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Overcoming interference from hydrolysable cations when titrating for free sulfuric acid
December 9, 2009
During atmospheric direct leaching of ZnS by using ferric iron in sulfuric acid medium. We should determine free acid of the sample solution. My problem is finding a solution to the ferric iron interference during the determination of sulfuric acid by titration.
The concentration of ferric iron is high and this causes interference in determining the acid concentration. This cation consumes a large part of the titrant during the conventional acid-base titration method.
I have to find a method that allows for the titration of sulfuric acid in the presence of ferric iron and other hydrolysable cations such that the titration results are indicative of acid content only. Does anyone know a practical solution in detail and plain English?
Student - UK
First of two simultaneous responses --
To titrate an acid solution that is loaded with a precipitate able metal you need to use a dilute caustic such as 0.1N NaOH [on
eBay or
Amazon]
added very slowly with intense agitation and a suitable indicator. If your diluted sample has intense color, you will need to use a pH meter. Titrate to a pH of around 3.5. Look at the curve for a strong acid/strong base titration and you will see that the amount of titrant used is nearly identical to that of a pH of 7.0 The above avoids the precipitation of the metal in any significant quantity.
I assume that you are diluting your sample with DI water to 50 or 100 mL.
- Navarre, Florida
December 11, 2009
Second of two simultaneous responses -- December 11, 2009
Sir:
Your indicator must change color at a relatively low pH. Also you should dilute the sample to avoid the color of the Fe+3.
Regards,
Galvanizing Consultant - Hot Springs, South Dakota, USA
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