To investigate how paper chromatography can be used to separate and tell the difference between coloured substances.
Record your results in a suitable table. For example:
|Ink||Spot colour||Distance travelled by spot (mm)|
1. Calculate the Rf value of each spot:
2. Compare the Rf values and colours of each spot in the inks. Describe their similarities and differences.
Explain why the distances travelled by each spot were measured in mm, rather than in cm.
Measurements in millimetres are more precise than those in centimetres. They will give more precise Rf values.
It is important in this practical activity to use appropriate apparatus and methods. This includes the safe use and careful handling of substances. Eye protection must be worn.
Evaluate the hazards and the precautions needed to reduce the risk of harm. For example:
|Hazard||Possible harm||Possible precaution|
|Harmful solvent||Skin irritation||Avoid skin contact, eg wear gloves|
|Harmful solvent||Breathing difficulties||Ensure adequate ventilation or carry out the chromatography in a fume cupboard|
Mixtures of these pigments from chloroplasts can be separated using paper chromatography.
The pigments can be extracted from leaves by grinding the leaves in organic solvents with a pinch of sand to break up the plant cells.
The pigments can be separated using a mixture of organic solvents.