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

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SUMMARY

The discussion focuses on the chemical reaction involving chromium ions and hydroxide ions to form chromium(III) hydroxide, represented by the equation Cr3+ + 3OH- → Cr(OH)3. Participants clarify the need for balancing both the number of atoms and the charges in the reaction. The correct balanced equation is 3Cr3+ + 9OH- → 3Cr(OH)3, which simplifies to Cr3+ + 3OH- → Cr(OH)3. Emphasis is placed on the importance of maintaining charge conservation alongside mass conservation in chemical equations.

PREREQUISITES
  • Understanding of chemical reactions and balancing equations.
  • Knowledge of polyatomic ions, specifically hydroxide (OH-).
  • Familiarity with oxidation states and charge conservation principles.
  • Basic chemistry concepts, including the formation of compounds from ions.
NEXT STEPS
  • Study the principles of balancing chemical equations in detail.
  • Learn about polyatomic ions and their roles in chemical reactions.
  • Research the concept of charge conservation in electrochemistry.
  • Explore the formation and properties of chromium(III) hydroxide (Cr(OH)3).
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Chemistry students, educators, and professionals involved in chemical research or education, particularly those focusing on inorganic chemistry and reaction mechanisms.

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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