The solvent front is the furthest distance the solvent travels along the stationary phase during chromatography.

The sample line is where the sample undergoing chromatography is placed on the stationary phase.

The Rf value is a ratio describing the distance a component of a sample travelled, in relation to the distance the solvent travelled under the same conditions.

A chromatogram is the resultant pattern on the stationary phase after chromatography has been carried out.

Chromatography: separating a mixture of inks

Combined science

Separating mixtures (including formulations)

Solutions

Filtration

Crystallisation

Chromatography: paper

Interpreting chromatograms

Distillation: simple distillation

Distillation: separating a mixture of inks

Distillation: fractional distillation

Potable water

Wastewater treatment

Water sample analysis: pH

Water sample analysis: dissolved solids

Water sample analysis: distillation

In the Making Salts unit, pupils will build on their understanding of separation techniques to learn about the process of making salts and writing balanced chemical equations.

In the Separation Techniques unit, pupils learned about various methods for separating mixtures, including filtration, evaporation, distillation, and chromatography.

This unit explores purification techniques, including filtration, crystallisation, and distillation. It explains formulations, uses chromatographic methods to identify pure and impure substances, and interprets chromatograms with Rf values. The emphasis is on accurate measurements.

Separating substances

Physical activity and equipment requiring safe use

True or false? Rf values can be calculated from a chromatogram of unknown samples. These Rf values can be compared against sample data to identify unknown substances.

Which of these does not need to remain constant for a fair comparison of Rf values between two chromatograms?

the substance will move with the solvent front

the substance will have an Rf value above 1

the substance will stay at the sample line

the substance will have a negative Rf value

If a substance is insoluble in the chosen solvent, which of the following would happen?

What is the Rf value of a solvent front that travels 8.0 cm and a substance spot that travels 20 mm?

True or false? The temperature does not affect the outcome of the chromatography process.

A chromatogram is collected and two different substances have similar Rf values. What might have caused this? They must have similar {{}} in the solvent used.

Which of the following is **not** part of preparing a chromatography paper?

pencil marks do not travel with the solvent

pencil reacts with the inks to help them separate

Why do we use pencil to draw the sample line in chromatography?

What is the purpose of the stationary phase in chromatography?

True or false? The solvent front should be marked after the paper is removed from the container.

True or false? If two substances have the same Rf value then they must be the same substance.

Calculate the Rf value of a spot that travels 55 mm up from the sample line, where the chromatogram shows a solvent front of 86 mm. 

Chromatography: separating a mixture of inks

Lesson outcome

Content guidance