Calculating EDTA Titration Volume for CoSO4 Solution

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Discussion Overview

The discussion revolves around calculating the volume of EDTA required to titrate a cobalt(II) sulfate (CoSO4) solution. Participants explore the stoichiometry of the titration, the role of EDTA as a chelator, and the necessary calculations involved in determining the moles of CoSO4 and the corresponding volume of EDTA needed for the titration.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • One participant presents a calculation attempt for the moles of CoSO4 and expresses uncertainty about the use of equilibrium constants and the relationship between CoSO4 and EDTA.
  • Another participant suggests a method to calculate the required volume of EDTA by determining the moles of CoSO4 and using the molar ratio of EDTA to CoSO4.
  • Some participants propose that the titration may be a straightforward 1:1 mole ratio between EDTA and CoSO4, but caution that pH control might be necessary if certain factors are relevant.
  • There is a question about how to determine the molar ratio of EDTA to different metal ions, with reference to examples provided in the textbook.
  • A participant notes that the assumption of a 1:1 mole ratio is common, emphasizing that EDTA acts as a chelator, coordinating with one metal ion per molecule.

Areas of Agreement / Disagreement

Participants express uncertainty about the exact stoichiometry of the titration and the role of pH, indicating that there is no consensus on these points. Some agree on the 1:1 ratio for EDTA and CoSO4, while others seek clarification on how this ratio is determined for different metal ions.

Contextual Notes

Participants highlight limitations in the textbook's explanations regarding the molar ratios and the importance of equilibrium constants, which may affect the calculations. There are unresolved questions about the role of pH in the titration process.

LakeMountD
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Homework Statement


A solution contains 1.694mg of CoSO4 (155.0 g/mol) per mL. Calculate the volume of 0.08640 M EDTA needed to titrate a 25 mL aliquot of this solution.


Homework Equations


Not really sure, the book is no help but this may help:

K(CoSO4) = [CoSO4] / ([CO2+] [SO42-])
K'CoSO4 = alpha4 * KCoSO4

The Attempt at a Solution



My book is absolutely horrible which is why I had to come to the forums for help but I am assuming I find the mol. of CoSO4, which was 2.73 x 10^-4 then assume that [CoSO4] ~= 4.37x10^-4

I think you use K'CoSO4 = alpha4 * KCoSO4, but again I can't figure it out :(
 
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Okay I think I might have figured it out. Get moles of CoSO4, then multiply that by the molar ratio of EDTA to CoSO4 then multiply by the concentration of EDTA?
 
Superficially, best guess is that this should be a fairly uncomplicated 1 to 1 mole titration of the EDTA specie to the Co specie. If that "alpha" stuff is important in the exercise, then the superficial idea is not enough, and that some pH control might be needed. If you have the time, check an alternative quantitative book and ask your teacher.
 
symbolipoint said:
Superficially, best guess is that this should be a fairly uncomplicated 1 to 1 mole titration of the EDTA specie to the Co specie. If that "alpha" stuff is important in the exercise, then the superficial idea is not enough, and that some pH control might be needed. If you have the time, check an alternative quantitative book and ask your teacher.

Yeah that is the problem I am having. How do I know what the molar ratio of EDTA to any metal is? The book doesn't explain it in the examples, it just throws the ratio in there. It gives a 1:1 ratio to EDTA:Mg(NO2)2 but not sure about the others.

Thanks.
 
How do I know 1:1 ? Habit! Not remember exactly how. Just assume 1:1 mole ratio. The EDTA is not just a ligand; it is a CHELATOR. One EDTA will coordinate bond with one metal ion. (mole-wise, that is)
 

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