C1 - Paper Chromatography

What is chromatography used for?

To separate substances in a mixture based on their solubilities.

What type of separation method is chromatography?

A physical separation technique (no chemical reaction occurs).

What is the most common type of chromatography in GCSE Chemistry?

Paper chromatography.

What is the name of the special paper used in this method?

Chromatography paper.

What do we use to draw the starting line in chromatography?

Pencil.

Why must we use pencil to draw the starting line?

Because pen ink might dissolve in the solvent and interfere with the results.

What is placed on the pencil line?

Dots of the different colored substances (e.g. from pens or inks).

What is the solvent in chromatography?

A liquid that dissolves substances and moves up the paper.

What is an example of a solvent used in chromatography?

Water or ethanol, depending on the substances.

What do we call the paper in chromatography?

The stationary phase.

Why is the paper called the stationary phase?

Because it does not move during the experiment.

What do we call the solvent in chromatography?

The mobile phase.

Why is the solvent called the mobile phase?

Because it moves up the paper carrying the substances with it.

What happens as the solvent moves up the paper?

It dissolves the substances and carries them different distances.

What does the distance a substance travels depend on?

Its solubility in the solvent.

What happens to a substance that is more soluble in the solvent?

It travels further up the paper.

What happens to a substance that is less soluble in the solvent?

It travels a shorter distance up the paper.

What does it mean if a substance produces only one spot on the paper?

It is a pure substance.

What does it mean if a substance separates into multiple spots?

It is a mixture of different substances.

Does a pure substance always produce a single spot in every solvent?

Yes, a pure compound gives a single spot in all solvents.

Can the position of the spot change in different solvents?

Yes, but a pure substance will still produce only one spot.

What does it mean if a mixture separates into different spots in different solvents?

It contains substances with different solubilities.

Why do substances travel different distances in chromatography?

Because they have different attractions to the mobile phase (solvent).

What is the mobile phase in paper chromatography?

The solvent that moves.

What is the stationary phase in paper chromatography?

The paper that stays still.

Why must the solvent level stay below the pencil line?

So the sample doesn't dissolve directly into the solvent.

What happens if the solvent touches the ink spots at the start?

The inks may dissolve directly into the solvent and not separate properly.

Why is chromatography useful in chemistry?

It helps identify substances and test for purity.

What is the result of a chromatography experiment called?

A chromatogram.

What does a chromatogram show?

The separated spots of substances after chromatography.

What should you compare to identify unknown substances?

The position and number of spots with known samples.

What will be discussed in chromatography in later topics?

How to calculate the Rf value to help identify substances.

What is the formula for Rf value?

Rf = distance moved by substance ÷ distance moved by solvent.

What is a typical exam question about drawing the start line?

Why must you use pencil instead of pen?

How do you know if a substance is pure from a chromatogram?

It shows a single spot.

How do you know if a substance is a mixture from a chromatogram?

It separates into more than one spot.

What does a spot higher up the paper mean?

That substance is more soluble in the solvent.

Can chromatography be used on colorless substances?

Yes, but special locating agents (e.g. UV light) may be needed.