Topic 4: Chemical Changes

What is the word equation for a metal reacting with oxygen?

Metal + Oxygen → Metal Oxide (oxidation reaction)

What is the reactivity series used for?

To rank metals by how easily they form positive ions (i.e., their reactivity).

What happens in a displacement reaction?

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

How are metals less reactive than carbon extracted?

By reduction with carbon (removal of oxygen).

What does OIL RIG stand for in terms of electrons?

Oxidation Is Loss, Reduction Is Gain (of electrons).

What is the general word equation for acid and metal reactions?

Acid + Metal → Salt + Hydrogen

What are redox reactions?

Reactions where one substance is oxidised and another is reduced.

What is the ionic equation for magnesium reacting with HCl?

Mg → Mg²⁺ + 2e⁻ (oxidation); 2H⁺ + 2e⁻ → H₂ (reduction)

What is the general equation for neutralisation?

Acid + Base/Alkali → Salt + Water

What does acid + carbonate produce?

Salt + Water + Carbon dioxide

How do you make a soluble salt from an insoluble base?

Add excess base to acid, filter excess, then crystallise the salt.

What ions do acids and alkalis produce in water?

Acids: H⁺ ions; Alkalis: OH⁻ ions

What is the ionic equation for any neutralisation reaction?

H⁺ + OH⁻ → H₂O

What does a titration do?

Measures the volume of acid needed to exactly neutralise an alkali.

What is the difference between strong and weak acids?

Strong acids fully ionise in water; weak acids only partially ionise.

How does pH relate to H⁺ concentration?

A decrease of 1 pH unit = 10× increase in H⁺ concentration.

What is electrolysis?

Splitting of an ionic compound using electricity when ions are free to move.

What happens at the cathode during electrolysis?

Positive ions (cations) are reduced (gain electrons).

What happens at the anode during electrolysis?

Negative ions (anions) are oxidised (lose electrons).

Why is cryolite used in aluminium extraction?

It lowers the melting point of aluminium oxide, saving energy.

Why must carbon electrodes in aluminium extraction be replaced?

They react with oxygen to form CO₂ and burn away.

In aqueous electrolysis, when is hydrogen produced at the cathode?

When the metal is more reactive than hydrogen.

What is produced at the anode if no halide ions are present?

Oxygen (from OH⁻ ions).

Write the half-equation for sodium ion reduction.

Na⁺ + e⁻ → Na

Write the half-equation for bromide ion oxidation.

2Br⁻ → Br₂ + 2e⁻