Why did my Biuret's test on eggwhite result in a brown color?

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Discussion Overview

The discussion revolves around the unexpected brown color observed in a Biuret test conducted on egg white, which is typically expected to yield a blue result for negative tests. Participants explore potential reasons for this anomaly, including the influence of pH, copper concentration, and the presence of reducing sugars.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant expresses confusion over the brown result of the Biuret test, seeking hints rather than direct answers.
  • Another participant suggests that the brown color could be due to an excess of CuSO4.
  • A third participant explains the Biuret test mechanism, noting that copper(II) is reduced to copper(I) in the presence of protein and complexes with nitrogen groups, typically resulting in a violet color at high pH.
  • Questions are raised regarding the effects of high pH or high copper concentration on the Biuret test results.
  • One participant acknowledges their understanding of the Biuret test but is puzzled by the brown color instead of the expected blue, speculating about the presence of reducing sugars in the egg white potentially affecting the outcome.
  • The participant also reflects on their experience during the report, indicating they rushed through the questions and provided incorrect answers due to their focus on the brown result.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the cause of the brown color, with multiple competing hypotheses presented and uncertainty remaining about the influence of various factors.

Contextual Notes

Limitations include the lack of specific details on the pH levels, copper concentration used, and the presence of other substances in the egg white that may affect the test results.

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I can't seem to figure out why the test came out as BROWN. I've been researching for HOURS and I can't find out why. I'm not asking any of you to give me an answer, but PLEASE throw me a hint. PLEASE. I heated the egg to 37C by the way.
 
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Did you add too much CuSO4?
 
Biuret is a test for protein. The copper(II) is reduced to copper(I) in the presence of protein and it complexes the nitrogen groups, turning violet at high pH.

Benedict's test is a test for reducing sugars. It contains copper(II) that reacts with the reducing sugar to produce a brick red ppt of copper(I) oxide.

What might happen if the pH were too high in the Biuret test or if the copper concentration were too high? What might happen if the protein test sample also contained reducing sugars?
 
I didn't add too much CuSO4 -_- there was an amount we were supposed to put. =P

Yes. I knew that about the Biuret's but the result for negative was supposed to be blue =S And it was BROWN. So yeah. It buffled me. So if eggwhite had a reducing sugar, would it have a brickred precipitate too? And I did the report but I just moved on quickly so the teacher wouldn't have enough time to ask what caused the brown instead of blue -_-

I slipped away but I focused to the brown thing that I didn't read the other questions properly so I answered wrong. Bad days.

Haha, sorry if I just pop in here when I need something. -_- Thank you for the hint though haha.
 

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