Everything on the GCSE Chemistry Acids, Bases & Titration poster is written out below, section by section. Use it to search the sheet, copy parts into your own notes, or check a fact quickly.
Acids, alkali and the pH scale
Acids form H⁺ ions in water. Alkalis (soluble bases) form OH⁻ ions. Each pH unit is a factor of 10 change in H⁺ concentration. You can measure pH with universal indicator or a pH probe.
The pH scale runs from 0 (strongly acidic) through 7 (neutral) to 14 (strongly alkaline).
Neutralisation: H⁺ + OH⁻ → H₂O
Indicator colour changes
| Indicator | Acid | Alkali |
|---|---|---|
| Litmus | Red | Blue |
| Methyl orange | Red | Yellow |
| Phenolphthalein | Colourless | Pink |
Strong vs weak acids
- Strong acids (HCl, H₂SO₄, HNO₃) ionise fully in water.
- Weak acids (ethanoic, citric, carbonic) ionise partially, shown with a reversible arrow (⇌).
Strong acid (HCl): completely ionised - HCl → H⁺ + Cl⁻
Weak acid (CH₃COOH): partially ionised - CH₃COOH ⇌ H⁺ + CH₃COO⁻
- Concentrated/dilute describes how much acid is dissolved.
- Strong/weak describes how much ionises.
- Don't confuse them!
Acid reactions and salt naming
Acid + metal → salt + hydrogen
- Example: 2HCl + Mg → MgCl₂ + H₂
Acid + base/alkali → salt + water
- Example: H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O
Acid + carbonate → salt + water + CO₂
- Example: 2HCl + Na₂CO₃ → 2NaCl + H₂O + CO₂
Salt name comes from the acid
- HCl → chlorides
- H₂SO₄ → sulfates
- HNO₃ → nitrates
Titration method
Titration is used to find the exact volume of acid needed to neutralise a known volume of alkali.
- Pipette 25 cm³ of alkali into a conical flask. Add a few drops of indicator.
- Fill the burette with acid. Record the start reading.
- Add acid slowly, swirling.
- Near the end point, add acid dropwise until the indicator just changes colour.
- Record the end reading.
- Titre = end reading - start reading.
- Repeat until you get concordant titres (within 0.10 cm³). Mean the concordant values.
- The burette holds the acid.
- The conical flask holds the alkali and indicator.
- Endpoint: the point at which the indicator just changes colour.