Understanding pH and Buffer Solutions: Acid-Salt Ratio and pKa vs. pH and pKb

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In summary, the conversation discusses the relationship between pH, pKa, and the amount of weak acid and salt needed to make a buffer solution. It is stated that if the pH is lower than the pKa, more acid is needed to lower the pH, and if the pH is higher than the pKa, more salt is needed. The same principle applies for pKb and pOH, with more salt needed if pKb is larger and more base needed if pKb is smaller. It is also mentioned that when preparing a buffer with a target pH, if pH = pKa, equal quantities of acid and salt are needed. However, if pKa = 14 - pKb, the reasoning may be more
  • #1
future_vet
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This is not a homework question, so I cannot give exact values or anything, sorry.

If we have to make a buffer solution, and we know the pH and the pKa of the acid we are going to use, would it be true to say that if the pH < pKa, we will need more of the weak acid than salt? If pH > pKa, we would need more salt?

Same thing for the pKb and pOH (14 - pH), would we need more salt if the pKb was bigger? More base if the pKb was smaller?

If we have to prepare a buffer with a target pH, and pH = pKa, we need the same quantity of acid and salt respectively, correct? (so that pKa = pH - log1, since log1=0)
BUT if we have pKa = 14 - pKb, what would be the reasonning then? I have a bit of trouble visualizing all that.

Thank you,

~J.
 
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  • #2
future_vet said:
If we have to make a buffer solution, and we know the pH and the pKa of the acid we are going to use, would it be true to say that if the pH < pKa, we will need more of the weak acid than salt? If pH > pKa, we would need more salt?

OK

Think in terms - add more acid to lower pH :smile:
 
  • #3
So my first part would be right?
If the pH is lower than the pKa we need more acid?

Thanks,

~J.
 
  • #4
Whatever pH you have, the only way to try to lower it is to add more acid. In concentrated solutions, or in case of really weak acid it may not work, but that's the only way of trying.
 
  • #5
Thank you!
 

1. What is the definition of pH?

pH is a measure of the acidity or basicity of a solution. It is determined by the concentration of hydrogen ions (H+) in a solution, with a lower pH indicating higher acidity and a higher pH indicating higher basicity.

2. How do buffer solutions work?

Buffer solutions are composed of a weak acid and its conjugate base, or a weak base and its conjugate acid. They work by resisting changes in pH when small amounts of acid or base are added to the solution.

3. What is the importance of maintaining a proper pH in biological systems?

Biological systems, such as the human body, require a specific pH range to function properly. Deviations from this range can lead to health problems and affect the functioning of enzymes and other important molecules.

4. How do you calculate the pH of a buffer solution?

The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation, which takes into account the concentration of the weak acid and its conjugate base, as well as the dissociation constant of the weak acid.

5. Can buffer solutions be used in other applications besides maintaining pH?

Yes, buffer solutions can also be used in biochemical and laboratory settings to maintain the pH of a solution during experiments, as well as in industrial processes to prevent changes in pH that could affect the quality of a product.

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