How to use: The burette holds 1.0 M sodium hydroxide (NaOH) and the
flask holds 20 mL hydrochloric acid (HCl). Add base with the buttons — use single
drops to zoom in on the endpoint. The flask liquid is colourless with
phenolphthalein… until it suddenly turns pink.
The graph plots pH (0–14) against base added; the dashed line is the
equivalence point where the acid and base are exactly balanced.
Notice: the pH creeps up slowly at first, then spikiness around the equivalence point
— a single drop can jump the pH from about 3 to 11. That part of the curve is where the
indicator changes colour. The equivalence volume you read equals the acid concentration
times 20 mL, so titration lets you measure a concentration you can't see.