4.6 Introduction to Titration

What is a titration?

A titration is a lab technique used to determine the unknown concentration of a solution (the analyte) by reacting it with a solution of known concentration (the titrant). Titrant is added slowly from a burette until the reaction reaches the equivalence point, where moles of reactants have reacted in the stoichiometric ratio given by the balanced equation.

Indicators and the endpoint

An indicator is added to visually signal when the reaction is complete. It changes color at the endpoint, which should closely match the true equivalence point. For acid-base titrations, phenolphthalein is common, turning colorless to pink near neutral-to-basic pH. The volume of titrant added at the endpoint is used to calculate the unknown concentration.

Using titration data

At the equivalence point, moles of acid = moles of base (for a 1:1 reaction), using M₁V₁ = M₂V₂ when stoichiometry is 1:1. For other ratios, use mole ratios from the balanced equation. Data from titration (volume, known concentration) lets chemists calculate the unknown solution's molarity accurately.

Key terms

Titration

A technique that determines an unknown solution's concentration by reacting it with a solution of known concentration.

Titrant

The solution of known concentration added from the burette during a titration.

Analyte

The solution with unknown concentration being analyzed in a titration.

Equivalence point

The point where moles of reactants have combined in the exact stoichiometric ratio from the balanced equation.

Endpoint

The point in a titration where the indicator changes color, ideally very close to the equivalence point.

Try an AP-style question

25.0 mL of HCl is neutralized by 20.0 mL of 0.100 M NaOH. What is [HCl]?

1. 0.0500 M
2. 0.0800 M
3. 0.100 M
4. 0.125 M