A titration finds the exact volume of acid that neutralises a volume of alkali. A pipette is used to measure 25.0 cm3 of the alkali accurately into a conical flask. A few drops of a suitable indicator are added. Phenolphthalein is pink in alkali and colourless in acid, and methyl orange is yellow in alkali and red in acid. Each changes colour sharply at the end-point.
The acid is put in a burette, and the starting reading is noted. Acid is run into the flask, which is swirled all the time. Near the end-point the acid is added dropwise, so that it does not overshoot. The titre is the final reading minus the starting reading. The titration is repeated until the results are concordant, which means they agree within 0.1 cm3.
To make a pure, dry salt, the titration is then repeated using the same volumes but without the indicator, because the indicator would contaminate the salt. The solution is heated to evaporate some of the water and left to cool so that crystals form. The crystals are filtered off, washed with a little cold distilled water and dried.
