SCI UNIT 5 - Reactivity

Displacement, Salts, Reactivity Series

Reactivity is the tendency of a substance to undergo a chemical change or reaction, either alone or with other materials, often releasing energy in the process. It measures how easily atoms, molecules, or compounds interact, with highly reactive substances (like cesium or fluorine) reacting vigorously, while noble gases are inert. 

What is reactivity?

The reactivity series is an ordered list of metals—from most to least reactive—based on their tendency to lose electrons (forming positive ions) and react with water, acids, and oxygen. It acts as a predictive tool for displacement reactions, where higher-placed metals displace lower ones from compounds. 

Shows metals placed in order of reactivity with the most reactive metal at the top.

What is the reactivity series?

A displacement reaction is a reaction wherein a more reactive element will displace or “push out” a less reactive element from a compound, and takes its place. The less reactive element is now left pure and uncombined.

What is a displacement reaction?

A salt is a compound that forms when the hydrogen atom in an acid is replaced by a metal.

Salts consist of an anion (-) part which comes from the acid while the cation (+) part comes from bases.

What is a salt?

An acid is a substance with a pH level lower than 7, it tastes sour and follows the rule of B.R.A, wherein blue litmus paper turns red, indicating that the substance is acidic.

Strong acids include nitric acid, sulfuric acid and hydrochloric acid.

Weak acids include carbonic acid (in soda, forms when carbon dioxide reacts with water), citric acid (salts formed using citric acid are called citrates), ascorbic acid and salicylic acid.

What is an acid?

A base is a substance with a pH level higher than 7, it tastes bitter and it feels slippery, and is corrosive to the skin. It follows the rule of R.B.B, where in red litmus paper turns blue, indicating that the substance is base.

Common bases include metal oxides.

Strong bases include: Sodium Hydroxide, Potassium Hydroxide, and Calcium Hydroxide

Weak bases include: Ammonia, baking soda, and magnesium hydroxide.

What is a base?

It refers to a substance’s ability to dissolve in a liquid, usually water.

Define soluble

A substance that cannot dissolve in a particular solvent.

Define insoluble

Potassium (most reactive)

Sodium

Calcium

Magnesium

Aluminium

Carbon

Zinc

Iron

Tin

Lead

Hydrogen

Copper

Silver

Gold

Platinum (least reactive)

List the full reactivity series, with hydrogen, carbon and the other metals.

Zinc, iron, tin, lead and copper

What metals can be displaced by carbon?

1. Thermite reaction: A displacement reaction between aluminium and iron oxide. Used to weld railway lines together by igniting the mixture.

Give examples of displacement reactions.

1. Copper sulfate

2. Magnesium nitrate

3. Zinc sulfate

4. Iron sulfate

What are some common metal salt solutions?

Hydrochloric acid → HCl

Sulfuric acid → H2SO4

Nitric acid → HNO3

CO3 → CARBONATE

SO4 → SULFATE

NO3 → NITRATE

CL → CHLORIDE

Common acids and salts ending names

Uses of Salts:

• Agricultural: Fertilisers, pesticides

• Industrial: Film and photography paper

• Medical: Plaster and antiseptic

• Gymnastics: Uses magnesium carbonate so they don’t slip on their apparatus

• Chalk: Made from calcium sulfate

• Dyes: Can use aluminium sulfate

• Food: Sodium chloride is used as common table salt in flavouring food

• Soya seeds: Are coated with copper sulfate

What can salts be used for?

acid + metal → salt + hydrogen

Give the word equation for the reaction between METALS and ACIDS.

acid + metal oxide → salt + water

Metal oxides are basic in nature. Soluble metal bases form alkalis when they dissolve in water.

They do not produce hydrogen gas in reactions between metal oxides and acids because the metal is already combined with oxygen. This type of reaction is called a neutralisation reaction.

Give the general word equation for the reaction between METAL OXIDES and ACIDS.

acid + metal carbonate → salt + carbon dioxide + water

Give the word equation for the reaction between a METAL CARBONATE and a ACID.

alkali + acid → salt + water

Give the word equation for a neutralisation reaction between an ALKALI and a ACID

Metals like magnesium, iron and zinc are used to prepare salts as sodium and potassium will react violently.

What metals are usually used to prepare salts?