Starter quiz
- What is an element?
- a metal
- a compound
- a pure substance made of one kind of atom ✓
- a mixture
-
- True or false? All pure substances are elements.
- True
- False ✓
- True or false? If something is not pure, it is a mixture.
- True ✓
- False
- True or false? All mixtures can be separated into their individual components through physical processes.
- True ✓
- False
- What is the purpose of chemical analysis?
- to break down substances
- to find out the composition of a substance ✓
- to create new elements
- to study biological organisms
-
- Solubility is a measure of how well a substance can ______ in a solvent.
- 'dissolve' ✓
Exit quiz
- The pattern that forms as a result of chromatography is called a ...
- 'chromatogram' ✓
- Match the keyword to its description.
- solvent front⇔the furthest distance the solvent travels along the stationary phase ✓
- sample line⇔where the sample is placed on the stationary phase ✓
- Rf value⇔a ratio of the distance a component of a sample travels vs the solvent ✓
- Which of the following pieces of apparatus and equipment is not essential for chromatography?
- chromatography paper
- container (e.g. beaker)
- pencil
- ruler
- a pen ✓
-
- How can chromatograms be used to identify if a sample is a mixture?
- by the colour of the sample line
- by the presence of multiple spots ✓
- by the number of peaks
- by the Rf value of a spot
-
- A vertical analysis of a sample’s chromatogram can visually determine if a sample is pure or a mixture. This is known as ______ analysis.
- 'qualitative' ✓
- Given a solvent front at 7.0 cm and a substance spot at 2.3 cm on a chromatogram, calculate the Rf value.
- '0.33' ✓
Worksheet
Presentation
Video
Lesson Details
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.
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.