Purity, formulations and chromatography Chemical analysis Revision…

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Pure substances7 objectives

Define a pure substance in chemistry as a single element or compound not mixed with any other substance.
Explain that a pure element or compound melts and boils at specific temperatures.
Use melting point data to identify a pure substance.
Use boiling point data to identify a pure substance.
Explain that impurities change the melting point and boiling point of a substance.
Interpret melting point or boiling point data to decide whether a substance is pure or impure.
Distinguish the chemistry meaning of pure substance from everyday meanings of purity.

Formulations7 objectives

Define a formulation as a mixture that has been designed as a useful product.
Explain that formulations are made by mixing components in carefully measured quantities.
Describe why the properties of a formulation depend on its components and their amounts.
Identify examples of formulations such as fuels, cleaning agents, paints, medicines, fertilisers and alloys.
Explain that each component in a formulation contributes to the properties of the product.
Interpret information about formulation composition and purpose.
Distinguish a formulation from a pure substance and from an unplanned mixture.

Chromatography12 objectives

Describe chromatography as a method used to separate mixtures and identify substances.
Explain that chromatography involves a stationary phase and a mobile phase.
Explain that separation depends on the distribution of substances between the mobile phase and the stationary phase.
Describe how paper chromatography separates soluble substances such as coloured inks or food colourings.
Interpret a chromatogram to identify whether a sample is pure or a mixture.
Explain that a pure substance produces a single spot on a chromatogram.
Explain that a mixture may produce more than one spot on a chromatogram.
Compare spots from unknown substances with known substances on the same chromatogram.
Calculate Rf values using distance moved by substance divided by distance moved by solvent.
Use Rf values to compare and identify substances.
Explain why Rf values are only useful for comparison under the same conditions.
Investigate how paper chromatography can be used to separate and identify mixtures. (AT 1, 4, 6; WS 2.2, 2.4; MS 1a, 1c)

Key terms

Pure substanceImpurityPure SubstanceMelting Pointpure substancemelting pointBoiling pointMelting point depressionBoiling point elevationBoiling PointEveryday purityformulation

Exam tips

Understanding Pure Substances: Remember that a pure substance is defined as a single element or compound that is not mixed with any other substance. Use this definition to differentiate between pure substances and mixtures in your exam.
Understand Melting and Boiling Points: Memorize the specific melting and boiling points of common pure substances to quickly identify them during the exam.

Common mistakes

Misunderstanding Pure Substances: A pure substance must be a single element or compound with no other substances mixed in.
Misunderstanding Melting and Boiling Points: Remember that a pure element or compound has specific melting and boiling points, while impurities can alter these temperatures.

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