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Oxidation Reduction Reactions

  1. May 1, 2007 #1
    Ok I'm trying to do my chemistry homework and well i'm stuck. I have the first few questions done i'm stuck on question 5 step 3, an i'm not sure the other are correct. I still have no idea how to balance equations and well here we go again with balanceing things...

    1. What is the difference between an oxidizing agent and a reducing agent?
    Reduction means what it says: the oxidation number is reduced in reduction. Oxidation is the reverse process: the oxidation number of an atom is increased during oxidation.
    2. When first learning to balance equations, we learned that the number of atoms of each element in the products and reactants must be equivalent. What are some additional factors that must be taken into account when balancing equations for redox reactions?

    Combine the half reactions to eliminate the electrons from the overall reaction.

    3. What are half reactions?
    A half-reaction is simply one which shows either reduction OR oxidation, but not both.

    4. What two aspects of the half-reaction equations must be balanced?
    atoms and charge in order

    5. For the equation Ag + NO3 - à Ag + + NO
    (Note: This reaction takes place in an acidic solution.)

    Step 1: What substance is reduced?
    Oxygen
    Step 2: What substance is oxidized?
    Silver
    Step 3: What is the half reaction for oxidation?

    Step 4: What is the half reaction for reduction?

    Step 5: What is the net balanced equation?

    Step 6: What is the reduced equation?
     
  2. jcsd
  3. May 1, 2007 #2

    chemisttree

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    This looks like silver metal is being oxidized to Ag+. The oxidizing species is nitrate (acidic). Can you write a half reaction for what happens to silver?
     
  4. May 1, 2007 #3
    ag-->ag+ ?? I'm not sure if thats what you mean but what happens to silver is it is oxidized ag-->ag+...? correct?
     
  5. May 2, 2007 #4

    chemisttree

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    Where did the electron go? Show everything. Example

    Fe -----> Fe+2 + 2e- (Half reaction)

    You must account for the nitrate half reaction as well. A good place to start is to write down an equation that is balanced.
     
  6. May 2, 2007 #5
    You mean like this?
    Ag---->Ag+ 2g-
    and
    NO3---->NO+O3
     
  7. May 2, 2007 #6
    Red. agents are always oxidised
    Oxi. agents are always reduced...right

    since metals are e- donors....they are reducing agents!!! here Ag is the reducing agent. oxidation state(OS) of Ag is 0....that of Ag+ is +1..... this confirms oxidation of Ag, i.e oxidation state has increased.

    NO3- acts as an oxidising agent.... OS of N in NO3- is +5 and that in NO is +2
    there has been a decrease in oxidation number.... this confirms reduction of NO3- to NO, i.e. OS of Nitrogen has decreased

    oxidation... Ag -------> Ag+ + e-

    reduction NO3- + e- ------> NO

    wait a sec..... are you sure of the above eqn???? the half eqn for oxidising eqn is ok....but for the reducing one..... can't find out...sry


    the NO3- is supposed to accept e-,,, but NO cannot be formed..... well i'm not sure
     
  8. May 2, 2007 #7
    No i'm not sure of anything at this point all i know is what my teacher told me. Thats why i'm hopeing someone can help me and my chemically challenged self....
    For the equation Ag + NO3 - à Ag + + NO
    (Note: This reaction takes place in an acidic solution.)

    Step 1: What substance is reduced?

    Step 2: What substance is oxidized?

    Step 3: What is the half reaction for oxidation?

    Step 4: What is the half reaction for reduction?

    Step 5: What is the net balanced equation?

    Step 6: What is the reduced equation?
     
  9. May 2, 2007 #8

    chemisttree

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    Did you just misspell 'e-'?

    Balance the nitrate reaction so that there are as many oxygens on the left as the right. Show charges! NO3 is not correct. It's NO3-. You MUST account for all of these charges to even begin to answer this question correctly.

    Check your work carefully!
     
    Last edited: May 2, 2007
  10. May 2, 2007 #9
    Ag---->Ag+2e-
    and
    NO3- ----> NO+3e-

    ???
     
  11. May 2, 2007 #10

    chemisttree

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    refer to post #8.
     
  12. May 3, 2007 #11

    chemisttree

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    NO3- has nitrogen in the +5 oxidation state. NO has the nitrogen in the +2 state. This is a 3 electron reduction of nitrogen. The electrons come from the silver metal. Silver is oxidized from a zero valency to a +1.

    Ag --------> Ag+ + 1e- (Ag oxidized, half reaction)

    NO3- + 3e- ---------> NO + 2O-2

    It was done in acidic solution and those two O-2's are just dying to be water molecules. Add some H+ to the nitrate half reaction to react with the O-2's.

    NO3- + 3e- + 4H+ --------> NO + 2H2O (NO3- reduced, half reaction)

    Multiply the silver half reaction by three to account for the 3e-'s in the above reaction and you get:

    3Ag --------> 3Ag+ + 3e-

    combining the two reactions yields:

    3Ag + NO3- + 3e- + 4H+ ---------> 3Ag+ + 3e- + NO + 2H2O (net balanced equation)

    Canceling the 3e-'s from both sides of the reaction yields:

    3Ag + NO3- + 4H+ -----------> 3Ag+ + NO + 2H2O (reduced equation)
     
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