Methods of Purification

Simple Distillation

Simple distillation involves heating a mixture and collecting the vapor that is produced, followed by cooling and collecting the distillate. It’s used for separating a liquid from a solution.
In this method, the substance with the lower boiling point vaporizes first. It is then cooled back into a liquid in the condenser and collected.
However, simple distillation is not suitable for mixtures where the boiling points of the components are close to each other.

Fractional Distillation

Fractional distillation is used for separating a mixture of liquids with different boiling points.
A fractionating column is used, which enables a series of separate distillations to occur at the same time.
The substance with the lowest boiling point evaporates first, condenses on the fractionating column, then drains back into the flask. This process, known as reflux, helps to ensure a complete separation.

Filtration

Filtration is used to separate solids from liquids, particularly when the solid does not dissolve in the liquid.
A porous material such as filter paper is used, which allows the liquid to pass through but not the solid particles.
Ensure the filter paper is folded properly, covering all edges of the funnel, to prevent any solid passing through.

Crystallization

Crystallization involves evaporating a solvent to leave a solid product. It is ideal for solid-liquid mixtures where the solid is soluble in the liquid.
As the solution cools, the solution becomes saturated causing the solid to form crystals.
The crystals can be separated from the remaining solution by filtration.

Chromatography

Chromatography is a method used to separate components of a mixed substance based on the movement of different substances up a chromatography paper.
A drop of the mixture is placed on the paper, which is then put in a suitable solvent.
The components of the mixture move up the paper at different rates, resulting in them being spaced apart on the paper.
The substances are identified by comparing the distance moved with reference substances under the same conditions.

Calculations Related to Purification Methods

Be familiar with calculations involving percentages and ratios in the context of purity.
Understand how to calculate the Rf value (the ratio of the distance travelled by a compound to the distance travelled by the solvent) in chromatography.
Grasp the concept of percentage yield and how it is calculated and interpreted. This is a measure of how much product is obtained compared to the maximum that could theoretically be produced.