New
New
Year 10
Edexcel
Higher

Interpreting chromatograms

I can analyse chromatograms both qualitatively and quantitatively.

New
New
Year 10
Edexcel
Higher

Interpreting chromatograms

I can analyse chromatograms both qualitatively and quantitatively.

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Lesson details

Key learning points

  1. Chromatograms can identify unknown substances by qualitative visual comparison or quantitatively by Rf value comparison.
  2. Appropriate equipment should be employed when using chromatograms to identify unknown substances in a mixture.
  3. An appropriate number of significant figures should be used in calculations.

Common misconception

Pupils can struggle to interpret information that contains several samples on one chromatogram.

Stress a systematic approach to interpreting chromatograms (i.e. use rulers). Live model this (using a visualiser helps enormously).

Keywords

  • Solvent front - The solvent front is the furthest distance the solvent travels along the stationary phase during chromatography.

  • Sample line - The sample line is where the sample undergoing chromatography is placed on the stationary phase.

  • Rf value - 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.

  • Chromatogram - A chromatogram is the resultant pattern on the stationary phase after chromatography has been carried out.

Prepare some chromatograms of a sample in different mobile phases (e.g. water, ethanol, propanone) to stress the effect the choice of mobile phase has on the effectiveness of analysing the resultant chromatograms.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Video

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6 Questions

Q1.
What is an element?
a metal
a compound
Correct answer: a pure substance made of one kind of atom
a mixture
Q2.
True or false? All pure substances are elements.
true
Correct answer: false
Q3.
True or false? If something is not pure, it is a mixture.
Correct answer: true
false
Q4.
True or false? All mixtures can be separated into their individual components through physical processes.
Correct answer: true
false
Q5.
What is the purpose of chemical analysis?
to break down substances
Correct answer: to find out the composition of a substance
to create new elements
to study biological organisms
Q6.
Solubility is a measure of how well a substance can in a solvent.
Correct Answer: dissolve

6 Questions

Q1.
The pattern that forms as a result of chromatography is called a ...
Correct Answer: chromatogram
Q2.
Match the keyword to its description.
Correct Answer:solvent front,the furthest distance the solvent travels along the stationary phase

the furthest distance the solvent travels along the stationary phase

Correct Answer:sample line,where the sample is placed on the stationary phase

where the sample is placed on the stationary phase

Correct Answer:Rf value,a ratio of the distance a component of a sample travels vs the solvent

a ratio of the distance a component of a sample travels vs the solvent

Q3.
Which of the following pieces of apparatus and equipment is not essential for chromatography?
chromatography paper
container (e.g. beaker)
pencil
ruler
Correct answer: a pen
Q4.
How can chromatograms be used to identify if a sample is a mixture?
by the colour of the sample line
Correct answer: by the presence of multiple spots
by the number of peaks
by the Rf value of a spot
Q5.
A vertical analysis of a sample’s chromatogram can visually determine if a sample is pure or a mixture. This is known as analysis.
Correct Answer: qualitative
Q6.
Given a solvent front at 7.0 cm and a substance spot at 2.3 cm on a chromatogram, calculate the Rf value.
Correct Answer: 0.33, 0.329