Calculating Yield and Concentrations in a Precipitation Reaction

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Discussion Overview

The discussion revolves around a precipitation reaction involving sodium fluoride and calcium nitrate, focusing on calculations related to yield, concentrations of ions, and the interpretation of results from a specific problem set. Participants explore theoretical yield, percentage yield, and final ion concentrations in the solution.

Discussion Character

  • Homework-related
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the calculation of the concentration of Ca2+ ions remaining in solution, noting a discrepancy between their calculation (0.294 M) and the textbook answer (0.268 M).
  • Another participant expresses confusion regarding the concept of full dissociation and its relevance to the problem.
  • A participant critiques the question's formulation, suggesting that it lacks clarity and that the calculations might be based on assumptions that are not explicitly stated.
  • Some participants propose that the problem requires assuming full dissociation to arrive at the textbook answer, while others challenge this assumption.
  • There is a shared sentiment among participants that the question is poorly constructed, particularly regarding the use of the mass of precipitate (0.225 g) in the calculations.

Areas of Agreement / Disagreement

Participants generally express disagreement regarding the clarity and correctness of the problem, with multiple competing views on how to approach the calculations and the assumptions involved.

Contextual Notes

Participants note potential limitations in the problem's assumptions, particularly regarding full dissociation and the relationship between theoretical and actual yields. There is also uncertainty about how to correctly apply the solubility product in this context.

alingy1
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17. (20 marks) A 0.410g sample of sodium fluoride is dissolved in 25.00mL of water and is then reacted with 50.00mL of 0.500mol/L calcium nitrate solution. After the mixture is filtered, 0.225g of precipitate is recovered.
a ) Write the net ionic equation for the reaction which occurs.
b) Calculate the maximum mass of precipitate that could be formed (theoretical
yield).
c) Calculate the percentage yield for this reaction.
d) Calculate the concentrations of the three major ions in the final solution.


https://ca.answers.yahoo.com/question/index?qid=20111210111858AA1ObOY
For d) This website says :Mol Ca2+ remaining in solution: 0.025 mol Ca2+ initially - 4.88X10^-3 mol CaF2 formed = 0.0201 mol Ca2+ remaining / 0.075 L = 0.268 M Ca2+

My textbook answer says the same thing.

BUT WHY! That is the result of theoretical maximum yield 100%... I get 0.294M using 0.225g.
Can you back me up?
 
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I feel dumb :S It looks really simple but I don't get that 0.268M! Why are they talking about full dissociation?!
 
It is a rather lousy question IMHO. I have no idea what is the "correct" answer here. That is, concentrations can be calculated from the solubility product, but that's an entirely different problem then.
 
I think they waant to us to keep up with the 0.255g.. But apparently we are supposed to assume full dissociation!
 
I agree. Bad formulation. And even their answer does not make sense since they ask for 0.225g dissociation.
 

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