Thermodynamics of the dissociation of 2-aminopyridinium ion in synthetic seawater and a standard for pH in marine systems

Abstract

Buffer solutions composed of 2-aminopyridinium chloride and 2-aminopyridine in synthetic seawater are useful as a supplement to buffers of ‘Tris’ (pH 8.2) and ‘Bis’ (pH 8.8) in standardizing measurements of hydrogen ion concentration (pmH or pH(SWS)) in oceanography. The dissociation constant of 2-amino-pyridinium ion over the range of salinities (S) from 30 to 40 has now been determined from the emf of cells without liquid junction at eight temperatures (T) from 278.15 to 313.15 K. The results fit the equation pK=2498.31/T−15.3274+2.4050 lnT+S(0.012928−2.9417×10−5T) with a standard deviation of 0.0023. Thermodynamic constants for the dissociation process and standard reference values of pmH and pH(SWS) were derived from the data. The pmH of the buffer consisting of 2-aminopyridinium chloride and 2-aminopyridine (each 0.04 molal) in synthetic seawater of salinity 35 varies from 7.356 at 278.15 K to 6.601 at 313.15 K.