# Concentration of both buffers is the same, only the pH is different

• Sayantan21
In summary, the conversation discusses the use of the Henderson Hesselbach equation to solve a problem involving phosphoric acid. It is mentioned that the log part and pKa are the same, causing confusion. The discussion then shifts to the complexity of phosphate due to its tribasic nature and the need to consider the equilibrium between H2PO4- and HPO42- in the region of pH 7. The conversation also touches on the maximum buffering power at pH = pK and the question of which buffer is closer to that pH. The key consideration is the direction in which adding acid will take you - towards a region of greater or less buffering.
Sayantan21
Homework Statement
You are given two buffers [a) 0.1 M phosphate buffer of pH 7.7 and (b) 0.1 M phosphatebuffer at pH 6.71 . If acid is to be added to the buffers, which of them, do you think, will resist the pH changes better
Relevant Equations
Henderson Hesselbach Equation
pH = pKa + log([ conjugate base] /[ acid])
Here I used Henderson Hesselbach equation in both the cases , I.e
pH= pKa + log( [(PO4)3-]/ [H3PO4]) here pKa of phosphoric acid is 2.16 but the problem Is in both the cases the log part is same and Pka is also same so both will cancel out, and how can we solve? It is confusing.

Phosphate is complicated because phosphoric acid is tribasic, so there are several equilibria. (See e.g. Wikipedia article on phosphoric acid.) In the region of pH 7, you only really need to consider the equilibrium between H2PO4- and HPO42-. 0.1M is the total concentration of phosphate species; the individual species will change with pH.

So how will I know which will resist the pH better? Both are same buffers, with same Pka value

berkeman
You do know buffering power is maximum at pH = pK. ?
So that might be an easy question, which buffer is at the pH nearer to the pK?
However if I am not mistaken they are both equally distant.
So it is a question of in which direction are you going - and is adding acid taking you into a region of greater buffering or less?

## 1. What is the purpose of using buffers with different pH levels?

Buffers are used in scientific experiments and procedures to maintain a stable pH level. By using buffers with different pH levels, scientists can control the acidity or alkalinity of a solution and ensure that the pH remains constant.

## 2. How do buffers with different pH levels affect the concentration of a solution?

The concentration of a solution is not affected by the pH level of the buffer used. Both buffers have the same concentration and only differ in their ability to maintain a specific pH level.

## 3. Can buffers with different pH levels be used interchangeably?

No, buffers with different pH levels cannot be used interchangeably. Each buffer is designed to maintain a specific pH level, so using the wrong buffer can result in an incorrect pH and potentially affect the outcome of the experiment.

## 4. What happens if the concentration of both buffers is not the same?

If the concentration of both buffers is not the same, it can lead to an incorrect pH level. This can affect the stability of the solution and potentially alter the results of the experiment.

## 5. How can I determine the appropriate buffer to use for my experiment?

The appropriate buffer to use for your experiment will depend on the desired pH level of the solution. It is important to choose a buffer with a pH close to the desired pH and ensure that the concentration of the buffer is appropriate for your experiment.

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