Discussion Overview
The discussion revolves around calculating the dissociation constant (Ka) for picric acid based on absorbance measurements of its solutions in a sodium hydroxide environment. Participants explore the relationship between absorbance, concentration, and the dissociation equilibrium of the acid.
Discussion Character
- Homework-related
- Mathematical reasoning
- Technical explanation
- Debate/contested
Main Points Raised
- One participant presents a homework problem involving absorbance measurements of sodium picrate and picric acid solutions, expressing uncertainty about how to proceed with the calculations.
- Another participant suggests converting absorbance values to concentrations and questions how much undissociated weak acid can be present in the sodium hydroxide solution.
- A participant clarifies that equilibrium concentrations are needed rather than total concentrations, raising questions about the relative concentrations of hydroxide and hydrogen ions in the solution.
- One participant attempts to set up an equilibrium expression for the dissociation constant but is unsure how to incorporate absorbance values into their calculations.
- Another participant critiques the understanding of the problem, emphasizing the need to determine the absorbance coefficient of the picrate anion in a high pH solution.
- A participant calculates the molar absorptivity of picric acid from its absorbance and concentration, questioning whether this value can be used for the mixture with sodium picrate.
- A later reply clarifies that the relevant absorptivity is that of the picrate anion and states that the contribution of sodium hydroxide to absorbance can be assumed negligible.
- Finally, a participant calculates the concentration of the picric anion based on the absorbance and proposes a value for the dissociation constant, though this is not universally accepted.
Areas of Agreement / Disagreement
The discussion contains multiple competing views regarding the approach to calculating the dissociation constant, and there is no consensus on the correct method or final value. Participants express differing opinions on the significance of hydroxide concentration and the appropriate use of absorbance data.
Contextual Notes
Participants highlight the need for equilibrium concentrations and the potential complexities introduced by the presence of sodium hydroxide, indicating that assumptions about ion concentrations may affect the calculations.
