Question 40

[pinoalejan6739]

i dont understand this question at all!

[bearsfan544772]

If I'm reading the explanation correctly, we are looking for values that are less positive or more negative than than the reduction of Iron (III) to Iron (II). I count 3 ... at values of +1.00, +1.33, and -0.91

Why is the -0.91 value omitted?

[j5devries4378]

Since a positive Ecell represents spontaneous, and
Ecell= E(cath)-E(anode), must be positive. Since the reduction happens at the cathode, and we know the RedPotential is +.77V, you have
Ecell = (.77V) - E(anode) = positive.

Since the question asks for which ones could NOT reduce the Iron, you want a negative cell potential. I reversed the cell potentials for all of the reactions since they are being oxidized, instead of reduced like the table shows. (ie Zn -> Zn2+ + 2e). However, this gave me the opposite result of what I expected.

When I plug the values in, in the UNREVERSED way, as they are in the table, the question works out.

For example:
Ecell = (+.77V) - (+1.00) = -(.23). I just don't know why the values in the table would not be reversed.
Can anyone explain this?

[j5devries4378]

Actually, a more positive cell potential means they are more easily reduced (better oxidizing agent). Just look for the more positive cell potentials. That is the answer.

[DLBMCAT]

The above explanation still does not make any sense to me, can someone elaborate?

[serafin8506737]

redox reaction pair if Fe is being reduced something needs to get oxidized. Anyways to cut to the chase high positive values for E are spontaneous,high positive values also indicate that the product is a great OXIDIZING AGENT. Species with really negative values for E are non spontaneous, so their reactants are great REDUCING AGENTS. If you toy around with all the values and flip the signs so that the end product will be positive (spontaneous) you can see that 1.00 V and 1.33 when turned negative and added to .77 (which needs to be positive because its a reduction and thats what youre looking for) in the half reaction will always yield a negative value and thus make it non spontaneous and impossible to reduce

learned this in princeton review hope it helps