How do buffers resist pH change?

Answer 1

Well, they usually do so superbly, depending on the capacity of the buffer.

The defining equation is:

#pH=pK_a+log_10{[[A^-]]/[[HA]]}#

And thus an equimolar solution of a weak acid and its conjugate base will maintain a #pH# close to the #pK_a# of the acid should small quantities of acids or bases be added. Biological systems are extensively buffered.

See here for its derivation.

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Answer 2

Jeremiah Adams

Buffers resist pH change by containing a weak acid and its conjugate base (or a weak base and its conjugate acid). When an acid or base is added to the buffer solution, the equilibrium between the weak acid and its conjugate base (or weak base and its conjugate acid) shifts to counteract the pH change, minimizing the overall effect on the pH of the solution.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.