titration
/ ty-TRAY-shun /
Imagine slowly pouring a known liquid, drop by careful drop, into an unknown one, watching for the exact instant it changes colour. That patient drip-and-watch is a titration — a way to find out exactly how much of something is in a solution by measuring how much of a known reactant it takes to use it all up.
In an acid–base titration you add a solution of known concentration (the titrant) from a burette into a measured sample, until the moles of acid and base exactly match. That balance point is the equivalence point, and an indicator or a pH meter signals when you reach it. From the volume you used and the known concentration, simple arithmetic gives the unknown concentration.
Titration matters because it turns a hard question — how much acid is in here? — into a precise volume measurement anyone can read off a burette. It underlies quality control in food, water, and medicine. The care needed is real: overshoot the colour change by one drop and your answer drifts, and the indicator must be chosen so its colour flip lines up with the true equivalence point.
To find the concentration of vinegar, you drip sodium hydroxide of known strength into it with a few drops of phenolphthalein; the moment the liquid turns faint pink, the acid is exactly used up.
Titration measures an unknown amount by the volume of a known reactant needed to match it.
Do not confuse the equivalence point with the endpoint. The equivalence point is where acid and base are chemically equal; the endpoint is where the indicator actually changes colour. A good titration chooses an indicator so these two nearly coincide.