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CHEMISTRY · ACIDS AND BASES
Acid–Base and pH
Explore the pH scale, observe indicator colours, and investigate how acids and bases neutralise one another.
1. Explore the pH scale
7.0
Neutral solution
0 · Acidic7 · Neutral14 · Alkaline
Hydrogen ion concentration (approx.)1 × 10⁻⁷ mol/L
Solution classificationNeutral
For dilute aqueous solutions at about 25°C, pH below 7 is acidic, pH 7 is neutral, and pH above 7 is alkaline.
2. Indicator colour test
Green · Neutral
Selected indicatorUniversal indicator
Expected colourGreen
Indicator colours are approximate. Actual colours can vary with concentration, lighting, and the particular indicator preparation.
3. Neutralisation simulation
Add acid and base to a model mixture. The simulation tracks equivalent amounts of acid and base, assuming a simple strong-acid/strong-base reaction with equal concentrations. It is a conceptual model, not a laboratory-grade pH calculator.
Acid added10 mL
Base added10 mL
Excess equivalent0 mL
Mixture stateNeutralised
Equal acid and base amounts: the idealised mixture is neutral.
4. Procedure
- Move the pH slider across the scale.
- Compare the colours of different indicators.
- Reset the mixture, then add acid and base.
- Observe what happens when their amounts become equal.
- Record your findings in the table.
5. Key ideas
- Acids increase hydronium ion concentration in water.
- Bases reduce hydronium concentration or increase hydroxide concentration.
- Neutralisation commonly produces water and a salt.
- Equal volumes do not always neutralise each other in real experiments; concentration and reaction stoichiometry matter.
6. Observation table
| # | pH | Classification | Indicator | Colour | Acid/Base (mL) |
|---|---|---|---|---|---|
| Adjust the pH or mixture, then record an observation. | |||||