Question

Suppose NaOH is added too quickly, so that the NaOH volume appears higher at the stoichiometric point. How does this affect the calculated moles of acid? How does this affect the acid’s calculated molar mass? How does the increased volume affect the determination of pKa?

Answer 1

Acid Reacts with NaOH , so if we add NaOH excess than needed we also over estimate acid moles i.e we calculate higher moles of acid than original.

Molar mass = mass/ Moles

hence as we calculate more moles of acid than original we calculate Less Molar mass than original ( See eq at top less moles means more Molar mass for same amount of mass of acid)

Ka = [ H+] [A-] /[HA]          where HA is acid

so since we calculate more HA , we calculate less Ka

pka = -log Ka , hence we calculate more pka