Why would limiting reactant not be necessary to determine?

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Discussion Overview

The discussion revolves around the necessity of determining the limiting reactant in a series of chemical reactions involving copper, specifically in the context of calculating final percent recovery from a lab experiment. The scope includes conceptual understanding and application of stoichiometry in chemical reactions.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why it is unnecessary to identify the limiting reactant, suggesting that if copper were in excess, the reaction would stop when the other reactant is used up, potentially affecting the amount of copper carried through the experiments.
  • Another participant speculates about the nature of the other reactants involved, mentioning electrons in the context of copper reduction.
  • There is a suggestion that in each reaction, the other reactant might be in excess or that there may be no other reactant at all.
  • A participant notes that for certain reactions, such as metathesis and thermal decomposition, it may not be necessary to calculate the limiting reactant, but raises concerns about the stoichiometry in other reactions.
  • One participant emphasizes that knowing the initial and final amounts is sufficient for calculating final percent recovery, questioning the relevance of intermediate steps.
  • A later reply reflects a change in perspective, suggesting that the question implies an assumption that copper is the limiting reagent, and proposes that the answer may be that copper is always limiting, allowing for maximum recovery through each reaction.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of determining the limiting reactant, with some suggesting it may not be needed while others question the implications of excess reactants. The discussion remains unresolved regarding the necessity of identifying limiting reactants in all cases.

Contextual Notes

Participants discuss various types of reactions and their implications for stoichiometry, but there are unresolved assumptions about the nature of reactants and the conditions under which limiting reactants may or may not be relevant.

Greywolfe1982
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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?
 
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What other reactant is there? Electrons?

Cu+2 + 2e- ------> Cus
 
I guess in each case other reactant was in excess? Or there was simply no other reactant?
 
chemisttree said:
What other reactant is there? Electrons?

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

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.
 
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?
 
Borek said:
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?
 

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