Latest about Chromatography and Sublimation 2022 | Basic Concept of Chromatography and Sublimation | What is Chromatography and Sublimation

SUBLIMATION

The process of direct conversion of a solid into vapours by heating without passing through the liquid phase is called sublimation.

The vapours can be condensed to form the solid again. Sublimation is used to purify solid substances. The substance obtained after sublimation is called sublimate. The impure substance, which is sublimed, is called sublimated.

Examples:

iodine, NH, Cl, naphthalene, anthracene, benzoic acid etc.

 Method:

The impure substance is taken on a watch glass.

It is covered with an inverted funnel having a cotton plug into its stem.

The funnel is cooled with wet cotton.

The substance is heated slowly in a sand bath.

The pure solid deposits on the inner cold side of the funnel.

SOLVENT EXTRACTION

The process of obtaining a substance from a solution with the help of an immiscible solvent is called solvent extraction.

Principle

Solvent extraction is based upon Distribution Law.

A solute can be separated from a solution by an immiscible solvent. The desired solute is more soluble in the solvent than the solution.

Practically, the solution and the solvent are placed in a separating funnel. The funnel is stoppered and the two liquids are shaken together.

Thus, the solute will move from the solution to the added solvent layer. This layer can be separated. The solute can be obtained by evaporating the solvent.

Example:

Ether extraction is a commonly used laboratory solvent extraction. It is mainly used to separate organic compounds from water.

Method

The aqueous solution containing an organic compound is shaken up with ether in a separating funnel.

The organic compound will move from the water layer to the ether layer. The inorganic impurities remain in an aqueous layer.

The ether layer is separated from the separating funnel.

Ether is then evaporated to get the pure organic compound.

Repeated extractions using smaller portions of solvent are more effective than single extraction with the volume of solvent.

This techniquebeneficialeful to obtain a product which is volatile or thermally unstable. Such products are difficult to obtain by other techniques.

CHROMATOGRAPHY

It is an analytical technique used for the separation of a mixture, due to the different distribution of substance between a stationary phase and a mobile phase.

Origin of Name

Chromatography is derived from the Greek word “Khromatos”, meaning “Colour writing”.

Stationary Phase

It may be a solid or a liquid supported on an inert solid.

Examples: Silica gel, water adsorbed in paper etc.

Mobile Phase

It may be a liquid or a gas. It flows over the stationary phase.

Examples: Ethanol, Acetone, Hexane etc.

Principle

It is based upon distribution law.

The mixture is allowed to come in contact with two phases, a stationary phase and a mobile phase. Different The distribution of the component between two phases is controlled by distribution coefficient K given as components have different affinities for the stationary phase and mobile phase due to which they are separated.

K = concentration of a component in the mobile phase/concentration of a component in the stationary phase

Hence, a Compound with a smaller K value remains in the stationary phase.

While a Compound with a larger K value goes with the mobile phase

Classes of Chromatography

Chromatography is divided into many classes. Two important classes of chromatography are

(1) Adsorption chromatography

(2) Partition chromatography

Adsorption Chromatography

In this chromatography, the stationary phase is a solid. When the mobile phase flows over the stationary phase, substances leave the mobile phase and are adsorbed on the stationary phase.

Partition Chromatography

In partition chromatography, the stationary phase is a liquid, supported on an inert solid. In this, a substance distributes itself between the mobile phase and the stationary phase.

For each class of chromatography, many methods can be used. e.g. Paper Chromatography

Paper Chromatography

It is a method of partition chromatography. It has

Chromatography
Chromatography

Stationary Phase:

A liquid (usually H₂O) is adsorbed on paper. The adsorbed liquid behaves as the immiscible liquid in the mobile phase

Mobile Phase:

A liquid passes over the adsorbed liquid in the paper. It is usually an organic liquid e.g. ethanol, acetone etc.

Paper chromatography can be done in many ways

(1) Ascending        (2) Descending        (3) Radial / Circular

Ascending Paper Chromatography

In this method, the solvent is placed at the bottom of a vessel. A paper is suspended in it. The solvent moves upward by capillary action.

Uses of Chromatography

□  It is useful in organic synthesis. It is to separate, isolate and purification of substances from a mixture.

□  It is used for qualitative and quantitative analysis.

□  It is used to determine the purity of a substance.

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