Investigation 4: Designing a Titration
Designing a titration means choosing a reaction, an indicator that changes color right at the equivalence point, and a careful procedure so the volume of titrant used gives an accurate concentration.
A titration finds an unknown concentration by reacting it, drop by drop, with a solution of known concentration until the moles are exactly matched at the equivalence point. Because that moment happens at one precise volume, you need a signal that appears sharply right there, not gradually. That's why the pH curve has a steep vertical jump near equivalence: a tiny addition of titrant swings the pH by several units. An indicator works because it changes color over its own narrow pH range, so a good choice has that range landing inside the steep jump, meaning the color change (the endpoint) happens at essentially the same volume as the true equivalence point.
Designing a real titration means working backward from that goal. To find the acid content of fruit juice, you'd measure a known volume of juice, add a few drops of indicator, then slowly add standardized base from a buret while swirling, watching for the first permanent color change. You record that volume, use the base's known concentration and the stoichiometry of the neutralization to solve for moles of acid, then convert to concentration or percent acid by mass.
This topic sits alongside error analysis and experimental design in the lab unit because titration is where small procedural slips become large calculation errors. Every volume reading, every rinse step, and every drop past the endpoint feeds directly into a concentration calculation, so this investigation is really practice in connecting technique to the numbers that come out of it.
Key terms
- Equivalence point
- The volume at which moles of titrant added exactly match moles of the substance being titrated, based on reaction stoichiometry.
- Endpoint
- The volume at which the indicator visibly changes color, used as an experimental estimate of the equivalence point.
- Indicator
- A substance that changes color over a specific, narrow pH range, chosen to match the steep part of the titration curve.
- Standardized solution
- A solution whose exact concentration has been carefully determined, used as the known reagent in a titration.
- Systematic error
- A consistent procedural flaw, like a diluted titrant, that skews every result in the same direction.
Watch it explained
- How it worksHow do you pick an indicator whose color change lands inside the steep part of the curve?
- How it worksWalk me through designing a titration to find the acid content of a bottle of fruit juice.
- Common mistakeWhy isn't rinsing the buret with water instead of titrant a harmless shortcut?
- Going furtherWhat happens to the calculated concentration when you overshoot the endpoint by 1 mL?
Check yourself
End of topic.