Chromium Ions in Water: Balancing Cr3++ and OH- to Form Cr(OH)3

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Discussion Overview

The discussion revolves around the chemical reaction involving chromium ions and hydroxide ions to form chromium(III) hydroxide, Cr(OH)3. Participants explore the balancing of the reaction equation, focusing on the coefficients and the conservation of charge and mass in the reaction.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that the correct coefficient for OH- should be 9, arguing that the 3+ charge of Cr3+ requires three OH- ions to balance it, leading to a total of three O atoms.
  • Another participant clarifies that the coefficient in front of OH- is indeed 3, as each OH- has a charge of -1, which balances the Cr3+ charge.
  • A later reply expresses skepticism about the original question, proposing that the reaction should be represented as 3Cr3+ + 9OH- → Cr(OH)3, indicating confusion about the coefficients used in the reaction.
  • Another participant emphasizes the importance of balancing both the number of atoms and the charges in the reaction, suggesting that the equation must reflect both mass and charge conservation.

Areas of Agreement / Disagreement

Participants express differing views on the correct coefficients for the reaction, with no consensus reached on the appropriate representation of the balanced equation.

Contextual Notes

There are unresolved issues regarding the treatment of charges in the reaction, and participants highlight the necessity of balancing both atoms and charges in chemical equations.

Dalek1099
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Cr3++?OH-→ Cr(OH)3

I think it should be 9 but the mark scheme says 3 but accept correct multiples because the 3+ charge has to be canceled by 3- and this has to produce 3 O
 
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What are you wanting to know? ...Are you wondering about the coefficient in front of the OH?
Because that is 3.

Each OH- has a charge of -1 (it's one of those polyatomic ions).
So the Cr+3 and 3 OH- ions cancel each other out and is neutral overall.

I hope I answered what you wanted to know...
Sorry if I didn't realize you were asking something else!
 
Lo.Lee.Ta. said:
What are you wanting to know? ...Are you wondering about the coefficient in front of the OH?
Because that is 3.

Each OH- has a charge of -1 (it's one of those polyatomic ions).
So the Cr+3 and 3 OH- ions cancel each other out and is neutral overall.

I hope I answered what you wanted to know...
Sorry if I didn't realize you were asking something else!

I still think its dodgy because you are producing 3 OH so need 9 like in electrolysis, where 2O2-→4e- + O2 on the principle of that it should be 9 but I'm thinking the question itself is incorrect because it should be 3Cr3++9OH-→Cr(OH)3
 
You just have to make sure there is the same number of elements on each side.


3Cr+3 + 9OH-→Cr(OH)3

This isn't balanced because there are 3 Cr's on the left, and only 1 Cr on the right.
And on the left, there's 9 OH's, but on the right, there's only 3 OH's.

To balance this, you could add a 3 coefficient to the right side.

Then you'd have:

3Cr + 9OH --> 3Cr(OH)3

Now there are 3 Cr's on each side, and 9 OH's on each side.

*But this can be simplified further.
Just divide each coefficient by 3, and you'd get the correct formula:

Cr + 3OH --> Cr(OH)3
 
You are both inconsistent in treating charges - please always list them, as they are as important as atoms are. Reaction equation needs to have both atoms and charge balanced - atoms reflect mass conservation, charge reflects charge conservation
 

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