QiLing Tools

🫙Liquid–Liquid Extraction Calculator - Partition Coefficient, Multiple Extractions, pH and Distribution Ratio

In liquid–liquid extraction a solute distributes between the organic and aqueous phases according to the partition coefficient K_D = c_org / c_aq. Extracting V_aq of aqueous solution once with V_org of solvent leaves a fraction q = V_aq / (V_aq + K_D·V_org) in the water, and n extractions leave qⁿ. With K_D = 4 and 100 mL of water, one extraction with 90 mL leaves q = 100/(100 + 360) = 0.217 (78.3% extracted), while three 30 mL portions leave (100/220)³ = 0.0939 (90.6% extracted) — the classic reason to use several small portions. The tool plots recovery against the number of portions for the same total solvent, shows the n → ∞ limit e^(−K_D·V_org/V_aq), and finds how many extractions reach a target recovery. For weak acids and bases only the neutral form enters the organic phase, so the distribution ratio depends on pH: D = K_D / (1 + 10^(pH − pKa)) for an acid and D = K_D / (1 + 10^(pKa − pH)) for a base. Benzoic acid (pKa 4.20) with K_D = 100 has D ≈ 0.158 at pH 7, so it stays in the water as benzoate. A log D–pH chart gives the pH to extract into the organic layer or back-extract into water. The acid–base separation view computes how ionised benzoic acid, phenol, aniline and naphthalene are in HCl, NaHCO₃ and NaOH washes and explains why bicarbonate comes before hydroxide. Also included: Craig countercurrent distribution (binomial tube distribution, separation factor β = D₁/D₂, resolution) and a separatory-funnel diagram showing which layer is on top from solvent density (dichloromethane 1.33 at the bottom; ether 0.713 and hexane 0.655 on top).

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How to use Liquid–Liquid Extraction Calculator

  1. 1Choose a mode: multiple extractions, pH & distribution ratio, acid–base separation, Craig countercurrent or layer order
  2. 2Enter the partition coefficient, phase volumes and number of portions, or pick a solute, pH or organic solvent
  3. 3Read the recovery, chart, working and recommendations; export charts or copy results

FAQ

Why are several small extractions better than one large one?
One extraction leaves q = V_aq/(V_aq + K_D·V_org) in the water. Splitting the same volume into n portions leaves [V_aq/(V_aq + K_D·V_org/n)]ⁿ, which is always smaller. With K_D = 4, 100 mL of water and 90 mL of solvent in total, one extraction recovers 78.3%, three portions 90.6%, and even infinitely many only approach 1 − e^(−3.6) = 97.3%. The gain shrinks with each extra portion, so about three is typical.
What is the difference between the partition coefficient K_D and the distribution ratio D?
K_D is the concentration ratio of one species (usually the neutral molecule) between the phases and does not depend on pH. D is the ratio of total concentrations of all forms — what you actually measure. For a weak acid HA, the water also holds A⁻, which does not enter the organic phase, so D = K_D/(1 + Ka/[H⁺]). Two pH units below the pKa D ≈ K_D; two units above it D is only about 1% of K_D.
How do you separate benzoic acid, phenol, aniline and naphthalene by extraction?
Dissolve the mixture in ether. Wash with dilute HCl: aniline (conjugate acid pKa 4.6) goes into the water as its salt. Wash with NaHCO₃ (pH ≈ 8.3): benzoic acid (pKa 4.20) becomes sodium benzoate, while phenol (pKa about 10) is only about 2% ionised and stays organic. Wash with NaOH to remove phenol as phenoxide. Naphthalene remains in the ether. Acidify or basify each aqueous extract to recover each compound.
Is the organic layer on top or on the bottom?
Compare densities: lighter than water floats, heavier sinks. Dichloromethane (1.33 g/mL), chloroform (1.49) and carbon tetrachloride (1.59) are on the bottom; diethyl ether (0.713), ethyl acetate (0.902), hexane (0.655) and toluene (0.867) are on top. Saturated brine (about 1.2 g/mL) or heavily loaded layers change the densities, and water-miscible solvents such as ethanol, acetone, acetonitrile and THF cannot be used to extract an aqueous solution.

Features

  • Single vs split extractions with the n → ∞ limit
  • Number of extractions for a target recovery and amount removed per step
  • log D vs pH for weak acids and bases with pH recommendations
  • pKa values shared with the site’s pH calculator (benzoic acid, phenol, aniline, pyridine…)
  • Benzoic acid / phenol / aniline / naphthalene separation scheme with ionisation table
  • Craig countercurrent binomial distribution, separation factor β and resolution
  • Separatory funnel diagram: organic layer on top or bottom by density
  • Export charts as PNG, SVG or CSV