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Environmental fate & pathways

Hydrolysis

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Description of key information

According to structural properties, hydrolysis is not expected/probable.

Key value for chemical safety assessment

Additional information

Ammonium bicarbonate is soluble in water at temperatures below 60°C from 10.6 % (w/w) at 0°C to 37.2 % (w/w) at 60 °C. It is decomposed by hot water.

Ammonium bicarbonate is an alkaline buffer. Ammonium ion (NH4+) is the acid of the NH3/NH4+ buffer system and bicarbonate ion (HCO3-) is the base of the HCO3-/CO2 buffer system, so that when ammonium bicarbonate is dissolved in pure water:

pH = 1/2 pKa +1/2 pKb.

 

To obtain the pKa value, the following equilibrium has to be considered:

NH3 + H2O ↔ OH- + NH4 +

Ka = ([NH3][H+]) / [NH4+]

 

The equilibrium constant Ka depends significantly on temperature; this relationship has been described by Emerson et al (1975) with the following equation:

pK = 0.09018 + [2729.92 / (273.2 + T)], where pK = -log10K and T is the temperature in degrees Celsius.

 

In general, as pH and temperature increases, the fraction of the total ammonia which is un-ionized increases. However, it should be noted that un-ionized ammonia is much more dependent on pH than on temperature.

 

To obtain the pKb value, the following equilibrium has to be considered:

CO2 + H2O ↔ HCO3- + H+ (pKb = 6.35)

No information has been found related to the effects of temperature on that equilibrium.

Reference:

OECD (2006). SIDS Ammonium bicarbonate CAS: 1066-33-7, Draft 2006