Hello, it looks like this lab covers a lot of chemistry topics, but mainly oxidation and reduction, and reaction rate. Here are the expected oxidation and reduction reactions that are occurring:
Oxidation 5 Fe (s) ––�?gt; 5 Fe3+ (aq) + 15 e�?/SUP>
Half-Rxn
Reduction 3 MnO4�?/SUP> (aq) + 15 e�?/SUP> + 24 H+ (aq) ––�?gt; 3 Mn2+ (aq) + 12 H2O (l)
Half-Rxn
Overall 5 Fe (s) + 3 MnO4�?/SUP> (aq) + 24 H+ (aq) ––�?gt; 5 Fe3+ (aq) + 3 Mn2+ (aq) + 12 H2O (l)
Net-Ionic
Reaction
Iron metal becomes oxidized to the yellow Fe3+ ion ultimately, while the MnO4�?/SUP> ion is reduced to the nearly colorless Mn2+ ion. But if excess iron metal is present, the situation can be a little more complicated, because the iron metal can reduce Fe3+ ion:
Fe (s) + 2 Fe3+ (aq) ––�?gt; 3 Fe2+ (aq)
Fe2+ ion is nearly colorless in dilute solution, so in the presence of excess iron wire, you may not see the yellow color of Fe3+ ion. But if you observe a yellow color appearing in the reaction, you know that you are forming Fe3+ ion. I'm not certain about this without observing the reaction, so for now I'll assume the reaction forming Fe3+ is correct.
We can include the sulfate spectator ions:
5 Fe (s) + 3 KMnO4 (aq) + 12 H2SO4 (aq) ––�?gt; 5/2 Fe2(SO4)3 (aq) + 3 MnSO4 (aq) + 3/2 K2SO4 (aq) + 12 H2O (l)
If we multiply through by 2, we will have all whole number coefficients:
10 Fe (s) + 6 KMnO4 (aq) + 24 H2SO4 (aq) ––�?gt; 5 Fe2(SO4)3 (aq) + 6 MnSO4 (aq) + 3 K2SO4 (aq) + 24 H2O (l)
You observed that the rate of the reaction is greater if more iron wires are in contact with the solution. Since the rate of reaction of solid reactants depends on their surface area, I would expect this to be the reason. Five wires have a greater iron surface area than four wires, etc.
Steve
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