chem stories

Buffer solution is able to retain almost constant pH when small amount of acid/base is added. Quantitative measure of this resistance to pH changes is called buffer capacity.

Buffer capacity can be defined in many ways. You may find it defined as "maximum amount of either strong acid or strong base that can be added before a significant change in the pH will occur". This definition - instead of explaining anything - raises a question "what is a significant change?" - sometimes even change of 1 unit doesn't matter too much, sometimes - especially in biological systems - 0.1 unit change is a lot. Buffer capacity can be also defined as quantity of strong acid or base that must be added to change the pH of one liter of solution by one pH unit. Such definition - although have its practical applications - gives different values of buffer capacity for acid addition and for base addition (unless buffer is equimolar and its pH=pKa). This contradicts intuition - for a given buffer solution its resistance should be identical regardless of whether acid or base is added.



http://www.chembuddy.com/?left=pH-calculation&right=pH-buffer-capacity