1.4 Chemical changes

What is formed when metals react with oxygen?

Metal oxides

What is oxidation (in terms of oxygen)?

Gain of oxygen

What is reduction (in terms of oxygen)?

Loss of oxygen

What is the reactivity series?

A list of metals ordered by how reactive they are

What does reactivity depend on?

Tendency to lose electrons and form positive ions

What happens when metals react?

They form positive ions

What is a displacement reaction?

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

Where are very unreactive metals like gold found?

As native (pure) metals in the Earth

How are less reactive metals than carbon extracted?

Reduction with carbon

What does reduction involve?

Loss of oxygen

What does OIL RIG stand for?

Oxidation Is Loss, Reduction Is Gain (of electrons)

What is oxidation (in terms of electrons)?

Loss of electrons

What is reduction (in terms of electrons)?

Gain of electrons

Write the oxidation half equation for sodium.

Na → Na⁺ + e⁻

Write the reduction half equation for sodium ion.

Na⁺ + e⁻ → Na

How do you identify oxidation in a reaction?

Loss of electrons

How do you identify reduction in a reaction?

Gain of electrons

In 2Na + 2HCl → 2NaCl + H₂, what happens to sodium?

It is oxidised (loses electrons)

What happens to hydrogen?

It is reduced (gains electrons)

What is a redox reaction?

A reaction where oxidation and reduction occur together

What is the general reaction of acids with metals?

Acid + metal → salt + hydrogen

In Mg + 2HCl → MgCl₂ + H₂, what happens to magnesium?

It is oxidised (loses electrons)

What happens to hydrogen ions?

They are reduced (gain electrons)

What is neutralisation?

Reaction of an acid with a base or alkali to form salt and water

What is the general equation for neutralisation?

Acid + base → salt + water

What is the equation for acids with carbonates?

Acid + carbonate → salt + water + carbon dioxide

What determines the type of salt formed?

The acid used

What salt is formed with hydrochloric acid?

Chlorides

What salt is formed with nitric acid?

Nitrates

What salt is formed with sulfuric acid?

Sulfates

What must charges in a salt equal?

Overall zero

How are soluble salts made?

React acid with excess insoluble solid, filter, then crystallise

What is crystallisation?

Evaporating solution to form crystals

What ions do acids produce in solution?

H⁺ ions

What ions do alkalis produce?

OH⁻ ions

What is the pH scale?

A measure of acidity/alkalinity from 0 to 14

What is neutral pH?

7

What is acidic pH?

Below 7

What is alkaline pH?

Above 7

What is the ionic equation for neutralisation?

H⁺ + OH⁻ → H₂O

What is a strong acid?

Completely ionised in solution

What is a weak acid?

Partially ionised in solution

Give examples of strong acids.

HCl, HNO₃, H₂SO₄

Give examples of weak acids.

Ethanoic, citric, carbonic

What happens when pH decreases by 1?

H⁺ concentration increases by 10×

What is the difference between strong and concentrated?

Strength = ionisation, concentration = amount per volume

What is electrolysis?

Breaking down an ionic compound using electricity

What is the electrolyte?

The substance being broken down

Where do positive ions go in electrolysis?

Cathode (negative electrode)

Where do negative ions go?

Anode (positive electrode)

What happens at the cathode?

Reduction (gain of electrons)

What happens at the anode?

Oxidation (loss of electrons)

What happens in electrolysis of molten compounds?

Metal forms at cathode, non-metal at anode

Why are reactive metals extracted by electrolysis?

Too reactive to be reduced by carbon

How is aluminium extracted?

Electrolysis of molten aluminium oxide

Why is cryolite used?

To lower melting point and reduce energy cost

Why must carbon anodes be replaced?

They react with oxygen to form CO₂

What happens at the cathode in aqueous electrolysis?

Hydrogen is produced unless metal is less reactive than hydrogen

What happens at the anode in aqueous electrolysis?

Halogen forms if present, otherwise oxygen

Why does water affect electrolysis of solutions?

It produces H⁺ and OH⁻ ions

What is a half equation?

Equation showing electron transfer at one electrode

Write a reduction half equation.

X⁺ + e⁻ → X

Write an oxidation half equation.

X⁻ → X + e⁻