How to know products if given reactants

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Glenda Marshall DIS 3M
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How to know products if given reactants

Postby Glenda Marshall DIS 3M » Tue Mar 10, 2015 9:40 pm

Homework problem #13.17 asks us to

"write the balanced half-reactions for the redox reaction of an acidified solution of potassium permanganate and iron (II) chloride."

How would you know how to write the half reactions when they only give you the reactants? Thanks!

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Re: How to know products if given reactants

Postby martha-1I » Wed Mar 11, 2015 12:40 am

They gave us potassium permanganate and iron (II) chloride, so I broke those apart into their own half reaction and double checked that my reactions were correct by checking appendix 2A to see if my reactions matched the ones for these molecules.
The following are the unbalanced half redox reactions:
MnO4- ---> Mn2+
Fe2+ ---> Fe3+

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Re: How to know products if given reactants

Postby Chem_Mod » Wed Mar 11, 2015 1:10 am

You have potassium permanganate (KMnO4) and iron(II)chloride (FeCl2). Potassium and chlorine are spectator ions and thus do not take react. Therefore, we only worry about the MnO4- and the Fe+2.

The half reactions for MnO4- and the Fe+2 in an acidic medium are:
MnO4- + 8H+ +5e- Mn+2 + 4H2O
Fe Fe+2 + 2e-

You need to then balance the mole electrons so you multiply the first equation by 2 and the second equation by 5 to get...
2MnO4- + 16H+ +10e- 2Mn+2 + 8H2O
5Fe 5Fe+2 + 10e-

The overall reaction becomes...
2MnO4- + 16H+ +5Fe 2Mn+2 + 8H2O + 5Fe+2

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