Separation Methods

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infoWhy this? Mixtures can be separated because their components retain distinct physical properties, such as particle size, solubility, and boiling point. Learning to select and carry out filtration, crystallisation, distillation, and chromatography develops practical problem-solving and an understanding of purity, solutions, and conservation of mass.

scheduleWhy now? The unit directly applies the Year 7 particle model and knowledge of changes of state to dissolving and physical separation. It also establishes the distinction between pure substances and mixtures needed for later work on elements, compounds, chemical reactions, and atomic structure.

A pure substance contains only one type of particle and has a fixed melting and boiling point.
A mixture contains two or more different substances (elements or compounds) not chemically joined together, and does not have a fixed melting or boiling point.
The particle model can be used to represent pure substances (all particles identical) and mixtures (different types of particles present).
Melting point data can be used to identify pure substances (sharp melting point) and mixtures (melting over a range of temperatures).
A solute is a substance that dissolves in a solvent.
A solvent is a substance that dissolves a solute to form a solution.
A solution is a mixture formed when a solute dissolves in a solvent.
The total mass of a solution equals the sum of the masses of the solute and solvent. Mass is conserved when a solution forms.
When a substance dissolves, its particles become evenly distributed among the particles of the solvent.
A saturated solution is one in which no more solute can dissolve at a given temperature.
Solubility is the maximum amount of solute that can dissolve in a solvent at a specific temperature.
As temperature increases, the solubility of most solids in water increases.
Mixtures can be separated by physical methods such as filtration, evaporation, distillation, and chromatography.
Filtration separates insoluble solids from liquids.
Evaporation separates a soluble solid from a solution by removing the liquid as vapour.
Simple distillation can recover a solvent from a solution or separate liquids with sufficiently different boiling points.
Chromatography separates soluble substances based on their movement through a medium.
The arrangement and movement of particles differ in solids (closely packed, vibrate), liquids (close, move past each other), and gases (far apart, move freely).
A control variable is a factor kept constant in an experiment.
An independent variable is the factor that is changed in an experiment.
A dependent variable is the factor that is measured in an experiment.
A pure substance produces a single spot on a chromatogram; a mixture produces two or more spots.

rocket_launchYou must be able to

Represent pure substances and mixtures using the particle model in diagrams.
Use melting point data to identify whether a substance is pure or a mixture.
Describe, using the particle model, what happens when a substance dissolves in a solvent.
Plan and describe a practical to investigate the effect of temperature on solubility, including identifying variables, collecting data, plotting a graph, and drawing a conclusion.
Plot a solubility curve (graph of solubility against temperature) and interpret the relationship.
Describe and select appropriate methods to separate mixtures, including filtration, evaporation, distillation, and chromatography.
Describe and carry out the technique to separate sand and peas using sieving or picking apart based on size.
Explain, using the properties of materials, why a magnet cannot be used to separate aluminium and sand (aluminium is not magnetic).
Describe and perform filtration to separate an insoluble solid from a liquid.
Describe and perform evaporation to separate a soluble solid from a solution.
Explain, using the particle model, how evaporation separates a solid from a solution.
Separate a mixture of a soluble and an insoluble solid by adding a suitable solvent to dissolve the soluble solid, filtering off the insoluble residue, partially evaporating the filtrate, cooling it to crystallise the solute, and then filtering and drying the crystals.
Plan a method to separate pure copper sulphate from a mixture, for example by dissolving, filtering, evaporating, and crystallising.
Explain the changes in state and energy during separation techniques such as evaporation and distillation.
Describe and perform simple distillation to recover a solvent from a solution or separate liquids with sufficiently different boiling points.
Explain, using the particle model, how simple distillation recovers a solvent from a solution or separates liquids with sufficiently different boiling points.
Describe and perform chromatography to separate soluble substances.
Interpret a chromatogram to identify pure substances and mixtures.

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