4. Chemical Changes

What does the reactivity series show?

It shows how easily metals lose electrons to form positive ions.

What is oxidation in terms of oxygen?

Gain of oxygen.

What is reduction in terms of oxygen?

Loss of oxygen.

What is oxidation in terms of electrons?

Loss of electrons.

What is reduction in terms of electrons?

Gain of electrons.

What is a displacement reaction?

A more reactive metal displaces a less reactive metal from a compound.

What element can be used to extract metals less reactive than it?

Carbon.

Why can carbon extract iron from iron oxide?

Because carbon is more reactive than iron.

What is the ionic equation for zinc displacing copper?

Zn + Cu²⁺ → Zn²⁺ + Cu

What is the half equation for oxidation of zinc?

Zn → Zn²⁺ + 2e⁻

What is the half equation for reduction of copper ions?

Cu²⁺ + 2e⁻ → Cu

What is the general equation for metal and acid?

Metal + acid → salt + hydrogen

What is the general equation for acid and base?

Acid + base → salt + water

What is the general equation for acid and carbonate?

Acid + carbonate → salt + water + carbon dioxide

What determines the salt formed in a neutralisation reaction?

The acid and the metal/base/carbonate used.

What does hydrochloric acid produce?

Chloride salts.

What does sulfuric acid produce?

Sulfate salts.

What does nitric acid produce?

Nitrate salts.

What is the ionic equation for neutralisation?

H⁺ + OH⁻ → H₂O

What is the pH scale?

A scale from 0 to 14 indicating how acidic or alkaline a solution is.

What does a strong acid do in water?

Fully ionises in aqueous solution.

What does a weak acid do in water?

Partially ionises in aqueous solution.

How much does the H⁺ concentration increase when pH decreases by 1?

Increases by a factor of 10.

What is the difference between strong and concentrated acids?

Strong refers to degree of ionisation, concentrated refers to amount of acid per volume of solution.

What is electrolysis?

Breaking down of a compound using electricity.

What are electrodes?

Conducting rods through which current enters or leaves during electrolysis.

What is formed at the cathode?

Positive ions are reduced (gain electrons).

What is formed at the anode?

Negative ions are oxidised (lose electrons).

What is the half equation for hydrogen gas at the cathode?

2H⁺ + 2e⁻ → H₂

What is the half equation for oxygen gas at the anode?

4OH⁻ → O₂ + 2H₂O + 4e⁻

When is hydrogen formed at the cathode in aqueous solution?

When the metal is more reactive than hydrogen.

When is a metal formed at the cathode in aqueous solution?

When the metal is less reactive than hydrogen.

When is a halogen formed at the anode in aqueous solution?

If halide ions (Cl⁻, Br⁻, I⁻) are present.

When is oxygen formed at the anode in aqueous solution?

If no halide ions are present.

Why is cryolite used in aluminium extraction?

It lowers the melting point of aluminium oxide.

Why do carbon anodes in aluminium electrolysis need replacing?

They react with oxygen to form carbon dioxide.