Redox reactions?

Question

I did a lab the other day and part of it was to find out if a reaction took place. One in particular was:
Zn(NO3)2+Cu-->Cu(NO3)2+Zn

The only reason I knew nothing had happened in this reaction (besides the teacher tellin me) is that the final solution was not blue. (I think that means that the Cu did not dissolve into a solution with NO3?)

Anyway, our homework for this lab has asked the question:

Will the following reaction occur?

Fe(NO3)2(aq) + Cu(s) -> Cu(NO3)2(aq) + Fe(s)

I am a little confused as to what he could be asking. Does this mean anything to anyone? Again, we are working with Redox.

Thanks for your help.
Linda

The half reactions for Fe are:
Fe--->Fe 2+ +2e-

and for Cu:

Cu-----> Cu 2+ +2e-

Do I add the electrons? And if that is positive then the reaction occures? Im confused.

Wouldnt Fe be reduced, therefore be the oxidizing agent? And Cu oxidized and Cu be the reducing agent? I think Pero1 is wrong..?? (Maybe). Anyway, still does not answer my question. How can I tell if a reaction actually took place? If you look at my first example, you can also get a reducing and oxidizing agent, but no reaction actually took place. See what I mean?

Answer 1

Karen R has given you the answer but maybe you need it in more detail:

In order to see if a redox reaction is going to happen, you have to add the half reactions and their potentials and if the potential that you get for the whole reaction is positive then it will happen (spontaneously). Let's do that for your example:

The first thing to do is to find the standard potentials from a table (in your textbook, on the net, etc). Usually you will find them as reduction potentials, meaning that in the table you will see the potential for reduction half reactions.

Fe(+2) + 2e -> Fe(0) with E01=-0.447 Volt (1)
Cu(+2) + 2e -> Cu(0) with E02= +0.342 Volt

However you need to see the half reaction for oxidation of Cu, so you just inverse the reaction and change the sign of the potential
so
Cu(0) -> Cu(+2) +2e with E'02=-0.342 Volt (2)
add half-reactions (1) and (2) and you get

Fe(+2) + Cu(0) -> Fe(0) + Cu(+2)
with E=E01+E'02= (-0.447)+ (-0.342)= -0.789 Volt <0 therefore it doesn't take place

The reverse reaction would have E=+0.789 and would take place. So if you had a blue solution of Cu(NO3)2 (it is blue because of the Cu+2) and added iron fillings you should see it lose its colour

Answer 2

to verify that a redox reaction to take place, 2 factors ought to replace electrons and show diverse oxidation numbers A. in simple terms finding at it I see that no element replaced oxidation selection so it is not a redox reaction NON REDOX B. here I see that Li is going from a Li+a million to a Li 0 mutually as Na is going from an Na 0 to an Na+a million. Electrons are exchanged. this could be a redox reaction REDOX

Answer 3

No pun intended, I am rusty on this myself, and have to look in my daughters high school chemistry text:

Iron is already in the oxidized state, so it is the oxidizing agent, since if we were to believe the reaction it is suppose to get electrons and thus become reduced.

You need a list of reduction potentials.

Cell Potential = {reduction potential of half cell where reduction occurs} minus {reduction potential of half cell where oxidation occurs}

So we want to know if Iron++ can be reduced by Copper to Fe, and Cu can be oxidized by Iron++ to Cu++

{reduction pot. where reduction occurs on Fe++ to Fe} = -0.44
{reduction pot. where oxidation of Cu to Cu++ } = 0.52

the difference sums to -0.96, so it does not seem likely.

Note: the subtraction of the reduction potential when we consider it as an oxidation reaction is because its the reverse reaction.

Everything listing these half cell reactions voltages are in relation to the hydrogen/H+ half cell. Thus when we see that
(Zinc++) + 2 e- -------------> Zn has a -0.76 V, we have to think of seeing zinc bubbling away in dilute HCL as a reminder that H+ will oxidize Zn and form H2 gas rather than H2 will reduce Zn++ to Zn

Answer 4

i just did a simple oxidation number check and found out this
+2 -2 0 +2 -2 0
Fe (NO3)2 Cu CU (NO3)2 fe
So.. answer of Redox reaction known as Oxidation- reduction reaction.

Reduction:Fe(+2,0) Reduction agent:Fe(NO3)2
Oxidation:Cu(0,+2) Oxidation agent:Cu

gl with ur ap chem

Answer 5

you have to separate them into half reactions. Each half reaction should have a potential value associated with it. Add up the two half reactions and if the end result is positive the reaction will occur.

there should be a table of half reactions in your textbook in the electrochemistry section. Also remember to switch the sign if the reaction is going the other way.

good luck