Tonicity and Osmoticity of saline with weak acid

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SUMMARY

The discussion focuses on the tonicity and osmoticity of a solution containing 150mM NaCl and 50mM of a weak acid with a pKa of 7.0 at a pH of 4. The key conclusion is that the solution remains isotonic due to the NaCl concentration while being hyperosmotic because the weak acid predominantly exists in its charged form at this pH, limiting its ability to diffuse across cell membranes. The equation log([A-]/[HA]) = pH - pKa is critical for understanding the dissociation of the weak acid in this context.

PREREQUISITES
  • Understanding of pH and pKa concepts
  • Knowledge of osmotic pressure and tonicity
  • Familiarity with weak acid dissociation
  • Basic principles of cell membrane permeability
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Biochemists, pharmacologists, and healthcare professionals involved in drug formulation and osmotic balance in biological systems will benefit from this discussion.

uzi kiko
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Hi all

I got an exercise:
Cells were floated in a mass in a solution with 150mM of NaCl (isotonic conditions). A weak acid was added to the solution with a pK of 7.0 and concentration of 50mM in the solution.
What is the tonicity and osmoticity of the new solution if PH=4

I know that I should use the following equation:
log([A-]/[HA]) = PH - pKa

But It seem that I am getting the wrong result.
Can somebody help?
 
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The answer in case somebody else will interest:

Need to understand that only the fraction of the drug that is uncharged can diffuse across membranes.
So in case PH=4 and pKa=7 the solution will be acidic so the weak acid remain almost in the same concentration (50mM)

so the solution is isotonic and hyperosmotic
 

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