### Abstract

Potentiometric measurements of the stoichiometric constants on the seawater pH scale for the dissociation of carbonic acid in seawater (K_{1}^{*} = [H^{+}][HCO_{3}^{-}]/[CO_{2}] and K_{2}^{*} = [H^{+}][CO_{3}^{2-}]/[HCO_{3}^{-}]) have been made as a function of salinity (1 to 50) and temperature (0 to 50 °C). The results have been fitted to the equations (T/K){A formula is presented}. The values of pK_{i}^{0} in pure water are taken from the early work of Harned and Davis (1943) and Harned and Scholes (1941){A formula is presented}{A formula is presented}. The value of the adjustable parameters A_{i}, B_{i} and C_{i} for pK_{1}^{*} are given by (σ = 0.0054 and N = 466){A formula is presented}{A formula is presented}{A formula is presented}. For pK_{2}^{*} the parameters are given by (σ = 0.011 and N = 458){A formula is presented}{A formula is presented}{A formula is presented}. The values of pK_{1}^{*} and pK_{2}^{*} determined in this study are in good agreement with the seawater (SW) measurements of Mehrbach et al. (1973) and Mojica-Prieto and Millero (2002) from S = 15 to 45 and 0 to 40 °C. The values of pK_{1}^{*} near S = 35 are also in reasonable agreement with the measurements in artificial seawater (ASW) of Goyet and Poisson (1989) and Roy et al. (1993) from 0 to 35 °C. The values of pK_{2}^{*} in real seawater, however, do not agree with the measurement made in artificial seawater at temperatures above 5 °C. Calculations of pK_{1}^{*} and pK_{2}^{*} near 25 °C using an ionic interaction model (Millero and Roy, 1997) suggest that the pK_{2}^{*} results in SW are more reliable than in ASW. The equations from this study should be valid from S = 0 to 50 and t = 0 to 50 °C for most estuarine and marine waters (check values at S = 35 and t = 25 °C are pK_{1}^{*} = 5.8401 and pK_{2}^{*} = 8.9636).

Original language | English (US) |
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Pages (from-to) | 80-94 |

Number of pages | 15 |

Journal | Marine Chemistry |

Volume | 100 |

Issue number | 1-2 |

DOIs | |

State | Published - Jun 1 2006 |

### Keywords

- Carbonic acid
- Dissociation constants
- Modeling
- Seawater
- Titration
- pK
- pK

### ASJC Scopus subject areas

- Oceanography
- Chemistry(all)
- Environmental Chemistry
- Water Science and Technology

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## Cite this

*Marine Chemistry*,

*100*(1-2), 80-94. https://doi.org/10.1016/j.marchem.2005.12.001