Knowledge Organiser: Titrations
Key Terms
- Titre: volume added from burette (cm³)
- Concordant: titres within 0.10 cm³
- Endpoint: permanent colour change
- Burette: graduated tube, ±0.05 cm³
- Pipette: fixed volume transfer (25.0 cm³)
- n = c × V: moles from concentration
Must-Know Facts
- Indicator goes in conical flask, not burette
- Read bottom of meniscus at eye level
- Discard rough titration; average concordant results only
- Phenolphthalein: colourless → pink (acid → alkali)
- Methyl orange: red → yellow (acid → alkali)
- Higher Tier: 3-step calculation (n, ratio, c)
Key Equations
- n = c × V (moles = concentration × volume in dm³)
- V(dm³) = V(cm³) ÷ 1000
- c = n ÷ V (find unknown concentration after using mole ratio)
Common Mistakes
- Using volume in cm³ without converting: n = c × V requires volume in dm³ — always divide cm³ by 1000 first
- Averaging all titres including the rough: The rough titration is discarded — only average the concordant results (within 0.10 cm³ of each other)
- Forgetting the mole ratio step: After finding moles of one substance, use the equation's mole ratio before calculating the unknown concentration
- Putting indicator in burette: Indicator always goes in the conical flask — it stays with the solution being titrated, not the solution being added
Memory Aid
- Phenolphthalein: colourless in acid → PINK in alkali. Remember: "Phenol turns PINK in base."
- Methyl orange: RED in acid → yellow in alkali. Remember: "Methyl goes RED in acid."
- Litmus: red in acid, blue in alkali (not used in titrations — colour change is not sharp enough).