Partition Coefficient Calculator

Calculator

Choose a mode, enter values, and compute instantly.

Mode

Switch modes to reveal the matching inputs.

Organic concentration

Equilibrium concentration in organic phase.

Aqueous concentration

Equilibrium concentration in aqueous phase.

Concentration unit

Use the same unit for both phases.

Partition coefficient (K)

K = C_org / C_aq.

Organic concentration (optional)

Aqueous concentration (optional)

Concentration unit

Partition coefficient (K)

Higher K usually increases extraction into organic.

Aqueous volume

Volume of the aqueous phase.

Organic volume (each extraction)

Use per-stage volume for multiple extractions.

Input basis

Pick how you want to define the starting solute.

Initial amount (aqueous)

Used directly in mass balance output.

Initial concentration (aqueous)

Amount is estimated as C0 × V_aq.

Number of extractions (n)

Uses fresh organic solvent each stage.

Input type

logP is log10(K) for the neutral species.

K (neutral)

logP

pH

pKa

Use the pKa for the ionizable group of interest.

Species model

Applies a simple unionized fraction approximation.

Reference K

Reference temperature (°C)

Target temperature (°C)

ΔH (kJ/mol)

Sign matters: positive ΔH often increases K with temperature.

Reset

Example data

Sample inputs and typical outputs for quick validation.

Scenario	Inputs	Outputs
Compute K	C_org=12 mg/L, C_aq=3 mg/L	K=4, log10(K)=0.6021
Single extraction	K=4, V_aq=1 L, V_org=0.25 L, m0=100 mg	Remaining=50 mg, Extracted=50 mg, 50%
logD (weak acid)	logP=2, pH=7.4, pKa=4.0	D≈0.0398, logD≈−1.40, f_un≈0.000398

Examples are rounded and assume dilute solutions at equilibrium.

Formula used

Core relations behind each mode.

Partition coefficient: K = Corg / Caq (same units ⇒ unitless ratio).
From K: Corg = K × Caq and Caq = Corg / K.
Single extraction: m_aq = m0 / (1 + K·Vorg/Vaq).
n extractions: m_aq,n = m0·(Vaq/(Vaq + K·Vorg))^n (fresh organic each stage).
Distribution coefficient: D = K × fun, where fun is the unionized fraction.
Weak acid: fun = 1/(1 + 10^(pH − pKa)); Weak base: fun = 1/(1 + 10^(pKa − pH)).
Log values: logP = log10(K) and logD = log10(D).
Temperature shift: ln(K2/K1)=-(ΔH/R)·(1/T2 − 1/T1) with T in Kelvin.

How to use this calculator

A quick workflow for clean results.

Select the mode that matches your experiment or need.
Enter values using consistent units within a given mode.
For extraction, set volumes per stage and choose n.
For D, provide pH, pKa, and acid or base model.
Press Submit to show results above the form.
Use the CSV or PDF buttons to export your last run.

Tip: K and D are most reliable for dilute solutions and stable temperature.

Nernst Distribution Law in Practice

The partition coefficient K expresses how a neutral solute distributes between two immiscible phases at equilibrium: K = Corg/Caq. When concentrations share units, K is unitless. Values below 1 indicate aqueous preference, while values above 10 usually signal strong organic affinity. In practice, shake‑flask experiments often use low solute levels to stay in the linear, dilute regime.

Reading logP and logD Together

logP is log10(K) for the neutral form, commonly reported for the octanol–water system. Many drug‑like compounds fall near logP 0–3, while logP above 3 often correlates with higher membrane affinity and lower aqueous solubility. logD extends this idea to a chosen pH by scaling K with the unionized fraction. For a weak acid, increasing pH above pKa decreases D; for a weak base, lowering pH below pKa decreases D.

Extraction Efficiency and Volume Ratios

For liquid–liquid extraction, performance depends on the phase‑volume ratio and K. Define R = K·Vorg/Vaq. For one extraction, the fraction extracted is R/(1+R); the fraction remaining is 1/(1+R). Multiple smaller extractions can outperform one large extraction because the remaining fraction becomes (Vaq/(Vaq+K·Vorg))^n. For example, with K=4 and Vorg/Vaq=0.25, one extraction removes 50%, while two stages remove 75%.

Controlling Temperature and Solvent Choice

K is sensitive to temperature and solvent composition because activity coefficients change. The van’t Hoff approximation uses ln(K2/K1)=-(ΔH/R)(1/T2−1/T1), with T in Kelvin and R the gas constant. Keep temperatures stable, pre‑equilibrate phases, and record solvent grades to improve reproducibility. Small water content in the organic phase can shift K, so allow adequate settling time and avoid vigorous foaming.

Data Checks Before You Export

Good practice is to confirm equilibrium (consistent K across repeats), avoid emulsions, and ensure phase volumes are measured after separation. Report the solvent pair, temperature, pH (for D), and units used for Corg and Caq. Include replicate averages, standard deviation, and any blank subtraction if analytical detection has background. Exporting CSV or PDF helps preserve these details alongside computed K, logP, logD, and extraction yield.

FAQs

Common questions about partition and distribution calculations.

1) What is the partition coefficient in this calculator?

It is K = Corg/Caq at equilibrium for a neutral solute. Enter matched concentration units for both phases to keep K unitless and directly comparable across runs.

2) How is logP different from logD?

logP is log10(K) for the neutral species. logD is log10(D) at a chosen pH, where D accounts for ionization using an estimated unionized fraction from pH and pKa.

3) Which concentration goes in the numerator?

This tool uses organic over aqueous (Corg/Caq). If you use the opposite convention elsewhere, take the reciprocal before comparing values.

4) Why do multiple extractions often work better?

Each stage uses fresh organic solvent, so the remaining fraction multiplies across stages. Even with the same total organic volume, splitting it can increase overall recovery.

5) Can I use any concentration units?

Yes. Use any consistent unit set within a mode (e.g., mg/L in both phases). For extraction with concentration input, the implied amount is C0 × Vaq.

6) How does temperature affect K?

K can change because solvation and activity coefficients change with temperature. The van’t Hoff mode estimates the shift from K1 to K2 using an enthalpy term, assuming ΔH stays roughly constant.