Re: Barium diphenylamine sulphonate Reaction

Don Wilkins wrote:

> On Thu, 13 Nov 2003 12:54:35 +1000, "bryan"
> <[EMAIL PROTECTED]> wrote:
> 
>>,;Hi all,
>>,;I am having a dispute with colleagues about FeO titrations .... Can 
anyone help
>>on this?
> 
> In the presence of HCl or H2SO4 the color change is not sharp and
> occurs early because of the oxidation of the indicator by dichromate.
> 
> Phosphoric acid is added to lower the oxidation potential of the
> ferrous/ferric oxidation system by forming a complex with Fe+3.
> (Fluoride also will do this but is not used for that purpose very
> often).
> 
> Unless you are measuring very small amounts of iron a blank would not
> be necessary but yes if you are going to determine a blank you better
> add the Fe+2 and H3P04 to each.
> 
> Kolthoff (U of Minnesota) or Willard (Michigan) discuss this in books
> or publications.

Thanks very much Don for the confirmation and background reasoning.Apologies 
for the delay. 
Bryan