Skip to notes
wise otter.Chemistry
Contents
Experimental Chemistry

Topic 5 of 6

Read the evidence in a chromatogram

Compare spots under the same conditions.

O-Level 5086 / 5088 (2026) / SEC G3 K326 / K328 (2027)

Read the evidence in a chromatogram

Compare spots under the same conditions.

Place small sample spots on a pencil baseline above the solvent level. Ink would dissolve and add unwanted spots. As solvent rises through the paper, substances repeatedly distribute between the solvent and paper; different substances move different distances. Keep the vessel covered and mark the solvent front before it evaporates.

Compare an unknown with standards

Unknown U has two spots at the same heights as one spot in A and one in B.

A and B were run alongside U using the same paper and solvent.

Several spots indicate a mixture of separated components. A single spot suggests purity under these conditions, but two substances might move together. A spot matching a known sample supports identification; comparison is meaningful only with the same solvent and conditions.

Check your understandingU has two spots matching A and B. Can you conclude that U contains only A and B with certainty?Think it through, then reveal the answer
The evidence supports A and B being present. Additional substances may coincide with those spots or be invisible under these conditions, so the conclusion is not absolute.