apply.

If [solute]organic=0.80 mol dm⁻³ and [solute]aqueous=0.20 mol dm⁻³, Kpc(organic/aqueous)=4.0.

Do not invert the ratio without changing the label, and do not calculate from initial concentrations before equilibrium.