Chapter 14 · Acids and Bases
14.6Acid–Base Titration: A Way to Quantify the Amount of Acid or Base
12 min · two checks
Predict
At the equivalence point of a titration, what is true?
The idea
- Calculate an unknown molarity from titration data.
- Distinguish equivalence point from endpoint.
A titration adds a solution of known concentration (the titrant) from a burette until the analyte is exactly consumed. The equivalence point is that exact stoichiometric match. The endpoint is the color change you see. A good indicator makes those two volumes nearly the same. Phenolphthalein is a common choice for strong acid–strong base work; it turns pink on the basic side.
The calculation is solution stoichiometry. Moles of known = M × V. Use the mole ratio to get moles of unknown. Divide by the unknown’s volume in liters. If the acid is diprotic and the base is NaOH, include the 2. Report molarity with the significant figures the volumes and the known concentration deserve. Rinsing the burette and reading the meniscus are lab skills; the algebra does not forgive a factor-of-two chemistry mistake.
Keep these
- Equivalence: stoichiometric moles, from the equation.
- Endpoint: the indicator’s signal, aimed at equivalence.
- Moles = M × V, then the mole ratio, then divide by volume.
Worked path
A 20.00 mL sample of H₂SO₄ requires 24.00 mL of 0.100 M NaOH. Find the sulfuric acid molarity. H₂SO₄ + 2 NaOH → products.
Observe
Moles NaOH = 0.02400 × 0.100 = 0.00240.