A mixture is a material that contains two or more different substances that can be physically separated.

In chemistry, to separate something is to extract and isolate a substance from a mixture.

A property is a feature or characteristic of a substance that can be used to classify it or describe how it behaves.

Separating mixtures

Chemistry

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

A solute is a substance that has dissolved into a solvent.

A solvent is a liquid into which a solute dissolves.

When a substance dissolves in a solvent, it is described as soluble in that solvent.

A substance that does not dissolve in a particular solvent is described as insoluble.

A state symbol is used in chemical equations to indicate the physical state of a substance.

Solutions

Filtration is a technique to separate insoluble solids from a liquid by passing the mixture it is in through a filter.

A filtrate is the liquid component separated from a mixture as a result of filtration.

The insoluble component collected in the filter paper as a result of filtration is called the residue.

A component refers to a part of something, e.g. a tyre on a car.

Filtration

A saturated solution is one in which no more solute can dissolve in the solvent at a given temperature.

Crystallisation is a process that forms solid crystals from a saturated solution by continued removal of the solvent (e.g. evaporation).

When a substance dissolves in a liquid, it is described as soluble in that liquid.

Crystallisation

Chromatography is a technique that separates the components of a mixture, and the results can be analysed.

The mobile phase is the movement of a solvent and any dissolved components of a sample along the stationary phase in chromatography.

The stationary phase is a surface along which the solvent (and any dissolved components) travels. It does not move during chromatography.

A chromatogram is the resultant pattern of a sample’s components on the stationary phase after chromatography has been carried out.

Chromatography: paper

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 the retention factor - 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.

Interpreting chromatograms

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.

Chromatography: separating a mixture of inks

Boiling occurs when a substance in the liquid state is heated and changes to the gas state with gas bubbles formed.

Condensation is the process by which a substance in the gas state is cooled and changes to a liquid state.

Distillation is a separation technique that uses boiling and condensation to remove and isolate a liquid component of a mixture.

A condenser is a piece of apparatus composed of a tube surrounded by a cold layer, usually cold water.

A distillate is the condensed component that has been isolated during distillation.

Distillation: simple distillation

a part of something, e.g. a tyre on a car

a separation technique that uses boiling and condensation to remove and isolate a liquid component of a mixture

a thin tube used to transfer (i.e. "deliver") a substance (usually in the gas state) from one container to another

a piece of apparatus composed of a tube surrounded by a cold layer, usually cold water

the liquid that is condensed from the gas state during distillation

Distillation: separating a mixture of inks

A fraction is a component of a mixture that has been separated by fractional distillation.

Fractional distillation is a method used to separate miscible fluids (liquids or gases) with different boiling points into individual components (fractions).

Fluids that dissolve in another fluid are described as miscible in that fluid.

The temperature at which a substance changes between a liquid state and a gas state is known as its boiling point.

A fractionating column is a piece of apparatus within which a temperature gradient develops.  It is used during fractional distillation.

Distillation: fractional distillation

A single element or compound that is not mixed with any other substance.

The process of killing bacteria and other living microorganisms.

The process of removing dissolved salts from seawater.

The movement of solvent through a semipermeable membrane by applying excess pressure on the solution. This process can remove dissolved solutes from water.

Separating substances

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These lessons will be removed by end of Summer Term 2025.