Interpreting chromatograms
Lesson details
Learning outcome
I can analyse chromatograms both qualitatively and quantitatively.
Key learning points
- Chromatograms can identify unknown substances by qualitative visual comparison or quantitatively by Rf value comparison.
- Appropriate equipment should be employed when using chromatograms to identify unknown substances in a mixture.
- An appropriate number of significant figures should be used in calculations.
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.
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).
Teacher tip
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.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.What is an element?
Q2.True or false? All pure substances are elements.
Q3.True or false? If something is not pure, it is a mixture.
Q4.True or false? All mixtures can be separated into their individual components through physical processes.
Q5.What is the purpose of chemical analysis?
Q6.Solubility is a measure of how well a substance can in a solvent.
Assessment exit quiz
6 Questions
Q1.The pattern that forms as a result of chromatography is called a ...
Q2.Match the keyword to its description.
the furthest distance the solvent travels along the stationary phase
where the sample is placed on the stationary phase
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?
Q4.How can chromatograms be used to identify if a sample is a mixture?
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.
Q6.Given a solvent front at 7.0 cm and a substance spot at 2.3 cm on a chromatogram, calculate the Rf value.
To help you plan your 10 combined science lesson on: Interpreting chromatograms, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 10 combined science lesson on: Interpreting chromatograms, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 4 combined science lessons from the Separating substances unit, dive into the full secondary combined science curriculum, or learn more about lesson planning.