The most common pH 10 Buffer Tablet is the " Mixture of Sodium bicarbonate and Sodium carbonate . ( NaHCO3 + Na2CO3 Mixture )
Buffer is a mixture of [ Weak Acid + Conjugate Base Salt ] or [ Weak Base + Conjucate Acid Salt ].
Buffer will give best performance if the Acid - Base Pair have equal concentation ( 1 : 1 ) .
In this case .. ( pH 10 Buffer Solution )
" Weak Acid " is the HCO3^- in NaHCO3
" Conjugate Base Salt " is the CO3^-- in Na2CO3
pH of Solution = pKa of HCO3^- + log [ CO3^-- ] / [ HCO3^- ]
pKa of HCO^3- is about 10.3 , which make it easy to set up a pH 10 solution .. ( by adjusting ratio of HCO3^- : CO3^--
When diluted with water , [ CO3^-- ] / [ HCO3^- ] will not be significantly changed . So the pH will be still at around 10 .
Addition of Acid will consume CO3^-- and generate more HCO3^-
Addition of Base will consume HCO3^- and generate more CO3^--
Once the quantity of added acid ( or added base ) is large enough to react with most ( more than 90 % ) of HCO3^- or CO3^-- . pH of this solution will change up to one pH unit or more . And solution is considered to lost its buffer property .