Chromatography practical activity
Separation techniques
It is important in this core practical to use a range of equipment and methods to separate chemical mixtures. This includes the safe use and careful handling of substances.
This outlines one way to carry out the practical. Eye protection must be worn.
Aims
To investigate the composition of inks using paper chromatographyChromatography is used to separate different substances dissolved in a liquid..
Method
- draw a pencil line across the chromatography paper, 1-2 cm from the bottom
- use a pipette or capillary tubeGlass tubing which is very narrow inside. to add small spots of each ink to the line on the paper
- place the paper into a container with a suitable solvent in the bottom
- allow the solvent to move through the paper, but remove the chromatogramThe results of separating mixtures by chromatography. before the solvent reaches the top
- mark the level that the solvent reached using a pencil so that you can measure the distance travelled by the solvent when it dries
- allow the chromatogram to dry, then measure the distance travelled by each spot and by the solvent
Results
1. Record your results in a suitable table. For example:
| Ink | Spot colour | Distance travelled by spot (mm) |
| Ink | |
|---|---|
| Spot colour | |
| Distance travelled by spot (mm) |
Analysis
2. Calculate the Rf value of each spot:
Rf = \( \frac{distance \ travelled \ by \ substance}{distance\ travelled\ by\ solvent }\)
3. Compare the Rf values and colours of each spot in the inks. Describe their similarities and differences.
Evaluation
Question
Explain why the distances travelled by each spot were measured in millimetres (mm), rather than in centimetres (cm).
Measurements in mm are more precise than those in cm. They will give more precise Rf values.
Hazards, risks and precautions
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 use a fume cupboard |
| Hazard | Harmful solvent |
|---|---|
| Possible harm | Skin irritation |
| Possible precaution | Avoid skin contact, eg wear gloves |
| Hazard | Harmful solvent |
|---|---|
| Possible harm | Breathing difficulties |
| Possible precaution | Ensure adequate ventilation or use a fume cupboard |