Titration apparatus and chemicals. Footage of the apparatus and chemicals used in an acid-base titration. At left is a conical flask below a burette that is mounted on a stand. At right are the chemicals used: hydrochloric acid and sodium hydroxide (a base), with the indicator phenolphthalein. A solution of hydrochloric acid is in the flask, with a few drops of the indicator added. Sodium hydroxide solution will be slowly added from the burette and the flask swirled to mix the chemicals. As the mixture in the flask approaches its endpoint (when the acid and base are exactly neutralised) adding further amounts of base turns the solution alkaline. This causes the indicator to show as purple.