Lesson Plan: C2.3.03

Hamble Lesson Observation Plan
Learning About
How can we use paper chromatography to identify an unknown mixture?
Keywords:
  • Instrumental method: The use of instruments to separate, identify, and quantify matter. (1)
  • Rf Value: In chromatography is the distance travelled by a given component divided by the distance travelled by the solvent front. (1)
  • Stationary phase: The phase of a chromatography system on which the materials to be separated are selectively adsorbed. (1)
  • Mobile phase: flows through the stationary phase and carries the components of the mixture with it. (1)
  • Chromatography: A technique for the separation of a mixture by passing it in solution or suspension through a medium in which the components move at different rates. (1)
Memory Anchor:
Method Precise Learning Objective Linked Question / Activity
(Designed for maximum working out)		 Stepping Stones Pitstop Check
(Thinking Map)
Chromatography can be used to separate mixtures and can give information to help identify substances. What can Chromatography be used to separate?
Chromatography involves a stationary phase and a mobile phase. What are the names of the two phases involved in chromatography?
Separation depends on the distribution of substances between the phases What does seperation depend on?

Watch video of cars racing down runway (attached on ppt on shared drive). Thinking point - Why did the cars cross the line at different times?
The ratio of the distance moved by a compound (centre of spot from origin) to the distance moved by the solvent can be expressed as its R value How should the Rf value be expressed?
RT = distance moved by substance / distance moved by solvent How is the Rf value calculated?
Different compounds have different R values in different solvents, How do the Rf values of compounds change in different solvents?

Students use mock chromatograms to calculate Rf values and identify unknown substance. Spice it up as a ransom note.
Rf values can be used to help identify the compounds. How can compounds be identified?
The compounds in a mixture may separate into different spots depending on the solvent but a pure compound will produce a single spot in all solvents. How many spots are produced by a pure compound compared to a compound in a mixture?
Students should be able to explain how paper chromatography separates mixtures How can paper chromatography be used to separate mixtures?

Research where chromatography is used in forensics - Inks, colourings, dyes, drugs etc
Students should be able to suggest how chromatographic methods can be used for distinguishing pure substances from impure substances How can chromatographic methods can be used for distinguishing pure substances from impure substances?
Students should be able to interpret chromatograms and determine R values from chromatograms How can chromatograms be used to determine R values?
provide answers to an appropriate number of significant figures. (MS)

Elements and compounds can be detected and identified using instrumental methods. Instrumental methods are accurate, sensitive and rapid. How can elements and compounds be detected?

Students should be able to state advantages of instrumental methods compared with the chemical tests in this specification. What are the advantages of instrumental methods compared with the chemical tests?
Links To the Big Ideas
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