### Numerical Computation of pH and Buffer Capacity in Complex Mixtures of Acids, Bases and Ampholytes

*Prapaporn Boonme, Wibul Wongpoowarak, Damrongsak Faroongsarng, Nimit Worakul*

#### Abstract

This study was aimed to simplify the pH calculation for complex mixtures of acids, bases and ampholytes; the theoretical concept on pH calculation was renovated. A new algorithm was proposed to state that buffer capacity (β) could be simultaneously achieved with pH. To validate the method, the buffer systems of Na2HPO4/NaH2PO4 and Na2HPO4/citric acid were employed. Acid and base titration was done on the buffer systems using HCl and NaOH, respectively. It was demonstrated that only the charge balance equation (CBE) was necessary and sufficient to successfully compute β. To achieve the desirable accuracy, the pH interval used in such algorithm should be 10-4 for general calculation; between 10-4 and 10-2 for 8 significant-digits calculation; between 2 x 10-10 and 4 x 10-4 for 16 significant-digits calculation. Visual Basic Source Code written in Microsoft AccessTM for demonstrating computation of pH and β of pure water was also illustrated.

**Key Words**: pH; Buffer capacity; Computational prediction; AlgorithmFull Text: PDF