Identify Spectator: Bromide Reacts with Acidified NaClO4 - Test Tomorrow

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Discussion Overview

The discussion revolves around identifying spectator ions in a chemical reaction involving potassium bromide (KBr) and acidified sodium perchlorate (NaClO4). Participants explore the oxidation of bromide ions and the formation of bromine, questioning the role of bromide as a spectator ion in this context.

Discussion Character

  • Homework-related
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant expresses confusion about how to identify the spectator ions, specifically questioning the mass of bromine produced if bromide is a spectator.
  • Another participant asserts that bromide cannot be a spectator if it is oxidized from Br- to Br2, suggesting that writing the balanced equation is essential for solving the problem.
  • There is a discussion about whether bromide can be considered a spectator based on the formation of bromine and the nature of the reaction.
  • Some participants propose that if bromine is a product, the reaction must be a redox reaction rather than a double displacement reaction.
  • One participant questions if bromide would be a spectator if the question did not state Br2 as a product, indicating uncertainty about the criteria for identifying spectator ions.
  • Another participant emphasizes that the presence of soluble reactants and products means that all ions could be spectators, depending on the balanced equation used.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the identification of bromide as a spectator ion, with multiple competing views on the criteria for determining spectator ions based on the reaction context and products.

Contextual Notes

Participants highlight the importance of the balanced equation and the nature of the reaction (redox vs. double displacement) in determining the role of bromide. There is also mention of the solubility of the compounds involved, which affects the interpretation of spectator ions.

Suy
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I am really confused on how to identify the spectator. Like this question
what mass of bromine will be produced if a potassium bromide solution reacts with 50.0mL of a 1.20 mol/L solution of acidified NaClO4?
How is the mass formed, when bromide is a spectator?
i have a test tomorrow, if anyone can help me...
ty!
 
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This should really be in the homework section, but let's start with the obvious:

How can bromide be a spectator when it is oxidized from Br- to Br2?

Try writing the balanced equation for the reaction. (Actually, this should always be the first step to solving a problem)
 
PhaseShifter said:
How can bromide be a spectator when it is oxidized from Br- to Br2?

Try writing the balanced equation for the reaction. (Actually, this should always be the first step to solving a problem)

But how would you know if bromide is oxidized ? is it just because the question asked what mass of bromine is formed?
For this, if sodium phosphate react with calcium bromide,then phosphate and bromide will be the spectator..
But how do determine whether bromide is a spectator or not?
btw,KBr+NaClO4-->KClO4+NaBr
is that right?
ty!
 
Last edited:
The question states that reactants are KBr (aq) and NaClO4 (aq), and one of the products is Br2.

If the bromine starts as Br- and ends up as Br2, it must have been oxidized by something...and therefore can't be a spectator.

It's also no coincidence that perchlorates are powerful oxidizing agents.
 
Last edited:
KBr+NaClO4-->KClO4+NaBr
Sorry, it still doesn't make sense to me...
I don't see how is Br2 formed...
unless my equation is wrong..
 
Suy said:
KBr+NaClO4-->KClO4+NaBr
Sorry, it still doesn't make sense to me...
I don't see how is Br2 formed...
unless my equation is wrong..

Your equation is wrong...the problem states that Br2 is a product, so it must be a redox reaction rather than double displacement reaction.
 
PhaseShifter said:
Your equation is wrong...the problem states that Br2 is a product, so it must be a redox reaction rather than double displacement reaction.

Is that mean, if the question didn't state Br2 as a product, then Br will be a spectator?
 
Not always...for example the problem could ask about one of the other products of the same reaction.

But what is relevant in this case, is the problem asks how much Br2 is formed...which means an equation without Br2 among the products is not useful for solving the problem, and another equation must be used.

Also, your equation doesn't work because both products are soluble as well as both reactants...meaning all four compounds would be completely dissociated into solvated ions, which would mean all the ions are spectators, and no reaction occurs according to that equation.

Consider the electronegativities of bromine and chlorine, and look at the oxidation numbers in both reactants.
 
Last edited:
Thanks, that's make sense to me now. It's all depend how the question ask..
 

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