Rates of reaction - kinetics (A2)

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I'm doing my coursework on the amount of manganese in tea and I am having trouble with creating a redox reaction and overall reaction between manganese and the oxidising agent ammonium peroxodisulphate. Everytime I try to create the overall reaction, the charges dont balance. 130408

Ulex writes
 
I do not know this reaction, but I am assuming that the peroxodisulphate ion is reduced to sulphate and that the manganese in tea is in the form of Mn²⁺ which is oxidised to MnO₄^-. This is certainly possible theoretically but, as I say, I’ve never tried it. In a sense it doesn’t matter, it’s the general method you are after; you could apply it in other situations.
 
The equations are:
 
S₂O₈^2- + 2e^- -> 2SO₄^2-
Mn²⁺ + 4H₂O -> MnO₄^- + 8H⁺ + 5e^-
 
Multiply the first equation by 5 and the second by 2 to make the numbers of electrons equal.
 
5S₂O₈^2- + 10e^- -> 10SO₄^2-
2Mn²⁺ + 8H₂O -> 2MnO₄^- + 16H⁺ + 10e^-
 
Then add the two equations together:
 
5S₂O₈^2- + 10e^- + 2Mn²⁺ + 8H₂O -> 10SO₄^2- + 2MnO₄^- + 16H⁺ + 10e^-
 
Cancel the electrons and you have the overall equation:
 
5S₂O₈^2- + 2Mn²⁺ + 8H₂O -> 10SO₄^2- + 2MnO₄^- + 16H⁺
 

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updated: 13 April 2008