Unit 5: Reactivity

GRADE 8 – Unit 5: Reactivity — HIA International - Grade 8 Revision Notes & Topical Questions

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Lesson summary

GRADE 8 - Unit 5: Reactivity — HIA INTERNATIONAL notes: Compare metals and non-metals, use the pH scale and neutralisation, apply the reactivity series to displacement and extraction, and make and test salts.Metal — a shiny element that conducts heat and electricity; metals are o…

Exceptions
With universal indicator
No reaction
Ordering unknown metals
Blast furnace
Above carbon

Part 1 of 7Metals, non-metals and alloys

Metal

Metal a shiny element that conducts heat and electricity;
- metals are on the left of the Periodic Table and non-metals on the right.

Exceptions

Exceptions mercury is the only liquid metal and graphite is a non-metal that conducts electricity.

Bending

Bending metals can bend because their atoms are arranged in layers that can slide.

Alloy

Alloy a mixture of metals, e.g. brass = copper + zinc.

Brass

Brass hard, does not corrode and gold-coloured, so used for musical instruments, door handles and electrical plugs.

Part 2 of 7Acids and alkalis

Acids

Acids found in fizzy drinks, vinegar and car batteries.

Alkalis

Alkalis found in oven cleaners, soap, toothpaste and indigestion remedies.

Litmus

Litmus acids turn blue litmus red; alkalis turn red litmus blue.

Type	pH	Everyday examples	Litmus
Strong acid	0–3	Hydrochloric and sulfuric acid	Red
Weak acid	4–6	Lemon juice, vinegar	Red
Neutral	7	Pure water, salt solution	Purple
Weak alkali	8–10	Toothpaste, soap	Blue
Strong alkali	11–14	Oven cleaner, sodium hydroxide	Blue

Part 3 of 7Neutralisation

Equation

Equation acid + alkali → salt + water.

With universal indicator

With universal indicator add alkali drop by drop with stirring;
- the colour passes orange and yellow and you stop at green (pH 7).

Titration

Titration adding one solution to another until the reaction is exactly complete.

Part 4 of 7The reactivity series and displacement

Order

Order potassium, sodium, calcium, magnesium, aluminium, (carbon), zinc, iron, lead, (hydrogen), copper, silver, gold.

Displacement

Displacement a more reactive metal takes the place of a less reactive one in its compound.

No reaction

No reaction a less reactive metal cannot displace a more reactive one.

Ordering unknown metals

Ordering unknown metals the metal that displaces the most others is the most reactive.

Energy

Energy displacement is usually exothermic, with a larger temperature rise for a bigger reactivity gap.

Part 5 of 7Extraction and acids

Carbon

Carbon it lies between aluminium and zinc, so it displaces zinc, iron, tin, lead and copper from their oxides.

Blast furnace

Blast furnace iron oxide + carbon → iron + carbon dioxide.

Above carbon

Above carbon aluminium and magnesium cannot be extracted with carbon, so electrolysis is used.

Reaction with acids

Reaction with acids metals above hydrogen react with dilute acids to give a salt and hydrogen; metals below hydrogen do not.
- (copper, silver, gold)

Part 6 of 7Making salts

Sources

Sources salts are made by reacting acids with metals, metal oxides, hydroxides or carbonates.

Sulfates

Sulfates sulfuric acid makes sulfates, e.g. magnesium + sulfuric acid → magnesium sulfate + hydrogen.

Carbonates

Carbonates acid + carbonate → salt + water + carbon dioxide; limewater turns milky.

Crystals

Crystals evaporate some of the water slowly from the salt solution and leave to crystallise.

Part 7 of 7Equations

Word equation

Word equation shows reactants → products in words.

Balancing

Balancing check the atoms on each side; Mg + O₂ → MgO has two O on the left, so 2Mg + O₂ → 2MgO.

Key words

Key words chemical property, reactivity, oxidation, corrosion, rust, hydrogen, displacement.

Key terms

Term	Meaning
Alloy	A mixture of metals.
Neutralisation	An acid reacting with an alkali to form a salt and water.
Displacement reaction	A more reactive metal replacing a less reactive one in a compound.
Reactivity series	A list of metals from most to least reactive.
Salt	A compound formed when the hydrogen in an acid is replaced by a metal.
Indicator	A substance that changes colour in acids and alkalis.
pH	A measure of acidity or alkalinity.
Oxidation	A reaction with oxygen.

Avoid these mistakes

Saying all non-metals are insulators — graphite is a non-metal that conducts electricity.

Saying all metals are solid — mercury is a liquid metal.

Saying the pH of a strong acid is 14 — strong acids are pH 0–3; strong alkalis are 11–14.

Forgetting that displacement works only when the added metal is more reactive.

Writing the products of acid + carbonate without carbon dioxide.

Last updated: 12 October 2026