The dissociation of phosphoric acid in NaCl and NaMgCl solutions at 25°C |
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Authors: | J Peter Hershey Marino Fernandez Frank J Millero |
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Institution: | (1) Rosenstiel School of Marine and Atmospheric Science, University of Miami, Rickenbacker Causeway, 4600 Miami, FL, 33149 |
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Abstract: | The pK
1
*
, pK
1
*
and pK
3
*
for the dissociation of H3PO4 have been measured in NaCl solutions from 0.5 to 6m at 25°C. The results have been used to evaluate Pitzer interaction parameters (NaClH2PO4)=–0.028±0.005, (NaH3PO4)=–0.075±0.025, (HPO4Cl)=0.105±0.009, (PO4Cl)=–0.59±0.02 and (NaClHPO4)=–0.003±0.004, (PO4NaClH)=0.110±0.008. These parameters yield values of pK
1
*
, pK
2
*
and pK
3
*
in NaCl that agree with the measured values with average deviations of ±0.04, ±0.03 and ±0.05 in pK
1
*
. Measurements of pK
1
*
and pK
2
*
were also made in NaMgCl solutions. These results have been used to evaluate (O)(MgH
2
PO
4)=–3.55±0.07,(1)(MgH
2
PO
4=–16.9±0.03, (O)(MgH
2
PO
4=–17.5±0.03 and (1)(MgH
2
PO
4)=27.4±0.8 at 25°C. The results for pK
2
*
in NaMg–Cl solutions were also used to calculate log K
MX
*
=3.2±0.1 for the formation of the ion pair MgHPO
4
o
. |
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Keywords: | Phosphoric acid Pitzer equations ion pairing |
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