Question

In your experiment, you are instructed to create a buffer that is equal molar in acid...

In your experiment, you are instructed to create a buffer that is equal molar in acid and base components. You are given the concentration but not the pH. Why is it unnecessary for you to have been given the pH? Explain.  Be specific and detailed in your answers.  

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Answer #1

At equimolar quantity of acid and base components , the pH of buffer is equal to pKa of the acid.So , It is not necessary to indicate pH while preparing a buffer solution with equimolar quantity of acid and base components. This can be explained by Henderson Hasselbalch equation.

Henderson Hasselbalch equation is

pH =pKa + log([A-]/[ HA])

For example you are preparing Acetate buffer solution which is 0.5M in CH3COOH and 0.5M in CH3COO-

pKa of acetic acid = 4.75

pH = 4.75 + log(0.5/0.5)

= 4.75 + 0

= 4.75

So, pH = pKa

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