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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: entice on November 29, 2009, 02:01:20 AM

Title: Oxidizing and Reducing Questions
Post by: entice on November 29, 2009, 02:01:20 AM

What is the oxidizing agent in the following chemical reactions
1. 2MnO₄^- + 5H₂SO₃ -> 2Mn²⁺ + 5SO₄^2- + 4H⁺ + 3H₂O  
2. 5S + 6KNO₃ + 2CaCO₃ -> 3K₂SO₄ + 2CaSO₄ + CO₂ +3N₂

What is the reducing agent in the following chemical reaction
1. 5Fe²⁺(aq) + MnO₄^-(aq) + 8H⁺(aq) -> 5Fe³⁺(aq) + Mn²⁺(aq) + 4H₂O(l)

What element is oxidized in the following chemical reaction
1. NiO₂ + Cd + 2H₂O -> Ni(OH)₂ + Cd(OH)₂

An explanation would be greatly appreciated. Thanks

Title: Re: Oxidizing and Reducing Questions
Post by: pear on November 29, 2009, 02:59:58 AM

Redox reactions are fun; just remember LEO GER (loss electrons oxidation, gain electrons reduction) and that reducing agents are oxidized and oxidizing agents are reduced.  Whichever element gains electrons [charge becomes less positive or more negative] is oxidized, making it the reducing agent.

Looking at the charge on Mn in #1:
MnO₄^-  :rarrow: Mn²⁺
Since the overall charge on the reactant-side molecule is -1 and O is always -2,   Mn + (4 x -2) = -1     Mn would have to be +7
Mn⁷⁺  :rarrow: Mn²⁺
To balance the charge, Mn⁷⁺ + 5e^- :rarrow: Mn²⁺
Mn is gaining electrons; remember "GER."  And if reduction is occurring, MnO₄^- in this equation is the oxidizing agent.


Hopefully that helps!

Title: Re: Oxidizing and Reducing Questions
Post by: entice on November 29, 2009, 05:30:34 AM

Thanks pear, that helped a lot!

Can you correct me if I'm wrong for the following..
What is the oxidizing agent in the following chemical reactions
2. 5S + 6KNO3 + 2CaCO3 -> 3K2SO4 + 2CaSO4 + CO2 +3N2
KNO3 is the oxidizing agent

What is the reducing agent in the following chemical reaction
1. 5Fe2+(aq) + MnO4-(aq) + 8H+(aq) -> 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)
H+ is the reducing agent

What element is oxidized in the following chemical reaction
1. NiO2 + Cd + 2H2O -> Ni(OH)2 + Cd(OH)2
Is not a redox reaction

Title: Re: Oxidizing and Reducing Questions
Post by: Borek on November 29, 2009, 07:11:44 AM

Quote from: entice on November 29, 2009, 05:30:34 AM

KNO3 is the oxidizing agent

Unfortunately, that's the only correct answer so far.

Title: Re: Oxidizing and Reducing Questions
Post by: entice on November 29, 2009, 06:44:57 PM

What is the reducing agent in the following chemical reaction
1. 5Fe2+(aq) + MnO4-(aq) + 8H+(aq) -> 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)
Fe2+
+2 -> +3

What element is oxidized in the following chemical reaction
1. NiO2 + Cd + 2H2O -> Ni(OH)2 + Cd(OH)2
Cd
0 -> +2

I should be right this time?

Title: Re: Oxidizing and Reducing Questions
Post by: Borek on November 29, 2009, 06:53:04 PM

Looks OK this time.

Title: Re: Oxidizing and Reducing Questions
Post by: pear on November 29, 2009, 10:28:43 PM

Yay!  Go through the steps and it's easy as pie.  I had a terrible time learning how to recognize them until someone told me to do the individual steps.  DO IT!