Student Book Links

Student book links / Specification links / Link to AS specification / Suggested time allowed (includes contact and non-contact time):
·  1.3.1–4 / ·  4.3.1 (a)–(h) / ·  2.2.3 Modern analytical techniques / Four to five hours
Suggested teaching order
1.  Explain the terms: chromatography, mobile phase and stationary phase.
2.  Describe separation by adsorption and by relative solubility.
3.  Describe thin-layer chromatography (TLC).
4.  Describe gas chromatography (GC).
5.  Explain Rf values and retention time.
6.  Describe the extra usefulness of GC–MS and the uses to which it can be put.
Weekly learning outcomes
Students should be able to:
·  Describe chromatography as an analytical technique that separates components in a mixture between a mobile phase and a stationary phase.
·  State that the mobile phase may be a liquid or a gas.
·  State that the stationary phase may be a solid, or either a liquid or solid on a solid support.
·  State that a solid stationary phase separates by adsorption.
·  State that a liquid stationary phase separates by relative solubility.
·  State that the mobile phase in TLC is a liquid and the stationary phase is a solid on a solid support and that the solid stationary phase in TLC separates by adsorption.
·  Explain the term Rf value and interpret chromatograms in terms of Rf values.
·  Explain the term retention time and interpret gas chromatograms in terms of retention times and the approximate proportions of the components of a mixture.
·  Explain that analysis by gas chromatography has limitations.
·  Explain that mass spectrometry can be combined with chromatography in GC–MS to provide a far more powerful analytical tool than from gas chromatography alone.
·  Explain that the mass spectra generated can be analysed or compared with spectral databases for positive identification of a component.
·  State the use of GC-MS in analysis – e.g. in forensics, environmental analysis, airport security and space probes.
Key words / How Science Works
Thin-layer chromatography (TLC) Gas chromatography (GC) Rf value
Mobile phase Stationary phase Mass spectra
Adsorption Retardation factor (Rf) Mass spectrometry
Retention time GC–MS / ·  HSW 3 & 7c Use of GC–MS in modern analysis and the use of such evidence in court
Learning styles (S = Starter activities, M = Main activities, P = Plenary activities) / ICT activities
Kinaesthetic
Activity S2
Activities M1–2
Activities P1–2 / Interpersonal
Activities S2–3
Activities M1–2
Activity P1 / Auditory
Activity S3
Activity M3
Activities P1–3 / Visual
Activity S2
Activities M1–3
Activities P1&3 / ·  Research the uses of GC–MS.
·  See also first Homework suggestion below.
·  Produce a PowerPoint presentation showing the separation of one colour into three spots.
Suggested starter activities / Equipment / Teacher notes
1. Revise chromatography – give each student one to three Post-its®, they then must write a fact about chromatography. / Post-its® / Students score points for correct statements, with bonuses for those not mentioned by other students.
2. Quick analysis of simple chromatograms – e.g. testing the blue colour in sweets. / Simple chromatograms on data projector / This is a revision of permitted additives, etc. studied at GCSE.
3. Brainstorm on possible uses of chromatography and
GC–MS. / This may touch on the uses covered in the specification and lead onto activity P3 below.
Suggested main activities / Equipment / Teacher notes
1. Practical activity 11: Thin layer and paper chromatography / See technician worksheet. / See teacher worksheet.
2. Play Whodunnit? / Four different black (or any other four of the same colour) water-based felt tip pens, filter papers with a black dot in the middle from one of the pens / Carry out simple water drip chromatography on the four pens and the unknown.
3. PowerPoint presentation on chromatography / Data projector / See third ICT activity above – probably best to get students to work in groups.
Suggested plenary activities / Equipment / Teacher notes
1. Play Explain the key word. / Key words from this weekly plan written on some cards / Students take turns at drawing a card and then try to explain the key word on the card – extend by withdrawing the easier words and adding new, more difficult ones.
2. Deliver a talk for one minute on GC–MS (see first ICT activity above).
3. Give presentations on the uses of GC–MS. / See the first Homework suggestion below – guide students to cover all the uses in the last learning outcome above.
Homework suggestions
·  Research one different use of chromatography or GC–MS and deliver a one-minute talk or PowerPoint presentation.
·  Practise some exam questions on Methods of analysis and detection from the OCR specification for AS – however, ensure that the questions fit A2.
Cross-curriculum links
·  PHSE – Drugs and drug testing
·  Biology – separation of amino acids by two-way paper chromatography
Stretch and Challenge
·  Research other chromatographic techniques and their historical development.
·  Read an online article about explosives detection in airports.
·  Find out about the separation of amino acids by chromatography.
·  What is electrophoresis? How does it separate the components of a mixture? (This can be linked with amino acids.)
·  Analysis of GC–MS data, e.g. analysis of a reaction mixture with several products
Potential misconceptions
·  Students sometimes believe that any analytical technique will yield a unique compound identification – it often gives clues or narrows down choices but does not elucidate every structure purely by itself.
·  Schools and colleges can often carry out only very simple chromatographic techniques, making this a very theoretical concept – arranging a visit to a local institution that uses chromatographic techniques can make it more meaningful.
Notes