Chemical analysis fulls set

What is a pure substance in chemistry?

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

How can you tell if a substance is pure?

It has a specific, fixed melting and boiling point.

What is a formulation?

A mixture that has been designed as a useful product.

Give an example of a formulation.

Paint, medicine, cleaning products, fuels.

What does chromatography separate?

Components of a mixture.

What is the mobile phase in chromatography?

The solvent that moves through the paper.

What is the stationary phase in chromatography?

The paper that does not move.

How does chromatography work?

Different substances are carried different distances depending on their solubility.

What is an Rf value?

The ratio of the distance moved by the substance to the distance moved by the solvent.

What is the formula for calculating Rf value?

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

What does an Rf value tell us?

How far a substance travels compared to the solvent – useful for identification.

What does it mean if a substance has only one spot in chromatography?

It is a pure substance.

What are the four main gases tested in chemical analysis?

Hydrogen, oxygen, carbon dioxide, and chlorine.

How do you test for hydrogen?

Lit splint gives a squeaky pop.

How do you test for oxygen?

A glowing splint relights.

How do you test for carbon dioxide?

Turns limewater cloudy.

How do you test for chlorine?

Bleaches damp litmus paper white.

What are flame tests used for?

Identifying metal ions.

What colour flame does lithium produce?

Crimson red.

What colour flame does sodium produce?

Yellow/orange.

What colour flame does potassium produce?

Lilac.

What colour flame does calcium produce?

Brick red.

What colour flame does copper produce?

Green.

What is a limitation of flame tests?

Mixtures can mask colours.

What is the test for metal hydroxides?

Add sodium hydroxide to form coloured precipitates.

What colour precipitate does aluminium form with NaOH?

White, then redissolves in excess NaOH.

What colour precipitate does calcium form with NaOH?

White.

What colour precipitate does magnesium form with NaOH?

White.

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 carbonate ions?

Add dilute acid – if it fizzes, bubble gas through limewater.

What is the positive result for a carbonate ion test?

Limewater turns cloudy due to CO₂.

How do you test for halide ions?

Add dilute nitric acid, then silver nitrate solution.

What precipitate does chloride form in halide test?

White.

What precipitate does bromide form in halide test?

Cream.

What precipitate does iodide form in halide test?

Yellow.

How do you test for sulfate ions?

Add dilute HCl and barium chloride solution.

What is the positive result for sulfate ions?

A white precipitate of barium sulfate forms.

Why is hydrochloric acid added before the sulfate test?

To remove carbonate ions which would also form a precipitate.

Why is nitric acid used before the halide test?

To remove carbonate ions which could interfere with results.

What is instrumental analysis?

Using machines to analyse substances quickly and accurately.

Give one advantage of instrumental methods.

Faster, more accurate, and sensitive than chemical tests.