Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: jennielynn_1980 on June 27, 2006, 03:22:23 PM
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Hi all. I am reviewing the activity series and I am wondering if I am understanding it correctly.
The question I have to answer is if a reaction will occur in the following situations.
a) chromium dipped into silver nitrate
I said yes.
b) gold immersed in hydrochloric acid
I said no
c) nickel pellets dipped into bath of calcium acetate
I said yes
d) aluminum dropped into bath of sulphuric acid
I said yes
e) zinc dipped into lead (II) nitrate
I said yes
Now what I am unsure of is if it matter which order the elements come in. For example if you have a reaction with zinc and lead do they always react no matter what or does it depend which element comes first in the equation?
Thanks :)
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Show us how you got your answers.... :P
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There is a chart in my text book listing the elements in order of their reactivity and explaining the properties associated with each group. So I compared the first element with the second in the equation. For the first one Cr comes in the category that is active with acids and steam and silver comes in the category that has no reaction with non-oxidizing acids. Since the Cr comes higher up than the silver it kicks the silver out and replaces it. I know that is kind of a simplified explaination but that is basically how I concluded that their would be a reaction in the first instance.
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Ever seen a Standard Reduction Potential table?
http://www.science.uwaterloo.ca/~cchieh/cact//tools/rdvolt.html
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The general rule of thumb is that the more reactive metal will displace the less reactive metal.
Eg. Fe is more reactive than Ag, so Fe will displace Ag, ie.
Fe + 2AgNO3 => Fe(NO3)2 + 2Ag+
Hydrogen is being regarded as a "metal" in the reactivity series. So any metals positioned higher than hydrogen in the reactivity series will react with the hydrogen ions in acidic solution to produce hydrogen gas. For instance,
2Ag + 2HNO3 -> 2AgNO3 + H2
does not happen, because Ag is below H
Fe + 2HNO3 -> Fe(NO3)2 + H2
occurs spontaneously
The reactivity series can be derived from the Standard Reduction Potential Table.
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I get the metal replacement thing. I understand why this happens. The only thing I think I am unclear of is if the order of the elements/compound in the equation matter. It does right? Because in the first example if it was silver dipped into chromium nitrate (I don't even know if there is a chromium nitrate but just as an example) then there would be no reaction right because silver is not as reactive as chromium and therefore would not replace the chromium ions. I hope that makes sense. :-\
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I get the metal replacement thing. I understand why this happens. The only thing I think I am unclear of is if the order of the elements/compound in the equation matter. It does right? Because in the first example if it was silver dipped into chromium nitrate (I don't even know if there is a chromium nitrate but just as an example) then there would be no reaction right because silver is not as reactive as chromium and therefore would not replace the chromium ions. I hope that makes sense. :-\
Right, you have to identify the oxidizing agent (the one gaining electrons) and the reducing agent (the one losing electrons).
Using geodome's example:
Fe + 2AgNO3 => Fe(NO3)2 + 2Ag
Iron metal has an initial charge of 0, but becomes Fe2+ (thus losing two electrons). It is the reducing agent.
Silver begins as Ag+ ion in solution, becomes Ag metal with neutral charge (thus gaining 1 electron). It is the oxidizing agent.
What you have in your activity series is the "relative strengths" of oxidizing agents. Ag is "higher" than Fe in the activity series, which means it is a stronger oxidizing agent, which means it can take electrons away from Fe. And it does, since it goes from Ag+ + e- --> Ag(s), and Iron goes from Fe -> Fe2+ + e-
Just to add RE: The Order... If the rxn was instead Ag + Fe(NO3)2 => NR, there would be no rxn because the oxidizing agent Fe2+ is "lower" than Ag on the chart and so is not strong enough to pull electrons away, therefore NR.
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The only thing I think I am unclear of is if the order of the elements/compound in the equation matter.
Order in the equation doesn't matter, all that matters is reactivity series.
Cu(s) + 2Ag+ -> Cu2+ + 2Ag(s)
as well as
2Ag+ + Cu(s) -> Cu2+ + 2Ag(s)
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Thank you everyone. I understand now. :)