The pH Scale and Neutralisation
Learning Objectives
The pH Scale and Neutralisation
Learning Objectives
Key Vocabulary
Neutralisation
Reaction between an acid and a base, producing water and a salt at pH 7.
Dissociation
The splitting of a compound into separate positive and negative aqueous ions.
The Continuous pH Spectrum
Indicators vs Digital Probes
Universal Indicator
A chemical dye mixture that changes colour across the full pH range
Limitation: Subjective colour matching can be inaccurate for intermediate values.
Digital pH Probe
An electronic sensor that measures electrical potential across a glass to calculate hydrogen ion activity.
Advantage: Eliminates human bias and measures 2 d.p (e.g. pH 7.35).
Sub-Microscopic Particles in Water
PARTICLE MODEL
📌
The Ionic Neutralisation Equation
Predicting Products and Spectator Ions
1
2
3
4
Check Your Understanding
Which ions form water to make pH 7? Hint: focus on hydrogen and hydroxide ions. Optional stretch: why do the other ions stay unchanged?
Hydrogen ions and hydroxide ions react to form neutral liquid water molecules.
Sodium and chloride ions react vigorously to neutralise each other.
Universal indicator forces the solution to reach an equal balance.
The acid dissolves the alkali so no ions remain in the water.
1
2
3
4
Check Your Understanding
Which ions form water to make pH 7? Hint: focus on hydrogen and hydroxide ions. Optional stretch: why do the other ions stay unchanged?
Hydrogen ions and hydroxide ions react to form neutral liquid water molecules.
Sodium and chloride ions react vigorously to neutralise each other.
Universal indicator forces the solution to reach an equal balance.
The acid dissolves the alkali so no ions remain in the water.
✓
1
2
3
4