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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: warnie on March 12, 2008, 08:15:49 AM

Title: Fe2+ and Fe3+ determination
Post by: warnie on March 12, 2008, 08:15:49 AM

In the experiment to determine Fe2+ and Fe3+ concentration in a solution using K2Cr2O7 Fe3+ is reduced
to Fe2+ using Zn dust and H2SO4. Why can't Zn dust be used alone? (N-Phenylanthranilicacid was used as indicator) 

Title: Re: Fe2+ and Fe3+ determination
Post by: AWK on March 12, 2008, 11:34:28 AM

Zn + H2SO4 = ZnSO4 + H2
Hydrogen is a reductor.

Title: Re: Fe2+ and Fe3+ determination
Post by: warnie on March 13, 2008, 08:18:21 AM

Thanks
But Zn can alone reduce Fe3+.

Title: Re: Fe2+ and Fe3+ determination
Post by: AWK on March 13, 2008, 08:37:43 AM

Without acid, Zn could eventually replace Fe2+ and Fe3+, but then metallic Fe will react with water to form Fe(OH)2. Using acid from Fe(OH)2 you can obtain FeSO4, hence it does not matter what mechanism of reduction is.