AQA GCSE Chemistry (Triple) - Paper 1 Exam-Style Flashcards: Topic 4 - Chemical Changes

A set of exam-style flashcards covering the key concepts of chemical changes, including ions, reactions, electrolysis, and the reactivity series.

What ions do all acids contain?

Hydrogen ions, H+ (aq).

What ions do all alkalis contain?

Hydroxide ions, OH- (aq).

Write the general reaction between an acid and a metal.

Acid + Metal → Salt + Hydrogen.

Write the general reaction between an acid and a base.

Acid + Base → Salt + Water.

What type of reaction is acid + base?

Neutralisation.

What gas is produced when acids react with metals?

Hydrogen gas (H2).

Describe a test for hydrogen gas.

A lit splint gives a ‘squeaky pop’ sound.

What equipment is used to prepare a pure, dry, insoluble salt?

Add excess base to acid → filter → heat → crystallise.

Why is excess base added when preparing a salt?

To ensure all acid reacts and no acid remains.

What does filtering remove in the salt preparation?

Unreacted solid (excess base).

What is the reactivity series?

A list of metals in order of how easily they lose electrons (form positive ions).

State the reactivity series.

Potassium, Sodium, Lithium, Calcium, Magnesium, Carbon, Zinc, Iron, Hydrogen, Copper.

What happens when a more reactive metal reacts with a less reactive metal’s compound?

A displacement reaction occurs.

Write the ionic equation for magnesium displacing copper.

Mg + Cu²+ → Mg²+ + Cu.

What is oxidation?

Gain of oxygen or loss of electrons.

What is reduction?

Loss of oxygen or gain of electrons.

In a redox reaction, what happens to the oxidising agent?

It gains electrons (is reduced).

In a redox reaction, what happens to the reducing agent?

It loses electrons (is oxidised).

What is electrolysis?

The decomposition of a compound using electricity.

What type of substances can be electrolysed?

Ionic compounds in the molten or dissolved (aqueous) state.

What happens at the cathode (negative electrode)?

Positive ions (cations) gain electrons — reduction occurs.

What happens at the anode (positive electrode)?

Negative ions (anions) lose electrons — oxidation occurs.

In electrolysis of molten lead bromide (PbBr2), what forms at each electrode?

Cathode: Lead (Pb); Anode: Bromine (Br2).

What two sources of ions are present in aqueous solutions?

From the compound and from water (H+ and OH-).

At the cathode, which ion is discharged?

The least reactive positive ion (usually hydrogen if the metal is more reactive).

At the anode, which ion is usually discharged?

Usually oxygen gas from hydroxide ions (unless halide ions are present).

What is the test for oxygen gas?

Relights a glowing splint.

What are the products of the electrolysis of brine?

Hydrogen gas (cathode), chlorine gas (anode), sodium hydroxide (in solution).

Give one industrial use for each product of brine electrolysis.

Hydrogen: fuel/ammonia; Chlorine: PVC/disinfectants; Sodium hydroxide: soap/paper.