permanganate titration
/ per-MANG-guh-nate ty-tray-shun /
Picture a deep purple ink so vivid that a single drop colours a whole beaker — and that colour vanishes the instant it reacts. Permanganate titration uses that dramatic, self-announcing dye as both the reagent and its own signal.
A permanganate titration is a redox titration that uses potassium permanganate, a strong oxidising agent, as the titrant. As long as there is analyte left to oxidise, each added drop loses its purple and turns colourless; once the analyte is used up, the very next drop tints the solution a lasting pale pink, marking the end point.
It matters because permanganate is cheap, powerful, and acts as its own indicator, making it a classic way to measure reducing substances like iron(II), oxalate, or hydrogen peroxide. Its honest drawbacks: the solution is not stable enough to be a primary standard, so it must be standardized, and it usually needs an acidic medium to oxidise cleanly.
To check the strength of hydrogen peroxide, an acidified sample is titrated with permanganate; the purple drops decolourise on contact until, at the end point, one drop leaves a faint pink that does not fade.
Its own colour is the indicator: purple in, colourless out, until a lasting pink.
Because permanganate is not stable enough to be a primary standard, its solution must be standardized — commonly against pure sodium oxalate. Use hydrochloric acid with care, as chloride can be oxidised too and cause an error; sulfuric acid is preferred.