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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
other: expert statement
Adequacy of study:
key study
Study period:
2010-08-02
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Expert statement
Qualifier:
no guideline followed
Principles of method if other than guideline:
expert statement
Transformation products:
not specified
Remarks:
Please refer to "any other information on results incl. tables"
Key result
Remarks on result:
other: The hydrolysis of carbonates is a well known chemical process. Please refer to "Any other information on results incl tables".

Lithium carbonate is an inorganic salt with a molecular weight of 73.89 g/mol.

It is limited soluble in water, revealing a water solubility of 8.4 - 13 g/L at 20 °C.

  

Lithium carbonate dissociates in water:

  

Li2CO3(s) + aq ↔ 2 Li+(aq) + CO3^2- (aq)

  

Hydrolysis of lithium carbonate produces basic solutions by generating lithium hydroxide and lithium hydrogen carbonate.

  

The carbonate ion is the conjugate base of an extremely weak acid (carbonic acid). It strongly attracts protons from H2O molecules to give a solution with a pH of ca. 11.

  

Li2CO3+ H2O ↔ LiHCO3+ LiOH

  

In contrast, the hydrogen carbonate ion (HCO3-(aq)), with its single negative charge, has lower surface charge density than the carbonate ion and is a considerably weaker base. It exerts a feeble attraction for protons and the pH of the solution only reaches a pH of ca. 8.3.

  

With acid (decreasing pH) the respective lithium salt and carbon dioxide are formed.

  

pH values can be calculated for certain molar Li2CO3 and LiHCO3 solutions by

pKa (H2CO3) = 9.35 and

pKa (HCO3-) = 10.33.

  

The pH of a 0.02 mol solution is calculated to be 11.3.

  

With respect to its environmental fate in water, the carbonate ions will re-equilibrate until equilibrium is established.

The relevant equilibria are:

  

HCO3-↔ CO3^2-+H+

pKa = 10.33

  

CO2+ H2O↔HCO3-+ H+

pKa = 6.33

  

The main part of the dissolved CO2 is present as CO2 and not as H2CO3.

The amount of CO2 in water is in equilibrium with the partial pressure of CO2 in the atmosphere.

The CO2/ HCO3-/ CO3^2-equilibria are the major buffer of the pH of freshwater and seawater.

  

Based on the above equations, CO2 is the predominant species at a pH smaller than 6.33.

HCO3- is the predominant species at a pH in the range of 6.35-10.33.

CO3^2- is the predominant species at a pH higher than 10.33.

  

The carbonate will finally be incorporated into the inorganic and organic carbon cycle.

  

References

  

Nylén, P.; Wigren, N.; Joppien, G. (1991):Einführung in die Stöchiometrie; Kurzes Lehrbuch der allgemeinen und physikalischen Chemie, 19. korrigierte Auflage 112-113; ISBN 3-7985-0803-8

  

OECD SIDS SODIUM CARBONATE CASN°: 497-19-8; UNEP Publication, 2002.

 

Conclusions:
Lithium carbonate is an inorganic salt that is soluble in water (8.4 – 13 g/L at 20 °C)
Hydrolysis of lithium carbonate produces basic solutions by generating lithium hydroxide and lithium hydrogen carbonate. The pH values can be calculated based on pKa values.
The pH of a 0.02 mol solution is calculated to be 11.3.
In water CO2 is the predominant species at a pH smaller than 6.33, HCO3- (hydrogen carbonate ion) at a pH in the range of 6.35-10.33, and CO32- (carbonate ion) at a pH higher than 10.33.

Executive summary:

Instead of an experimental study, an expert statement about the hydrolytical behaviour of lithium carbonate is provided: lithium carbonate is an inorganic salt with a molecular weight of 73.89 g/mol. It is limited soluble in water, revealing a water solubility of 8.4 - 13 g/L at 20 °C. Lithium ions do not undergo abiotic degradation. Hydrolysis of lithium carbonate produces basic solutions of lithium hydroxide and lithium hydrogen carbonate. Formed carbonates hydrolyse further by a well known chemical process. The pH values can be calculated based on pKa values. The pH of a 0.02 mol solution is calculated to be 11.3. In water CO2 is the predominant species at a pH lower than 6.33, HCO3- (hydrogen carbonate ion) at a pH in the range of 6.35-10.33, and CO3^2- (carbonate ion) at a pH higher than 10.33.

Description of key information

The hydrolysis of carbonates is a well known chemical process. Hydrolysis of lithium carbonate produces basic solutions by generating lithium hydroxide and lithium hydrogen carbonate. The pH values can be calculated based on pKa values. The pH of a 0.02 mol solution is calculated to be 11.3. In water CO2 is the predominant species at a pH lower than 6.33, HCO3- (hydrogen carbonate ion) at a pH in the range of 6.35-10.33, and CO32-(carbonate ion) at a pH higher than 10.33. The carbonate will finally be incorporated into the inorganic and organic carbon cycle.

Key value for chemical safety assessment

Additional information

Lithium carbonate is an inorganic salt with a molecular weight of 73.89 g/mol.

It is limited soluble in water, revealing a water solubility of 8.4 - 13 g/L at 20 °C.

  

Lithium carbonate dissociates in water:

  

Li2CO3(s) + aq ↔ 2 Li+(aq) + CO3^2- (aq)

  

Hydrolysis of lithium carbonate produces basic solutions by generating lithium hydroxide and lithium hydrogen carbonate.

  

The carbonate ion is the conjugate base of an extremely weak acid (carbonic acid). It strongly attracts protons from H2O molecules to give a solution with a pH of ca. 11.

  

Li2CO3+ H2O ↔ LiHCO3+ LiOH

  

In contrast, the hydrogen carbonate ion (HCO3-(aq)), with its single negative charge, has lower surface charge density than the carbonate ion and is a considerably weaker base. It exerts a feeble attraction for protons and the pH of the solution only reaches a pH of ca. 8.3.

  

With acid (decreasing pH) the respective lithium salt and carbon dioxide are formed.

  

pH values can be calculated for certain molar Li2CO3 and LiHCO3 solutions by

pKa (H2CO3) = 9.35 and

pKa (HCO3-) = 10.33.

  

The pH of a 0.02 mol solution is calculated to be 11.3.

  

With respect to its environmental fate in water, the carbonate ions will re-equilibrate until equilibrium is established.

The relevant equilibria are:

  

HCO3-↔ CO3^2-+H+

pKa = 10.33

  

CO2+ H2O↔HCO3-+ H+

pKa = 6.33

  

The main part of the dissolved CO2 is present as CO2 and not as H2CO3.

The amount of CO2 in water is in equilibrium with the partial pressure of CO2 in the atmosphere.

The CO2/ HCO3-/ CO3^2-equilibria are the major buffer of the pH of freshwater and seawater.

  

Based on the above equations, CO2 is the predominant species at a pH smaller than 6.33.

HCO3- is the predominant species at a pH in the range of 6.35-10.33.

CO3^2- is the predominant species at a pH higher than 10.33.

  

The carbonate will finally be incorporated into the inorganic and organic carbon cycle.

  

References

  

Nylén, P.; Wigren, N.; Joppien, G. (1991):Einführung in die Stöchiometrie; Kurzes Lehrbuch der allgemeinen und physikalischen Chemie, 19. korrigierte Auflage 112-113; ISBN 3-7985-0803-8

  

OECD SIDS SODIUM CARBONATE CASN°: 497-19-8; UNEP Publication, 2002.

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