Selenium Oxidation State in Redox Reaction

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Discussion Overview

The discussion revolves around the oxidation state of selenium in a redox reaction involving selenium oxide (SeO2) and chromium sulfate (CrSO4). Participants explore the stoichiometry of the reaction, the transfer of electrons, and the resulting products, while grappling with the implications of sulfate ions in the reaction.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant calculates the mole ratio of SeO2 to CrSO4 as 1:4, suggesting that one mole of SeO2 requires four moles of CrSO4 for the reaction.
  • Another participant proposes that selenium is reduced from an oxidation state of +4 to 0, receiving four electrons from chromium, which is oxidized from +2 to +3.
  • Concerns are raised about the presence of sulfate ions in the reaction, with one participant questioning the formation of selenium sulfate and suggesting the possibility of sulfuric acid formation instead.
  • One participant expresses uncertainty about the correctness of their approach and the overall reaction, seeking clarification from others.
  • Another participant notes that selenium can have multiple oxidation states, including +6, +4, +1, and -2, and questions the existence of selenium sulfate.
  • A later reply confirms the previous assertion that selenium is reduced, while chromium is oxidized, but does not provide a definitive conclusion on the oxidation state of selenium.
  • There is a request for clarification on the fate of sulfate ions in the reaction.

Areas of Agreement / Disagreement

Participants express differing views on the oxidation state of selenium and the products of the reaction. While some agree on the reduction of selenium and oxidation of chromium, there is no consensus on the final oxidation state of selenium or the role of sulfate ions.

Contextual Notes

Participants rely on stoichiometric relationships and assumptions about the reaction conditions, but there are unresolved questions regarding the formation of products and the behavior of sulfate ions.

Who May Find This Useful

This discussion may be of interest to students and practitioners in chemistry, particularly those studying redox reactions and oxidation states.

ShakeWell
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Redox question:

12.53 ml of .05093 M selenium oxide (SeO2) reacted exactly with 25.52 ml of .1 M CrSO4. Cr+3 is formed. To what oxidation state is Selenium converted?

I think that the ml + M stuff gives you the ratio between moles of SeO2 and moles of CrSO4 (1m SeO2 = 4m CrSO4). But how am I supposed to figure out what happens to the Se?
 
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Okay, this is how I'm looking at it, based solely on the information alone and not by looking up the oxidation states of selenium. I don't know if it's right but...
Ratio is 1:4, we know that, and we also know that chromium goes from +2 to +3. So SeO2 needed 4 moles of CrSO4 and so it follows that it needed 4 moles of e- from the Cr+2. So one SeO2 receives 4 e-'s and makes the reduction: Se(+4) + 4e- --> Se(0) which is the selenium metal.

Wow it looks so nice, we've solved the problem, and I don't know if it's right. Something came up though, when you write out the equation there's a problem with the sulfate ion floating around:

SeO2 + CrSO4 --> Se + Cr2O3 + SO4(-2)

so maybe it reacts with the water in the solution (assuming everything's aqueous and it probably is), and forms H2SO4.

2H+ + SeO2 + 4CrSO4 --> Se + 2Cr2O3 + H2SO4

I don't think this is right, so can someone please help.
 
someone care to help? I'm sorry but I just really want to know the answer, it bugs me when I can't solve a problem.
 
I'm thinking its 2+, that is it has been reduced while the chromium has been oxidized. Nonmetalic elements usually have oxidation states at even intervals e.g. from 4+ to 2+. Tis an oxidation reduction reaction.
 
Se has oxidation states of +6, 4, 1, and -2. +1 being very rare. http://www.ivstandards.net/extras/pertable/
Regardless though, based on the information that was given and my reasoning, was it a correct approach?
And selenium sulfate doesn't exist, I can't find it on chemfinder, so I don't think that that will even form. SO what the hell is going on...
 
Chromium is oxidized, which means it has lost some electrons. Therefore it is a reducing agent; something has been reduced. Selenium is reduced. If the original assumption was right-1 Se for every 4 Cr, than we can assume that 4 electrons are lost for every 1 Se. Assuming that the original oxidation state of Se was 4+ we can say that the oxidation state for Se is now 0. However, I am not completely sure about this. I'll check back later with other details, I am a bit busy right now.
 
Yeah, the above is correct.
 
thanks.
what happens to SO4(2-)?
 

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