Recrystallization Recovery Calculator
Recrystallization is the most widely used technique for purifying solid organic compounds. The theoretical recovery depends on how much more soluble the compound is at the hot temperature compared to the cold temperature. The formula is: recovery (%) = (S_hot - S_cold) / S_hot x 100, where S_hot and S_cold are the solubilities in g per 100 mL of solvent at the respective temperatures. A high recovery requires a steep solubility curve. Enter the two solubility values and the mass of starting material to calculate theoretical recovery and estimated volume of solvent needed.
Recrystallization recovery formula
Recovery (%) = (S_hot - S_cold) / S_hot x 100
Mass recovered = crude mass x (recovery / 100)
Solvent volume (mL) = crude mass x 100 / S_hot
The formula assumes you dissolve the crude solid in exactly the minimum volume of hot solvent (saturated solution at hot temperature), then cool to a temperature where solubility is S_cold. The fraction of compound remaining in solution after cooling equals S_cold / S_hot.
Improving recrystallization recovery
- Use the minimum amount of hot solvent to avoid excess dissolution losses.
- Cool slowly to favour large crystal formation, which filters more cleanly.
- Seed with pure crystals of the compound to initiate crystallization at higher temperature.
- Collect mother liquors; a second recrystallization recovers more material.
- If recovery is below 70%, consider a different solvent with a steeper solubility curve.
Recrystallization recovery: frequently asked questions
How does recrystallization purify compounds?
Recrystallization works by dissolving the crude solid in a minimum of hot solvent, then cooling to reduce solubility. The target compound crystallizes out while impurities (which are present in small amounts) remain in solution. The key requirement is that solubility differs significantly between hot and cold temperatures.
What is the recrystallization recovery formula?
Theoretical recovery (%) = (S_hot - S_cold) / S_hot x 100, where S_hot is the solubility at the hot temperature (g per 100 mL solvent) and S_cold is the solubility at the cold temperature. This assumes you dissolve just enough to make a saturated solution at the hot temperature.
Why is actual recovery always lower than theoretical?
Actual recovery is lower because: some compound remains dissolved in the cold filtrate (mother liquors) at its cold solubility; mechanical losses occur during filtration; crystals may adhere to glassware; and the solution may not be exactly saturated at the hot temperature if excess solvent was used.
What makes a good recrystallization solvent?
A good solvent has high solubility for the compound at high temperature, low solubility at low temperature (steep solubility curve), and easy removal from the crystals (low boiling point or volatility). The impurities should be either very soluble (stay in solution) or insoluble (removed by hot filtration).
How do I calculate the volume of solvent needed?
Dissolve the crude material in the minimum hot solvent: V (mL) = mass of compound (g) x 100 / S_hot. For example, if S_hot = 20 g/100 mL and you have 5 g, you need 5 x 100/20 = 25 mL hot solvent to make a just-saturated solution.
Official sources
- NIST Chemistry WebBook: Solubility data for organic compounds.
- ACS: ACS Publications (Organic Process Research and Development).
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.