Why would limiting reactant not be necessary to determine?

[Greywolfe1982]

Homework Statement

I did a lab with a series of reactions involving copper, going from a copper nitrate solution to pure copper. One of the questions for the lab asks why it isn't necessary to determine the limiting reactant in each of the reactions to calculate final percent recovery.

The Attempt at a Solution

I really can't wrap my head around why it wouldn't be necessary to ensure that copper is the limiting reactant. If the copper was in excess, would the reaction not stop when the other reactant is used up, and you're left with some copper in form A and the remaining copper in form B, which would lower the amount of copper being carried through the experiments?

 

[chemisttree]

What other reactant is there? Electrons?

Cu⁺² + 2e^- ------> Cu_s

 

[Borek]

I guess in each case other reactant was in excess? Or there was simply no other reactant?

 

[Greywolfe1982]

What other reactant is there? Electrons?

Cu⁺² + 2e^- ------> Cu_s

Mostly metathesis reactions (Cu(NO3)2+2NaOH --> 2NaNO3+Cu(OH)2), one that was adding heat (Cu(OH)2 --> CuO+H20). The latter I could see there being no need to calculate the limiting reactant of course, but with the first equation it seems like you could still use a minimal amount of NaOH and not cause the copper to totally react.

 

[Borek]

Just a moment. You know initial amount, and you know final amount, isn't it? You are asked to calculate final percent recovery. Does it matter what happens in between?

 

[Greywolfe1982]

Just a moment. You know initial amount, and you know final amount, isn't it? You are asked to calculate final percent recovery. Does it matter what happens in between?

Hmm...this made me change my thinking about the question a bit. I'll read the question directly as it's worded in the lab:

Why is it not necessary to determine the limiting reactant in each of the steps in the series of reactions in order to calculate the final percent recovery?

After I read your post and reread the question, I'm thinking that I understand the question better now. It doesn't make the statement that limiting reactants aren't necessary to consider for any of the equations, but rather that we can assume the copper compound is the limiting reagent...I think. If so, then the answer would simply be because of the fact that the copper is always limiting, and the maximum amount of copper possible will be carried through each reaction. Does this seem like the right answer?