Titration is chemistry's most precise measurement technique. By slowly adding a solution of known concentration to one of unknown concentration, and watching for the exact moment the reaction completes — the equivalence point — chemists can determine the exact composition of any acid or base solution.
A Brief History
⚗️
Gay-Lussac (1778–1850) formalized volumetric analysis — what we now call titration — in the early 1800s. The word "titration" itself comes from French titre, meaning "standard" or "grade." Gay-Lussac also discovered the law of combining gas volumes. Indicator-based titration, using substances like phenolphthalein to signal the equivalence point by changing color, was developed and refined throughout the 19th century by analytical chemists seeking ever-greater precision in quantitative analysis.
Core Concept: The Equivalence Point
In an acid-base titration, a base (titrant) of known concentration is slowly added to an acid (analyte) of unknown concentration. The equivalence point is reached when moles of acid exactly equal moles of base:
M1V1 = M2V2
M₁ = molarity of acid (mol/L)
V₁ = volume of acid (L or mL)
M₂ = molarity of base (mol/L)
V₂ = volume of base added at equivalence point (L or mL)
Indicator: phenolphthalein is colorless in acid (pH < 8.2) and turns pink in base (pH > 8.2)
pH curve: starts low (acidic), rises slowly, then jumps sharply at the equivalence point
Before equivalence: excess acid in solution — pH remains low
After equivalence: excess base added — pH rises above 7, indicator turns deep pink
Key insight: The equivalence point is a chemical reality — it occurs when moles of acid = moles of base. The end point is what we observe — the indicator color change. In a well-conducted titration, the two coincide very closely.
Interactive Simulator
Add NaOH drop by drop and watch the pH rise. The flask solution changes color as you approach and pass the equivalence point.
NaOH Added0.0 mL
pH—
StatusPre-Eq.
Real-World Applications
💧
Water Quality Testing
Environmental agencies use acid-base titration to measure the alkalinity and acidity of drinking water, rivers, and lakes to detect pollution.
🍷
Food Industry
Winemakers and juice producers use titration to measure the titratable acidity of their products — a key quality control parameter that affects taste and preservation.
💊
Pharmaceutical Manufacturing
Drug manufacturers titrate active ingredients to verify that tablets and injections contain exactly the right concentration of the active compound.
🌧️
Environmental Monitoring
Acid rain monitoring uses titration to measure the sulfuric and nitric acid content of rainfall samples, tracking the impact of industrial emissions.
Practice Problems
Use M₁V₁ = M₂V₂ at the equivalence point. Keep units consistent (both mL or both L).
Easy1. At the equivalence point in a titration, moles of acid equal moles of base. True or False?
Hint: The equivalence point is defined as the point where the moles of titrant added exactly equal the moles of analyte present.
Easy2. Phenolphthalein indicator is colorless in acid. What color does it turn in base?
Hint: Phenolphthalein undergoes a structural change above pH 8.2, causing it to absorb visible light and appear pink/magenta.
Medium3. 25 mL of 0.1 M HCl is titrated with 0.1 M NaOH. How many mL of NaOH is needed to reach the equivalence point?
Hint: M₁V₁ = M₂V₂ → 0.1 × 25 = 0.1 × V₂ → V₂ = 25 mL. Same molarity means same volume.
Medium4. 20 mL of 0.5 M HCl needs to be neutralized with 0.25 M NaOH. How many mL of NaOH is required?
Challenge5. A student titrates 25 mL of an unknown acid with 0.2 M NaOH. It takes 31.5 mL of NaOH to reach the equivalence point. What is the molarity of the acid (to 3 decimal places)?