Tungsten Blue Reducing Potassium Dichromate
In the reaction of potassium dichromate and tungsten blue, tungsten blue (blue tungsten oxide,WO2.9）as indicator in new Potassium Dichromate Method measuring iron content intuitively reflect reaction ending to calculate iron content.
Potassium dichromate, formula of K2Cr2O7, is a strong oxidant with highly toxic and carcinogenic, an orange-red solid at room temperature. It is classified by IARC as Group I carcinogens, and as the strong oxidant, has very wide range of application in the laboratory and industry.
The new Potassium Dichromate method (Titanium Trichloride - Potassium Dichromate Method) is removing the highly toxic of mercuric chloride on the basis of mercury measuring iron.
The process reflects in that firstly using SnCl2 to reduce most of Fe3+ until the solution turns from red-brown to pale yellow after ore sample was dissolved, then takes sodium tungstate as indicator and follow using TiCl3 to continue continue reduce the excess Fe3+ to Fe2+; after the quantitative Fe3+ turns to Fe2+, the excessive one drop of TiCl3can reduce the hexavalent tungsten of indicator to pentavalent tungsten compound which is tungsten blue, solution appears in blue at this time; then potassium dichromate solution is dropped until tungsten blue just fade.
The reaction of phosphotungstic acid reduced to tungsten blue can be expressed as:
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