Purification and Separation Techniques in Organic Chemistry

Vocabulary flashcards covering the purification and separation techniques of organic compounds, including sublimation, crystallisation, distillation methods, differential extraction, and various chromatography types.

Sublimation

A purification technique based on heating solid substances that change directly from solid to vapour state without passing through the liquid state, used to separate sublimable compounds from non-sublimable impurities.

Crystallisation

A purification technique for solid organic compounds based on the difference in solubilities of the compound and impurities in a suitable solvent, where the compound is sparingly soluble at room temperature but appreciably soluble at higher temperature.

Mother Liquor

The filtrate obtained after cooling a nearly saturated solution and filtering off the crystallised pure compound, containing impurities and a small quantity of the compound.

Simple Distillation

A technique used to separate volatile liquids from nonvolatile impurities and liquids having sufficient difference in their boiling points, such as chloroform (b.p. $334\,\text{K}$) and aniline (b.p. $457\,\text{K}$).

Fractional Distillation

A distillation technique used to separate liquids when the difference in their boiling points is small, wherein vapours are passed through a fractionating column before condensation.

Theoretical Plate

Each successive condensation and vaporisation unit provided within a fractionating column.

Distillation Under Reduced Pressure

A method used to purify liquids that have very high boiling points or that decompose at or below their boiling points by reducing the external surface pressure with a water pump or vacuum pump so they boil at a lower temperature.

Steam Distillation

A technique applied to separate substances that are steam volatile and immiscible with water, in which the liquid mixture boils when the sum of the vapour pressures of the organic liquid ($p_1$) and water ($p_2$) equals atmospheric pressure ($p = p_1 + p_2$).

Differential Extraction

A separation method in which an organic compound dissolved in an aqueous medium is separated by shaking it in a separatory funnel with an immiscible organic solvent in which it is more soluble.

Continuous Extraction

An extraction technique employed when an organic compound is less soluble in the organic solvent, requiring the same solvent to be repeatedly cycled and used to extract the compound.

Chromatography

A technique (named from the Greek word 'chroma', meaning colour) extensively used to separate mixtures into their components, purify compounds, and test the purity of compounds.

Stationary Phase

The fixed solid or liquid phase onto which a mixture of substances is applied in chromatography.

Mobile Phase

The moving phase, consisting of a pure solvent, a mixture of solvents, or a gas, that is allowed to move slowly over the stationary phase in chromatography.

Adsorption Chromatography

A chromatographic technique based on the fact that different compounds are adsorbed on an adsorbent (commonly silica gel or alumina) to different degrees.

Column Chromatography

A type of adsorption chromatography that involves the separation of a mixture over an adsorbent packed as a stationary phase in a glass tube fitted with a stopcock at its lower end.

Thin Layer Chromatography (TLC)

An adsorption chromatographic technique involving the separation of substances of a mixture over a thin layer (about $0.2\,\text{mm}$ thick) of an adsorbent coated on a glass plate.

Chromaplate

A glass plate coated with a thin layer (about $0.2\,\text{mm}$ thick) of an adsorbent, such as silica gel or alumina, used in thin layer chromatography.

Retardation Factor ($R_f$ Value)

A ratio expressing the relative adsorption of each component in thin layer chromatography, defined as: $R_f = \frac{\text{Distance moved by the substance from base line (x)}}{\text{Distance moved by the solvent from base line (y)}}$.

Ninhydrin Solution

A spray reagent used to detect colourless spots of amino acids on a developed thin layer chromatography plate.

Partition Chromatography

A chromatography technique based on continuous differential partitioning of components of a mixture between stationary and mobile phases.

Paper Chromatography

A type of partition chromatography that uses special chromatography paper containing trapped water as the stationary phase and a solvent moving by capillary action as the mobile phase.

Chromatogram

The developed paper strip or plate displaying separated components of a mixture at different positions or heights.