Solve Concentration Problem: K, Cr2O7, Equilibrium

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Discussion Overview

The discussion revolves around a homework problem related to the equilibrium concentrations of chromate and dichromate ions, specifically focusing on the interpretation of the problem statement and the application of the equilibrium constant expression.

Discussion Character

  • Homework-related
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses confusion regarding the wording of the problem, questioning whether the provided concentration refers to equilibrium concentrations or initial concentrations.
  • Another participant interprets the concentration of 0.100 M as the equilibrium concentration, not the initial concentration.
  • A participant clarifies their earlier statement about "mole-mole" ratios, indicating they meant mole-to-mole ratios in stoichiometry.
  • There is a query about the expression for the equilibrium constant and how stoichiometric coefficients should be applied in the context of the problem.
  • Some participants agree that the ambiguity in whether the values are equilibrium concentrations is a central issue, noting that such details are usually explicitly stated in problems.

Areas of Agreement / Disagreement

Participants generally agree that the main point of contention is whether the concentrations mentioned in the problem are equilibrium values or not. Multiple interpretations exist, and the discussion remains unresolved.

Contextual Notes

There is uncertainty regarding the assumptions made about the concentrations in the problem statement, particularly the lack of explicit mention of whether they are equilibrium or initial concentrations.

Euler2718
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Homework Statement



Question 9)

IMG_3193.JPG


Homework Equations



K=\frac{[P]}{[R]}

The Attempt at a Solution



What is confusing me is the wording. It merely says for the concentration of chromate. All this time we've been doing the equilibrium concentrations. Doing mole-mole with the Cr2O7 yields the answer to be D. I then assumed that it meant that they were the concentrations at equilibrium, which gave C to be the correct answer after preforming the equilibrium constant equation. Thanks for reading.
 
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Not sure what you mean by "doing mole-mole". I read the question as if 0.100 M was the equilibrium concentration, not the initial.
 
Borek said:
Not sure what you mean by "doing mole-mole". I read the question as if 0.100 M was the equilibrium concentration, not the initial.

Forgive me. Mole to mole ratio is what I meant to convey. Thank you for your input.
 
In other words you tried to calculate equilibrium concentration following the stoichiometry?

Where did you got OH- from?
 
Morgan Chafe said:

Homework Statement



Question 9)

View attachment 77944

Homework Equations



K=\frac{[P]}{[R]}

The Attempt at a Solution



What is confusing me is the wording. It merely says for the concentration of chromate. All this time we've been doing the equilibrium concentrations. Doing mole-mole with the Cr2O7 yields the answer to be D. I then assumed that it meant that they were the concentrations at equilibrium, which gave C to be the correct answer after preforming the equilibrium constant equation. Thanks for reading.

What is the expression for the equilibrium constant for this particular equilibrium?

True, it has [products] in the numerator and [reactants] in the denominator, but what do you do with the stoichiometric coefficients?

As Borek notes, they are giving you equilibrium values for the concentrations. If they weren't they would say something like "... the inital concentration of dichromate beofre equilibrium is reached is blah blah..."
 
Quantum Defect said:
As Borek notes, they are giving you equilibrium values for the concentrations. If they weren't they would say something like "... the inital concentration of dichromate beofre equilibrium is reached is blah blah..."

Yes. The issue was if they were equilibrium values or not. Usually it explicitly states.
 
Morgan Chafe said:
Yes. The issue was if they were equilibrium values or not. Usually it explicitly states.
What is the expression for the equilibrium constant, using concentrations? Where do the stoichiometric coefficients come in?
 

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