How does paper chromatography work for separating coloured substances?

Paper chromatography works by separating coloured substances based on their different solubilities and rates of absorption in a solvent.

In more detail, paper chromatography is a method used to separate mixtures into their individual components. It is particularly effective for separating coloured substances such as inks, dyes or pigments. The process involves a piece of paper, often filter paper, which acts as the stationary phase, and a solvent, which acts as the mobile phase.

The mixture to be separated is applied as a spot near one end of the paper. The paper is then placed in a container with the solvent. The solvent is absorbed by the paper and moves up, carrying the components of the mixture with it. As the solvent rises through the paper, it meets the sample mixture, which starts to travel up the paper with the solvent.

Different substances in the mixture will move at different rates depending on their solubility in the solvent and their attraction to the paper. Substances that are more soluble in the solvent and less attracted to the paper will travel further up the paper, while those that are less soluble and more attracted to the paper will not travel as far. This results in the separation of the substances along the paper.

Once the solvent has nearly reached the top of the paper, it is removed from the container and the paper is allowed to dry. The separated substances can then be visualised, often appearing as distinct coloured spots or bands on the paper. The distance travelled by each substance can be measured and compared to help identify the substances present in the mixture. This technique is widely used in laboratories to analyse the components of complex mixtures.