Paper chromatography lab
Run paper chromatograms of dyes, inks and amino acids, measure Rf values with a ruler, match an unknown with known samples and see why the start line is in pencil above the solvent.
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Learning goals
- describe methods of separation and purification for the components of mixtures, to include: — paper chromatography
Learning objectives
- describe methods of separation and purification for the components of mixtures, to include: — paper chromatography
- interpret paper chromatograms including comparison with ‘known’ samples and the use of Rf values
- explain the need to use locating agents in the chromatography of colourless compounds (knowledge of specific locating agents is not required)
- interpret paper chromatograms including comparison with ‘known’ samples (the use of Rf values is not required)
Paper chromatography of food colouring X, red dye, blue dye, yellow dye in water, with the start line in pencil and the solvent below the start line. The solvent has not reached the start line yet. The ruler's zero is not on the start line and its cursor reads 4.0 cm.
- Ruler reading at the cursor
- 4.0 cm
- Rf from your readings
- —
Try this
0 of 4 doneRun one chromatogram with an ink start line and one with the solvent above the start line. (not done yet)
Ink dissolves and runs up the paper with the samples; pencil graphite does not. Solvent above the start line dissolves the spots into the beaker instead of carrying them up the paper.
When the run ends, put the ruler beside a lane with its zero on the start line. Record the distances to a spot's centre and to the solvent front. (not done yet)
Rf = distance moved by the spot ÷ distance moved by the solvent front. Both are measured from the start line, so Rf has no unit and lies between 0 and 1.
Find a known sample with a spot at the same Rf as a spot of the unknown in lane 1. (not done yet)
Spots with the same Rf and colour, run in the same solvent on the same paper, are probably the same substance. A match supports an identity; it does not prove it.
Run the amino acids, then spray the paper with the locating agent. (not done yet)
Amino acids are colourless. A locating agent reacts with them to form coloured spots, so their positions can be seen and measured.
Your readings
| # | lane | d / cm | Remove |
|---|---|---|---|
| No readings yet. Set up a measurement, then record it. | |||