Altering pH of a luminol solution

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Discussion Overview

The discussion revolves around altering the pH of a luminol solution while maintaining its chemical properties. Participants explore methods to achieve a pH range from 7 to 14, considering the implications of such changes on the solution's chemistry.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant provides a recipe for luminol solution and inquires about altering its pH without affecting its chemistry.
  • Another participant asserts that it may not be possible to alter the pH significantly without causing copper hydroxide to precipitate, thus changing the chemistry of the solution.
  • Some participants suggest identifying the buffer components in the solution as a way to consider pH adjustments.
  • A question is raised about using NaOH to change the pH, with a follow-up inquiry regarding the impact of the volume of water used in the solution.
  • It is noted that while adding NaOH will change the pH, adjusting the ratio of conjugates to create a buffer may allow for some pH variation, though not far from the original pH.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of altering the pH without affecting the chemistry of the luminol solution. There is no consensus on a definitive method to achieve the desired pH range while maintaining the solution's properties.

Contextual Notes

Participants mention the potential precipitation of copper hydroxide and the role of buffers, indicating that assumptions about the solution's chemistry and the effects of pH changes are not fully resolved.

ChanYoung Park
The recipe for luminol solution that I found on the internet is:
0.2g luminol, 4.0g Na2CO3, 24.0g NaHCO3, 0.5g (NH4)2CO3, 0.4g CuSO4 dissolved in 1 dm3 of water.
How can I alter the pH of the solution to get a range of pH values from 7 to 14 without affecting the chemisty of the solution?
 
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Very general answer: you can't. At some point copper hydroxide will precipitate, and the "chemistry" of the solution will change.

Less general answer: identify buffer in the solution, think how you can change its pH.
 
Borek said:
Very general answer: you can't. At some point copper hydroxide will precipitate, and the "chemistry" of the solution will change.

Less general answer: identify buffer in the solution, think how you can change its pH.
What if I use NaOH and luminol dissolved in 1 dm3 water?
 
ChanYoung Park said:
What if I use NaOH and luminol dissolved in 1 dm3 water?

Why the volume? What if you used them dissolved in 2 dm3 water?

Yes, adding NaOH will definitely change pH. But as I said earlier, you can as well change ratio of conjugates making a buffer and prepare solution of a different pH. You won't get far from the original pH this way though.
 

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