The end point of a potassium dichromate(VI) titration isn't as easy to see as the end point of a potassium manganate(VII) one. However, the color is made difficult by the strong green also present. This gives a violet-blue color in the presence of excess potassium dichromate(VI) solution. There are several such indicators - such as diphenylamine sulfonate. ![]() These change color in the presence of an oxidising agent. With potassium dichromate(VI) solution you have to use a separate indicator, known as a redox indicator. Unfortunately potassium dichromate(VI) solution turns green as you run it into the reaction, and there is no way you could possibly detect the color change when you have one drop of excess orange solution in a strongly colored green solution. As soon as you add as much as one drop too much, the solution becomes pink - and you know you have reached the end point. As you run the potassium manganate(VII) solution into the reaction, the solution becomes colorless. 243361 Chromium (III) potassium sulfate dodecahydrate Write a review Ask a question ACS reagent, 98 Synonym (s): Chrome alum, Potassium chromium (III) sulfate dodecahydrate Linear Formula: CrK (SO4)2 12H2O CAS Number: Molecular Weight: 499.40 EC Number: 233-401-6 MDL number: MFCD00149917 PubChem Substance ID: 329752454 NACRES: NB. Potassium manganate(VII) titrations are self-indicating. The main disadvantage lies in the color change.That means that you don't get unwanted side reactions with the potassium dichromate(VI) soution. Potassium manganate(VII) oxidises chloride ions to chlorine potassium dichromate(VI) isn't quite a strong enough oxidising agent to do this. Potassium dichromate(VI) can be used in the presence of chloride ions (as long as the chloride ions aren't present in very high concentration).That isn't true of potassium manganate(VII). ![]() That means that it can be made up to give a stable solution of accurately known concentration.
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