Pressure Dependence of Weak Acid Ionization in Deuterium Oxide Solutions

Abstract

The pressure dependence of solution pH for acetate, cacodylate, phosphate, and TRIS buffers in deuterium oxide solutions was measured with the optical pH indicators 2,5-dinitrophenol and p-nitrophenol up to a pressure of 300 MPa. The results give the pressure dependence of the weak acid ionization constant for these buffers in D2O solution. Neuman et al. [J. Phys. Chem. 1972, 77, 2687] measured the pressure dependence of Ka for these buffers in H2O solutions and used the equation RT ln(Kp/Ko) = −ΔVa° P + 0.5 Δκ°P2 to describe the observed results where ΔVa° is the limiting volume change on ionization at atmospheric pressure and Δκ° reflects the pressure dependence of ΔVa°. The present experiment shows that there is no significant deuterium isotope effect on the pressure dependence for these weak acid ionization constants.