2.3 Chemical analysis

What is a pure substance?

A single element or compound not mixed with anything else

What is a key property of pure substances?

They have fixed melting and boiling points

How can melting point be used?

To distinguish pure substances from mixtures

What is the everyday meaning of pure?

A substance with nothing added

What is a formulation?

A mixture designed as a useful product

Why are formulations made carefully?

To ensure specific properties

Give examples of formulations

Fuels Cleaning agents Paints Medicines Alloys Fertilisers Foods

What is chromatography used for?

Separating mixtures and identifying substances

What are the two phases in chromatography?

Stationary phase and mobile phase

What does separation depend on?

Distribution between the two phases

What is the Rf value?

Distance moved by substance divided by distance moved by solvent

What do different Rf values indicate?

Different substances

How many spots does a pure substance produce?

One spot

How many spots does a mixture produce?

Multiple spots

What is paper chromatography?

Separating substances by how far they travel on paper

What determines how far a substance travels?

Its solubility in the solvent

What is a pigment?

A coloured substance

How do you test for hydrogen?

Use a burning splint

What is the result for hydrogen?

Squeaky pop sound

How do you test for oxygen?

Use a glowing splint

What is the result for oxygen?

Splint relights

How do you test for carbon dioxide?

Bubble through limewater

What is the result for carbon dioxide?

Turns milky cloudy

How do you test for chlorine?

Use damp litmus paper

What is the result for chlorine?

Bleaches paper white