Core practical - investigating the composition of inks
There are a number of ways that you could investigate the composition of inks in Chemistry. This is an outline of the required steps to undertake one of these methods.
Aims
To investigate the composition of inks using simple distillationSeparation method used to separate a solvent from a solution. and chromatographyChromatography is used to separate different substances dissolved in a liquid..
Simple distillation
Method
- Add a small volume of ink to a flask. Connect the flask to the fractionating column and secure it with a stand, boss and clamp.
- Attach a condenser to the top of the fractionating column, connect it to a cold water tap and sink, and secure it over a beaker.
- Heat the flask using a Bunsen burner, reducing the flame as necessary to achieve gentle simmering.
- Collect a small sample of the distilled solventThe liquid in which the solute dissolves to form a solution., then turn the Bunsen burner off.
Results
- describe the appearance of the distilled solvent
- if your apparatus included a thermometer at the top of the column, record the maximum temperature reached as the solvent was collected
Analysis
- Explain any difference in the appearance of the solvent and ink.
- If you measured the maximum temperature, compare this to the boiling points of possible solvents. These could include water, ethanol and propanol.
Evaluation
Discuss whether or not you are able to identify the solvent from the ink.
Paper chromatography
Method
- draw a pencil line across the chromatography paper, 1-2 cm from the bottom
- use a pipette or capillary tube 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 it reaches the top
- allow the chromatogram to dry, then measure the distance travelled by each spot and by the solvent
Results
- 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) |
| Ink | |
|---|---|
| Spot colour | |
| Distance travelled by spot (mm) |
Analysis
- Calculate the Rf value of each spot.
- 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 mm, rather than in cm.
Measurements in millimetres are more precise than those in centimetres. They will give more precise Rf values.
Hazards, risks and precautions
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 | Harm | Precaution |
| Hot apparatus | Skin burns | Allow apparatus to cool before touching it |
| Bunsen burner flame | Skin burns | Keep hair and clothes tucked in |
| Bunsen burner flame | Fire | Do not bring flammable solvents near to the flame |
| Harmful solvent | Skin irritation | Avoid skin contact, eg wear gloves |
| Harmful solvent | Breathing difficulties | Ensure adequate ventilation or use a fume cupboard |
| Hazard | Hot apparatus |
|---|---|
| Harm | Skin burns |
| Precaution | Allow apparatus to cool before touching it |
| Hazard | Bunsen burner flame |
|---|---|
| Harm | Skin burns |
| Precaution | Keep hair and clothes tucked in |
| Hazard | Bunsen burner flame |
|---|---|
| Harm | Fire |
| Precaution | Do not bring flammable solvents near to the flame |
| Hazard | Harmful solvent |
|---|---|
| Harm | Skin irritation |
| Precaution | Avoid skin contact, eg wear gloves |
| Hazard | Harmful solvent |
|---|---|
| Harm | Breathing difficulties |
| Precaution | Ensure adequate ventilation or use a fume cupboard |