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Reaction of NaOH with Chromic Acid

Reaction of NaOH with Chromic Acid

Reaction of NaOH with Chromic Acid

(OP)
I want to know how dilute solution of NaOH reacts with ppm levels of Chromic Acid. I would guess its a straight acid base reaction. Am I right?
 

RE: Reaction of NaOH with Chromic Acid

In dilute aqueous solution, at neutral and alkaline pH, chromic acid is present as the yellow chromate ion, CrO4-2.  The neutralization may be written

   H2CrO4 +2 NaOH = Na2CrO4 + 2 H2O

If your initial solution is acidic, you will observe a color change upon neutralization, as the orange-red dichromate ion Cr2O7-2 reacts to form yellow chromate:

   Cr2O7-2 + OH- = 2 CrO4-2 + H+

The neutralization reaction for an initially mildly acidic solution* is therefore

   H2Cr2O7 +4 NaOH = 2 Na2CrO4 + 3 H2O

Both sodium chromate Na2CrO4 and sodium dichromate Na2Cr2O7 (which can be formed at strongly acidic pH*) are highly soluble.  For removal of hexavalent Cr as part of a wastewater treatment process, it is best to either remove it via ion exchange or reduce it to trivalent Cr prior to neutralization.


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