Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: kaylaalicia on March 19, 2009, 11:17:28 PM
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This question should be quite simple. Yet I am getting it wrong. It it's really frustrating. Can someone see what i'm doing wrong? Or maybe it's because my concepts are messed up. ???
Assuming standard conditions, and considering the table of standard reduction potentials for half-reactions, given in your text, rank the following species according to their relative strength as reducing agents. For example, the most powerful reducing agent would be given rank "1", and the least "6".
Cd
I-
Fe2+
Zn
F-
K
A link for a Standard reduction potential table is here: http://www.jesuitnola.org/upload/clark/refs/red_pot.htm
The order I got was 4,3,2,5,1,6 ( F-, Fe2+, I-, Cd, Zn, K)
Reasoning is that the reducing agent is oxidized and therefore loses the electrons. So looking at the standard reduction potential table, I got my voltage values from there, and changed the signs where I needed to. But i keep getting it wrong. Help and a push in the right direction would be fantastic. =]
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Think about it. A good reducing agent wants to lose an electron (be oxidized) what type of elements just love to lose electrons?
Why would a fluorine ion, the best at electron gathering, want to lose an electron?
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Darn it. I'm still confused.
So writing out the half reactions and their corresponding voltages,
Cd: Cd :rarrow: Cd2+ +2e- +0.403V
I-: 2I- :rarrow: I2+ 2e- -0.536V
Fe2+: Fe2+ :rarrow: Fe3++e- -0.771V
Zn: Zn :rarrow: Zn2++e- +0.763
F-: 2F- :rarrow: F2 + 2e- -2.87
K: K :rarrow: K++e- +2.925
Now, don't you just order them? With positive to negative to get the order of strength of reducing agents?
From what i've just done, it would be:
K, Zn, Cd, I-, Fe2+, F-
Is this right? ???
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Darn it. I'm still confused.
So writing out the half reactions and their corresponding voltages,
Cd: Cd :rarrow: Cd2+ +2e- +0.403V
I-: 2I- :rarrow: I2+ 2e- -0.536V
Fe2+: Fe2+ :rarrow: Fe3++e- -0.771V
Zn: Zn :rarrow: Zn2++e- +0.763
F-: 2F- :rarrow: F2 + 2e- -2.87
K: K :rarrow: K++e- +2.925
Now, don't you just order them? With positive to negative to get the order of strength of reducing agents?
From what i've just done, it would be:
K, Zn, Cd, I-, Fe2+, F-
Is this right? ???
That looks better.
On a list of standard reduction potentials the more negative a number the better a reducing agent it is. So when you flip the negative sign around you receive a list of oxidation potentials. So the elements that want to be oxidized are more positive and the elements who hate to be oxidized are negative.
Potassium and the Akali family of metals are amazing reducing agents because they want to give up that single electron on their outer shell. They are so good that they can't even be kept in air because they oxidize so easily. Zinc and Cadmium are of reasonable strength. The ions on the list are either very strong electron gathers or metals that have already given up several electrons. Thus it makes sense that those would not be good reducing agents since they will be very reluctant to give up any more electrons.
So bottom line is that list goods correct.
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Yay! Thank you so much for your help :D It has really helped my understanding of this topic.