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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: badgirllili on March 31, 2015, 02:44:05 AM

Title: Titration
Post by: badgirllili on March 31, 2015, 02:44:05 AM

Hi. Thanks for viewing my post. :) Please help me answer this problem:

A 0.200 g sample of pyrolusite is analyzed for manganese content as follows: Add 50 mL of a 0.100 M solution of ferrous ammonium sulfate to reduce the MnO2 to Mn^2+. After reduction is complete, the excess ferrous ion is titrated in acid solution with 0.0200 M KMnO4, requiring 15.0 mL. Calculate the percent manganese in the sample as Mn3O4.

The reaction bet. Fe^2+ and MnO4^- is:
5Fe^2+ + MnO4^- + 8H^+ -> 5Fe^3+ + Mn^2+ + 4H2O

The reaction bet. Fe^2+ and MnO2 is:
2Fe^2+ + MnO2 + 4H^+ -> 2Fe^3+ + Mn^2+ + 2H2O

Title: Re: Titration
Post by: Borek on March 31, 2015, 03:34:11 AM

OK so far.

Hint: this is a back titration.

Title: Re: Titration
Post by: badgirllili on March 31, 2015, 04:42:47 AM

Quote from: Borek on March 31, 2015, 03:34:11 AM

OK so far.

Hint: this is a back titration.

My answer is 66.74%. Did I do it right? Thanks!

Title: Re: Titration
Post by: Borek on March 31, 2015, 08:09:51 AM

Looks OK.