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Chemistry Question - Cr(VI)
Posted By: Wolfspirit, on host
Date: Tuesday, October 9, 2001, at 00:21:06

I have this procedure for the determination of chromium hexavalent, or Cr(VI), in aqueous effluent. The trouble is that it's from a kit from an analytical products manufacturer. The kit gives minimal information on the actual chemistry involved. I wonder if any of our Rinkydinks can help explain why this inorganic chemistry protocol works (or doesn't work):

1. Take liquid chromium sample and alkalinize it to pH 12.5 to 13 using a sodium hydroxide base.

2. Add 1-2% (w/w) of 35% peroxide H2O2.

3. Then boil the solution 10 minutes to remove all traces of H2O2. Allow solution to cool to room temperature.

4. Acidify sample solution to between pH 2 and 3 using sulfuric acid.

5. Pipette small samples of solution into colorimetric vials, filling one with just plain solution to act as a zero "blank," and the other vial with solution + a color-developing agent. After 10 minutes, measure the colour absorption using the colorimeter to check for chromium concentration.


1) What are the mechanics, or oxidation states, of the oxidation/reduction mechanisms that are being involved (targeted) by this metholodogy?

2) What is the Limits of Detection (the range of validity) of this method? I'm *presuming* that it is a colorimetric technique.

2) Is there a better (faster, cheaper) way of detecting Cr(VI) content?

Cheers and Thanks for the help.


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