Acid-Base Titration is a fundamental quantitative laboratory technique used to determine the unknown concentration of a dissolved acid or base. By reacting a solution of unknown concentration with a solution of a precisely known concentration (the titrant), scientists can use the stoichiometry of the chemical reaction to calculate the exact molarity of the sample. This is the primary method used for everything from testing the acidity of wine to ensuring the potency of liquid antacids.

How Acid-Base Titration Works

The process relies on a controlled chemical “battle” where the point of victory is reached when the acid and base have perfectly neutralized each other.

1. Preparation A precise volume of the unknown solution (the analyte) is placed in an Erlenmeyer flask. A few drops of a pH indicator (like phenolphthalein) are added. Meanwhile, a long, graduated glass tube called a buret is filled with the titrant—the solution with a known concentration.

2. The Addition The stopcock of the buret is opened, allowing the titrant to flow into the flask. As the two liquids mix, a neutralization reaction occurs. For example, if you are titrating hydrochloric acid (HCl) with sodium hydroxide (NaOH), they react to form water and salt: HCl+NaOH→H2​O+NaCl

3. The Equivalence Point The goal is to reach the equivalence point, where the number of moles of added titrant is chemically equal to the number of moles of the substance in the unknown sample. At this exact moment, the acid and base have completely “cancelled” each other out.

4. The End Point Because the equivalence point is invisible, we rely on the end point. This is the moment the pH indicator permanently changes color (e.g., turning from clear to a very faint, persistent pink). This color change signals the scientist to stop the flow immediately.

5. Calculation By measuring exactly how many milliliters (V) of titrant were used from the buret, and knowing the titrant’s molarity (M), the concentration of the unknown can be calculated using the formula: Macid​×Vacid​=Mbase​×Vbase​

(Note: This assumes a 1:1 mole ratio; coefficients are added for other ratios.)