Types of chemical reactions

Welcome to your study notes on the different ways chemical reactions can be classified. In this topic, we will look closely at what is happening to atoms, ions, and electrons during chemical changes.

What you'll learn

How to define and identify oxidation and reduction in terms of oxygen transfer and electron transfer.
The difference between strong, weak, dilute, and concentrated acids.
How acids react with metals, bases, and carbonates, and how to write their equations.
How the pH scale is mathematically linked to the concentration of hydrogen ions.

1. Oxidation and Reduction (Redox)

Historically, chemists classified reactions based on whether substances gained or lost oxygen. Today, we look deeper at what is happening to the electrons, but both levels of understanding are essential for your exam.

Oxidation and Reduction in terms of Oxygen

At a basic level, oxidation and reduction are opposites:

Definition

Oxidation and Reduction (Oxygen)

Oxidation is the gain of oxygen by a chemical species.
Reduction is the loss of oxygen from a chemical species.

Because these two processes always occur together in a chemical reaction, we call these reactions redox reactions.

To help us describe redox reactions, we use two key terms:

Oxidising agent: The substance that oxidises something else by donating oxygen to it. By doing this, the oxidising agent loses its own oxygen and is reduced.
Reducing agent: The substance that reduces something else by removing oxygen from it. By doing this, the reducing agent gains oxygen and is oxidised.

Let's look at a classic industrial reaction: the extraction of iron in the blast furnace.

\text{Fe}_2\text{O}_3(\text{s}) + 3\text{CO}(\text{g}) \to 2\text{Fe}(\text{l}) + 3\text{CO}_2(\text{g})

The iron(III) oxide ( $Fe2O3\text{Fe}_2\text{O}_3$ ) loses oxygen to become iron ( $Fe\text{Fe}$ ). Therefore, iron(III) oxide is reduced. It acts as the oxidising agent.
The carbon monoxide ( $CO\text{CO}$ ) gains oxygen to become carbon dioxide ( $CO2\text{CO}_2$ ). Therefore, carbon monoxide is oxidised. It acts as the reducing agent.

Oxidation and Reduction in terms of Electrons (Higher Tier Only)

At the Higher Tier, you must define oxidation and reduction in terms of electron transfer. This is particularly useful when reactions do not involve oxygen at all.

Key Idea

The OIL RIG Mnemonic

Use this famous mnemonic to remember electron transfer in redox reactions:

Oxidation Is Loss of electrons.
Reduction Is Gain of electrons.

To see this in action, we write ionic equations to show only the species that actually change their charge.

Example

Identifying redox species using electron transfer

State which species is oxidised and which is reduced when magnesium reacts with copper(II) sulfate solution:

\text{Mg}(\text{s}) + \text{CuSO}_4(\text{aq}) \to \text{MgSO}_4(\text{aq}) + \text{Cu}(\text{s})

Write the ionic equation. Split soluble ionic compounds into their individual aqueous ions to identify the spectator ions (ions that do not change). The sulfate ion ( $SO42−\text{SO}_4^{2-}$ ) remains unchanged, so we remove it:

\text{Mg}(\text{s}) + \text{Cu}^{2+}(\text{aq}) \to \text{Mg}^{2+}(\text{aq}) + \text{Cu}(\text{s})

Write the half-equation for the magnesium species. Track the change from reactant to product:

\text{Mg}(\text{s}) \to \text{Mg}^{2+}(\text{aq}) + 2\text{e}^-

Because magnesium has lost two electrons to become a positive ion, it has undergone oxidation. Magnesium ( $Mg\text{Mg}$ ) is the reducing agent because it gave electrons away.

Write the half-equation for the copper species. Track the change from reactant to product:

\text{Cu}^{2+}(\text{aq}) + 2\text{e}^- \to \text{Cu}(\text{s})

Because the copper(II) ion has gained two electrons, it has undergone reduction. The $Cu2+\text{Cu}^{2+}$ ion is the oxidising agent because it accepted electrons.

2. Acids, Alkalis, and Neutralisation

What makes a chemical an acid or an alkali? The answer lies in the ions they release when dissolved in water.

What is an Acid?

Acids are substances that release hydrogen ions, $H+(aq)\text{H}^+(\text{aq})$ , when they dissolve in water. A hydrogen ion is simply a single proton! For example, when hydrogen chloride gas dissolves in water, it splits (dissociates) into ions:

\text{HCl}(\text{g}) \xrightarrow{\text{water}} \text{H}^+(\text{aq}) + \text{Cl}^-(\text{aq})

What is an Alkali?

An alkali is a soluble base. Alkalis release hydroxide ions, $OH−(aq)\text{OH}^-(\text{aq})$ , when they dissolve in water. For example:

\text{NaOH}(\text{s}) \xrightarrow{\text{water}} \text{Na}^+(\text{aq}) + \text{OH}^-(\text{aq})

Common Mistake

Bases vs. Alkalis

Do not confuse the terms "base" and "alkali". All alkalis are bases, but only soluble bases are alkalis. For example, copper(II) oxide is an insoluble base, so it is not an alkali. Sodium hydroxide is a soluble base, so it is an alkali.

Neutralisation

When an acid reacts with a base (or an alkali), they neutralise each other to produce a salt and water:

\text{Acid} + \text{Base} \to \text{Salt} + \text{Water}

At the ionic level, aqueous neutralisation is always the reaction between hydrogen ions from the acid and hydroxide ions from the alkali to form water molecules.

Key Idea

The Ionic Equation for Neutralisation

Any neutralisation reaction between an acid and an alkali can be simplified to this ionic equation:

\text{H}^+(\text{aq}) + \text{OH}^-(\text{aq}) \to \text{H}_2\text{O}(\text{l})

In your practical work (specifically PAG C7), you will prepare pure, dry crystals of a soluble salt using this concept. You react an acid with an excess of an insoluble base (like copper(II) oxide), filter off the unreacted solid, and then heat the filtrate to evaporate the water and leave pure salt crystals.

3. Reactions of Acids with Metals and Carbonates

Acids undergo predictable reactions with metals and metal carbonates. You must be able to write balanced chemical equations to describe these reactions.

Acid + Metal

When a metal reacts with an acid, a redox reaction occurs to produce a salt and hydrogen gas:

\text{Acid} + \text{Metal} \to \text{Salt} + \text{Hydrogen}

Example: Zinc reacting with hydrochloric acid:

\text{Zn}(\text{s}) + 2\text{HCl}(\text{aq}) \to \text{ZnCl}_2(\text{aq}) + \text{H}_2(\text{g})

Acid + Carbonate

When a carbonate reacts with an acid, it produces a salt, water, and carbon dioxide gas (which causes fizzing):

\text{Acid} + \text{Metal Carbonate} \to \text{Salt} + \text{Water} + \text{Carbon Dioxide}

Example: Calcium carbonate reacting with nitric acid:

\text{CaCO}_3(\text{s}) + 2\text{HNO}_3(\text{aq}) \to \text{Ca(NO}_3)_2(\text{aq}) + \text{H}_2\text{O}(\text{l}) + \text{CO}_2(\text{g})

4. Strong vs. Weak and Dilute vs. Concentrated Acids (Higher Tier Only)

Many students confuse the "strength" of an acid with its "concentration". They mean completely different things.

Acid Strength (Degree of Ionisation)

Acid strength refers to how easily an acid splits up into ions when dissolved in water.

Strong Acids: Fully ionise (completely dissociate) in water. Every single acid molecule splits up to release $H+\text{H}^+$ ions.

\text{HCl}(\text{aq}) \to \text{H}^+(\text{aq}) + \text{Cl}^-(\text{aq})

(Note the single-headed arrow showing the reaction goes to completion).

Weak Acids: Only partially ionise in water. Only a tiny fraction of the molecules split up, while the rest remain as intact, neutral molecules.

\text{CH}_3\text{COOH}(\text{aq}) \rightleftharpoons \text{CH}_3\text{COO}^-(\text{aq}) + \text{H}^+(\text{aq})

(Note the reversible arrow, showing a dynamic equilibrium exists between the molecules and the ions).

Acid Concentration

Concentration is a measure of the amount of acid substance dissolved in a given volume of solution (typically measured in moles per cubic decimetre, $mol/dm3\text{mol/dm}^3$ ).

Concentrated acid: A large number of moles of acid dissolved per cubic decimetre of water.
Dilute acid: A small number of moles of acid dissolved per cubic decimetre of water.

Strong vs Weak Acid Ionisation

Common Mistake

Confusing strength with concentration

Do not use "strong" to mean "concentrated". You can have a concentrated weak acid (e.g., a high concentration of ethanoic acid molecules, where only a small percentage split into ions) or a dilute strong acid (e.g., a low concentration of hydrochloric acid, where every single molecule has split into ions).

5. pH and Hydrogen Ion Concentration

The pH scale measures how acidic or alkaline a solution is.

pH < 7: Acidic (high concentration of $H+\text{H}^+$ ions)
pH 7: Neutral
pH > 7: Alkaline (high concentration of $OH−\text{OH}^-$ ions)

Measuring pH

At the Higher Tier, you need to know how we measure pH in the laboratory:

Universal Indicator: A mixture of indicators that changes through a range of colours. It is cheap and easy but subjective because matching colors to a chart by eye can lead to human error.
pH Meter: An electronic probe that measures pH directly. This is much more precise and objective because it provides a digital numerical value (e.g., $3.45$ ) instead of a colour approximation.

The pH Scale and $H+\text{H}^+$ Concentration (Higher Tier Only)

The pH scale is logarithmic. This means the numerical value of pH is directly related to the concentration of $H+\text{H}^+$ ions by a factor of ten.

Key Idea

The Factor-of-Ten Rule

As the concentration of hydrogen ions ( $H+\text{H}^+$ ) increases by a factor of 10, the pH value decreases by 1.

Conversely, as the concentration of hydrogen ions ( $H+\text{H}^+$ ) decreases by a factor of 10, the pH value increases by 1.

This relationship can be represented as:

\text{Change in } [\text{H}^+] = 10^{-\Delta\text{pH}}

Let's look at how to apply this rule to calculations.

Example

Calculating pH change upon dilution

A sample of sulfuric acid has a pH of 2. It is diluted with water until its hydrogen ion concentration is reduced to $11000\frac{1}{1000}$ of its original value. Calculate the new pH of the solution.

Identify the factor of change in $H+\text{H}^+$ concentration. The concentration of $H+\text{H}^+$ has decreased by a factor of $1000$ .
Express the factor of change as a power of 10.

\times 10 \times 10 = 10^3

This represents three successive "tenfold" decreases in concentration.

Calculate the change in pH. Since each tenfold decrease in $H+\text{H}^+$ concentration increases the pH by exactly 1, a $10^3$ decrease will increase the pH by 3 units.

\text{New pH} = \text{Original pH} + 3 = 2 + 3 = 5

The new pH of the solution is 5.

Exam technique

In the exam

Look at the arrow in the equation: If you are asked to identify a strong or weak acid from an equation, check the arrow. A single arrow ( $→\to$ ) indicates a strong acid; a reversible arrow ( $⇌\rightleftharpoons$ ) indicates a weak acid.
Watch your charges in redox: In electron-transfer half-equations, make sure your charges balance. For example, $Mg→Mg2++2e−\text{Mg} \to \text{Mg}^{2+} + 2\text{e}^-$ is balanced because the net charge on both sides is 0.
Use ionic equations for neutralisation: If a question asks for "the ionic equation for neutralisation", always write $H+(aq)+OH−(aq)→H2O(l)\text{H}^+(\text{aq}) + \text{OH}^-(\text{aq}) \to \text{H}_2\text{O}(\text{l})$ . Do not write the full spectator ions unless specifically asked.

Self review

Check yourself

Write the half-equation showing the reduction of a iron(III) ion ( $Fe3+\text{Fe}^{3+}$ ) to an iron(II) ion ( $Fe2+\text{Fe}^{2+}$ ).
Explain the difference between a concentrated weak acid and a dilute strong acid.
If an acid solution with a pH of 4 is diluted so that its hydrogen ion concentration decreases by a factor of 100, what is its new pH?

Types of chemical reactions

Welcome to your study notes on the different ways chemical reactions can be classified. In this topic, we will look closely at what is happening to atoms, ions, and electrons during chemical changes.

What you'll learn

How to define and identify oxidation and reduction in terms of oxygen transfer and electron transfer.
The difference between strong, weak, dilute, and concentrated acids.
How acids react with metals, bases, and carbonates, and how to write their equations.
How the pH scale is mathematically linked to the concentration of hydrogen ions.

1. Oxidation and Reduction (Redox)

Oxidation and Reduction in terms of Oxygen

At a basic level, oxidation and reduction are opposites:

Definition

Oxidation and Reduction (Oxygen)

Oxidation is the gain of oxygen by a chemical species.
Reduction is the loss of oxygen from a chemical species.

Because these two processes always occur together in a chemical reaction, we call these reactions redox reactions.

To help us describe redox reactions, we use two key terms:

Oxidising agent: The substance that oxidises something else by donating oxygen to it. By doing this, the oxidising agent loses its own oxygen and is reduced.
Reducing agent: The substance that reduces something else by removing oxygen from it. By doing this, the reducing agent gains oxygen and is oxidised.

Let's look at a classic industrial reaction: the extraction of iron in the blast furnace.

\text{Fe}_2\text{O}_3(\text{s}) + 3\text{CO}(\text{g}) \to 2\text{Fe}(\text{l}) + 3\text{CO}_2(\text{g})

The iron(III) oxide ( $Fe2O3\text{Fe}_2\text{O}_3$ ) loses oxygen to become iron ( $Fe\text{Fe}$ ). Therefore, iron(III) oxide is reduced. It acts as the oxidising agent.
The carbon monoxide ( $CO\text{CO}$ ) gains oxygen to become carbon dioxide ( $CO2\text{CO}_2$ ). Therefore, carbon monoxide is oxidised. It acts as the reducing agent.

Oxidation and Reduction in terms of Electrons (Higher Tier Only)

At the Higher Tier, you must define oxidation and reduction in terms of electron transfer. This is particularly useful when reactions do not involve oxygen at all.

Key Idea

The OIL RIG Mnemonic

Use this famous mnemonic to remember electron transfer in redox reactions:

Oxidation Is Loss of electrons.
Reduction Is Gain of electrons.

To see this in action, we write ionic equations to show only the species that actually change their charge.

Example

Identifying redox species using electron transfer

State which species is oxidised and which is reduced when magnesium reacts with copper(II) sulfate solution:

\text{Mg}(\text{s}) + \text{CuSO}_4(\text{aq}) \to \text{MgSO}_4(\text{aq}) + \text{Cu}(\text{s})

Write the ionic equation. Split soluble ionic compounds into their individual aqueous ions to identify the spectator ions (ions that do not change). The sulfate ion ( $SO42−\text{SO}_4^{2-}$ ) remains unchanged, so we remove it:

\text{Mg}(\text{s}) + \text{Cu}^{2+}(\text{aq}) \to \text{Mg}^{2+}(\text{aq}) + \text{Cu}(\text{s})

Write the half-equation for the magnesium species. Track the change from reactant to product:

\text{Mg}(\text{s}) \to \text{Mg}^{2+}(\text{aq}) + 2\text{e}^-

Because magnesium has lost two electrons to become a positive ion, it has undergone oxidation. Magnesium ( $Mg\text{Mg}$ ) is the reducing agent because it gave electrons away.

Write the half-equation for the copper species. Track the change from reactant to product:

\text{Cu}^{2+}(\text{aq}) + 2\text{e}^- \to \text{Cu}(\text{s})

Because the copper(II) ion has gained two electrons, it has undergone reduction. The $Cu2+\text{Cu}^{2+}$ ion is the oxidising agent because it accepted electrons.

2. Acids, Alkalis, and Neutralisation

What makes a chemical an acid or an alkali? The answer lies in the ions they release when dissolved in water.

What is an Acid?

\text{HCl}(\text{g}) \xrightarrow{\text{water}} \text{H}^+(\text{aq}) + \text{Cl}^-(\text{aq})

What is an Alkali?

An alkali is a soluble base. Alkalis release hydroxide ions, $OH−(aq)\text{OH}^-(\text{aq})$ , when they dissolve in water. For example:

\text{NaOH}(\text{s}) \xrightarrow{\text{water}} \text{Na}^+(\text{aq}) + \text{OH}^-(\text{aq})

Common Mistake

Bases vs. Alkalis

Neutralisation

When an acid reacts with a base (or an alkali), they neutralise each other to produce a salt and water:

\text{Acid} + \text{Base} \to \text{Salt} + \text{Water}

At the ionic level, aqueous neutralisation is always the reaction between hydrogen ions from the acid and hydroxide ions from the alkali to form water molecules.

Key Idea

The Ionic Equation for Neutralisation

Any neutralisation reaction between an acid and an alkali can be simplified to this ionic equation:

\text{H}^+(\text{aq}) + \text{OH}^-(\text{aq}) \to \text{H}_2\text{O}(\text{l})

3. Reactions of Acids with Metals and Carbonates

Acids undergo predictable reactions with metals and metal carbonates. You must be able to write balanced chemical equations to describe these reactions.

Acid + Metal

When a metal reacts with an acid, a redox reaction occurs to produce a salt and hydrogen gas:

\text{Acid} + \text{Metal} \to \text{Salt} + \text{Hydrogen}

Example: Zinc reacting with hydrochloric acid:

\text{Zn}(\text{s}) + 2\text{HCl}(\text{aq}) \to \text{ZnCl}_2(\text{aq}) + \text{H}_2(\text{g})

Acid + Carbonate

When a carbonate reacts with an acid, it produces a salt, water, and carbon dioxide gas (which causes fizzing):

\text{Acid} + \text{Metal Carbonate} \to \text{Salt} + \text{Water} + \text{Carbon Dioxide}

Example: Calcium carbonate reacting with nitric acid:

\text{CaCO}_3(\text{s}) + 2\text{HNO}_3(\text{aq}) \to \text{Ca(NO}_3)_2(\text{aq}) + \text{H}_2\text{O}(\text{l}) + \text{CO}_2(\text{g})

4. Strong vs. Weak and Dilute vs. Concentrated Acids (Higher Tier Only)

Many students confuse the "strength" of an acid with its "concentration". They mean completely different things.

Acid Strength (Degree of Ionisation)

Acid strength refers to how easily an acid splits up into ions when dissolved in water.

Strong Acids: Fully ionise (completely dissociate) in water. Every single acid molecule splits up to release $H+\text{H}^+$ ions.

\text{HCl}(\text{aq}) \to \text{H}^+(\text{aq}) + \text{Cl}^-(\text{aq})

(Note the single-headed arrow showing the reaction goes to completion).

Weak Acids: Only partially ionise in water. Only a tiny fraction of the molecules split up, while the rest remain as intact, neutral molecules.

\text{CH}_3\text{COOH}(\text{aq}) \rightleftharpoons \text{CH}_3\text{COO}^-(\text{aq}) + \text{H}^+(\text{aq})

(Note the reversible arrow, showing a dynamic equilibrium exists between the molecules and the ions).

Acid Concentration

Concentration is a measure of the amount of acid substance dissolved in a given volume of solution (typically measured in moles per cubic decimetre, $mol/dm3\text{mol/dm}^3$ ).

Concentrated acid: A large number of moles of acid dissolved per cubic decimetre of water.
Dilute acid: A small number of moles of acid dissolved per cubic decimetre of water.

Strong vs Weak Acid Ionisation

Common Mistake

Confusing strength with concentration

5. pH and Hydrogen Ion Concentration

The pH scale measures how acidic or alkaline a solution is.

pH < 7: Acidic (high concentration of $H+\text{H}^+$ ions)
pH 7: Neutral
pH > 7: Alkaline (high concentration of $OH−\text{OH}^-$ ions)

Measuring pH

At the Higher Tier, you need to know how we measure pH in the laboratory:

Universal Indicator: A mixture of indicators that changes through a range of colours. It is cheap and easy but subjective because matching colors to a chart by eye can lead to human error.
pH Meter: An electronic probe that measures pH directly. This is much more precise and objective because it provides a digital numerical value (e.g., $3.45$ ) instead of a colour approximation.

The pH Scale and $H+\text{H}^+$ Concentration (Higher Tier Only)

The pH scale is logarithmic. This means the numerical value of pH is directly related to the concentration of $H+\text{H}^+$ ions by a factor of ten.

Key Idea

The Factor-of-Ten Rule

As the concentration of hydrogen ions ( $H+\text{H}^+$ ) increases by a factor of 10, the pH value decreases by 1.

Conversely, as the concentration of hydrogen ions ( $H+\text{H}^+$ ) decreases by a factor of 10, the pH value increases by 1.

This relationship can be represented as:

\text{Change in } [\text{H}^+] = 10^{-\Delta\text{pH}}

Let's look at how to apply this rule to calculations.

Example

Calculating pH change upon dilution

A sample of sulfuric acid has a pH of 2. It is diluted with water until its hydrogen ion concentration is reduced to $11000\frac{1}{1000}$ of its original value. Calculate the new pH of the solution.

Identify the factor of change in $H+\text{H}^+$ concentration. The concentration of $H+\text{H}^+$ has decreased by a factor of $1000$ .
Express the factor of change as a power of 10.

\times 10 \times 10 = 10^3

This represents three successive "tenfold" decreases in concentration.

Calculate the change in pH. Since each tenfold decrease in $H+\text{H}^+$ concentration increases the pH by exactly 1, a $10^3$ decrease will increase the pH by 3 units.

\text{New pH} = \text{Original pH} + 3 = 2 + 3 = 5

The new pH of the solution is 5.

Exam technique

In the exam

Look at the arrow in the equation: If you are asked to identify a strong or weak acid from an equation, check the arrow. A single arrow ( $→\to$ ) indicates a strong acid; a reversible arrow ( $⇌\rightleftharpoons$ ) indicates a weak acid.
Watch your charges in redox: In electron-transfer half-equations, make sure your charges balance. For example, $Mg→Mg2++2e−\text{Mg} \to \text{Mg}^{2+} + 2\text{e}^-$ is balanced because the net charge on both sides is 0.
Use ionic equations for neutralisation: If a question asks for "the ionic equation for neutralisation", always write $H+(aq)+OH−(aq)→H2O(l)\text{H}^+(\text{aq}) + \text{OH}^-(\text{aq}) \to \text{H}_2\text{O}(\text{l})$ . Do not write the full spectator ions unless specifically asked.

Self review

Check yourself

Write the half-equation showing the reduction of a iron(III) ion ( $Fe3+\text{Fe}^{3+}$ ) to an iron(II) ion ( $Fe2+\text{Fe}^{2+}$ ).
Explain the difference between a concentrated weak acid and a dilute strong acid.
If an acid solution with a pH of 4 is diluted so that its hydrogen ion concentration decreases by a factor of 100, what is its new pH?

Types of chemical reactions

What you'll learn

1. Oxidation and Reduction (Redox)

Oxidation and Reduction in terms of Oxygen

Oxidation and Reduction in terms of Electrons (Higher Tier Only)

2. Acids, Alkalis, and Neutralisation

What is an Acid?

What is an Alkali?

Neutralisation

3. Reactions of Acids with Metals and Carbonates

Acid + Metal

Acid + Carbonate

4. Strong vs. Weak and Dilute vs. Concentrated Acids (Higher Tier Only)

Acid Strength (Degree of Ionisation)

Acid Concentration

5. pH and Hydrogen Ion Concentration

Measuring pH

The pH Scale and $H+\text{H}^+$ Concentration (Higher Tier Only)

Recap questions

You've reached the end

Types of chemical reactions

What you'll learn

1. Oxidation and Reduction (Redox)

Oxidation and Reduction in terms of Oxygen

Oxidation and Reduction in terms of Electrons (Higher Tier Only)

2. Acids, Alkalis, and Neutralisation

What is an Acid?

What is an Alkali?

Neutralisation

3. Reactions of Acids with Metals and Carbonates

Acid + Metal

Acid + Carbonate

4. Strong vs. Weak and Dilute vs. Concentrated Acids (Higher Tier Only)

Acid Strength (Degree of Ionisation)

Acid Concentration

5. pH and Hydrogen Ion Concentration

Measuring pH

The pH Scale and $H+\text{H}^+$ Concentration (Higher Tier Only)

Recap questions

You've reached the end

Types of chemical reactions

What you'll learn

1. Oxidation and Reduction (Redox)

Oxidation and Reduction in terms of Oxygen

Oxidation and Reduction in terms of Electrons (Higher Tier Only)

2. Acids, Alkalis, and Neutralisation

What is an Acid?

What is an Alkali?

Neutralisation

3. Reactions of Acids with Metals and Carbonates

Acid + Metal

Acid + Carbonate

4. Strong vs. Weak and Dilute vs. Concentrated Acids (Higher Tier Only)

Acid Strength (Degree of Ionisation)

Acid Concentration

5. pH and Hydrogen Ion Concentration

Measuring pH

The pH Scale and H+\text{H}^+H+ Concentration (Higher Tier Only)

Recap questions

You've reached the end

Types of chemical reactions Revision Guide

Types of chemical reactions

What you'll learn

1. Oxidation and Reduction (Redox)

Oxidation and Reduction in terms of Oxygen

Oxidation and Reduction in terms of Electrons (Higher Tier Only)

2. Acids, Alkalis, and Neutralisation

What is an Acid?

What is an Alkali?

Neutralisation

3. Reactions of Acids with Metals and Carbonates

Acid + Metal

Acid + Carbonate

4. Strong vs. Weak and Dilute vs. Concentrated Acids (Higher Tier Only)

Acid Strength (Degree of Ionisation)

Acid Concentration

5. pH and Hydrogen Ion Concentration

Measuring pH

The pH Scale and H+\text{H}^+H+ Concentration (Higher Tier Only)

Recap questions

You've reached the end

Types of chemical reactions Revision Guide

The pH Scale and $H+\text{H}^+$ Concentration (Higher Tier Only)

The pH Scale and $H+\text{H}^+$ Concentration (Higher Tier Only)