# With a partition coefficient how do you decide which solute concentration is the numerator?

Kpc = [X(in solvent A)]/[X(in solvent B)]

I realise that Kpc is actuallly a ratio but when you need the numerical value it has to be treated as a fraction.

When it has to be treated as a fraction how do you decide which solvent is A and which is B?

• In your last sentence, do you mean solvent, and not solute? If you mean solute, then I don't understand the question. – airhuff Mar 5 '17 at 19:23
• @airhuff Thanks for pointing that out. Stupid mistake of mine! – Mirte Mar 8 '17 at 7:49

$$\mathrm{(K_P)_X = \frac{[X](org)}{[X](aq)}}$$