Acid–base titration

Theory

In titration, a solution of known concentration helps us find an unknown one. HCl and NaOH react in a 1:1 mole ratio. At the equivalence point, the amounts of acid and base that have reacted match this ratio.

We observe an indicator endpoint to estimate that point. Endpoint means the visible colour change; equivalence means the required reacting amounts, so they are different ideas. Here, phenolphthalein turns from colourless to a faint lasting pink with a small excess of base. Keep concentration and volume units consistent in the calculation.

cₐVₐ = cᵦVᵦ

This form applies to the 1:1 reaction: c is concentration in mol/L; use the same volume unit for both V values.