Methyl orange is an acid-base indicator, in acid it turns red and in a base it turns yellow.
Potentiometric titration is a volumetric method in which the potential between two electrodes is measured (referent and indicator electrode) as a function of the added reagent volume. Types of potentiometric titrations for the determination of analytes in photoprocessing solutions include acid-base, redox, precipitation, and complexometric.
Potentiometric titrations are preferred to manual titrations, since they are more accurate and precise. They are also more easily adapted to automation, where automated titration systems can process larger volumes of samples with minimal analyst involvement.
A titration curve has a characteristic sigmoid curve. The part of the curve that has the maximum change marks the equivalence point of the titration. The first derivative, ΔE/ΔV, is the slope of the curve, and the endpoint occurs at the volume, V', where ΔE/ΔV has the maximum value.
Winkler’s method was once a common method used to determine the dissolved oxygen concentration by titration. Now rarely used due to the accuracy and low price of oxygen meters.
The water sample is first treated with excess manganese(II) sulfate solution and then with an alkaline solution of potassium iodide. The Mn(OH)2 initially formed reacts with the dissolved oxygen. The amount of MnO(OH)2 formed is determined by reaction with iodide ion in acidic solution. The iodine formed may be titrated against standard thiosulfate solution, using starch as an indicator.
Generalic, Eni. "Indicator." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
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