Topic 8: Chemical Analysis

What is a pure substance (chemically)?

A single element or compound, not mixed with any other substance.

How can you tell if a substance is pure?

It melts and boils at a specific temperature.

What is a formulation?

A useful mixture made with exact amounts of each component.

Give examples of formulations.

Paints, fuels, medicines, alloys, fertilisers, and foods.

What is chromatography used for?

To separate mixtures and identify substances.

What are the phases in chromatography?

Stationary phase (paper) and mobile phase (solvent).

What is the Rf value and how is it calculated?

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

How do you know if a substance is pure using chromatography?

A pure compound produces one spot in all solvents.

What is the test for hydrogen?

Lit splint at the test tube mouth → squeaky pop.

What is the test for oxygen?

Glowing splint relights in the test tube.

What is the test for carbon dioxide?

Bubble it through limewater → turns milky/cloudy.

What is the test for chlorine?

Damp litmus paper is bleached white.

What colour flame does lithium produce?

Crimson

What colour flame does sodium produce?

Yellow

What colour flame does potassium produce?

Lilac

What colour flame does calcium produce?

Orange-red

What colour flame does copper produce?

Green

What precipitate do aluminium, calcium, and magnesium form with NaOH?

White – only aluminium dissolves in excess NaOH.

What colour precipitate does copper(II) form with NaOH?

Blue

What colour precipitate does iron(II) form with NaOH?

Green

What colour precipitate does iron(III) form with NaOH?

Brown

How do you test for carbonates?

Add acid → CO₂ produced → bubble through limewater → turns cloudy.

How do you test for halides?

Add dilute nitric acid, then silver nitrate:

• Chloride = white

• Bromide = cream

• Iodide = yellow

How do you test for sulfates?

Add HCl and then barium chloride → white precipitate if sulfate is present.

What is flame emission spectroscopy?

An instrumental method that identifies metal ions and measures concentration from line spectra.

Why are instrumental methods used?

They are accurate, sensitive, and fast.