AMMONIUM SULFATE CAS N°: 7783-20-2
AMMONIUM SULFATE CAS N°: 7783-20-2
AMMONIUM SULFATE CAS N°: 7783-20-2
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OECD SIDS<br />
<strong>AMMONIUM</strong> <strong>SULFATE</strong><br />
1.3 Physico-Chemical properties<br />
Table 1 Summary of physico-chemical properties<br />
Property Value Reference<br />
Physical state White solid BASF AG, 1999<br />
Melting point<br />
Upon heating in an open system, decomposition<br />
begins at temperatures between 150<br />
and 280 °C, depending on experimental<br />
conditions and purity of the test substance,<br />
and is complete at 336 -357 °C.<br />
Gmelin, 1936; CRC, <strong>20</strong>02<br />
Boiling point decomposes Gmelin, 1936<br />
Relative density 1.77 at 25 °C CRC, <strong>20</strong>02<br />
Vapour pressure<br />
4.053*10 -7 Pa (partial pressure of ammonia<br />
over solid (NH 4 ) 2 SO 4 at 25°C)<br />
Water solubility 764 g/l at <strong>20</strong> °C CRC, <strong>20</strong>02<br />
Scott and Cattell, 1979<br />
Partition coefficient-octanol/water<br />
(log Kow)<br />
–5.1 at 25 °C (OECD TG 107) */** BASF AG, 1988<br />
log Koc **<br />
Henry’s- Law -constant<br />
not assignable**<br />
pH 5 - 6 Frank, 1980<br />
pKa-values at 25°C<br />
Christen, 1973<br />
ammonium-ion (base ammonia)<br />
9.21<br />
sulfuric acid (base HSO 4 - )<br />
hydrogensulfate (base sulfate)<br />
–3<br />
1.92<br />
* The OECD test method 107 applies only to pure, water soluble substances which do not dissociate<br />
or associate and which are not surface active. Therefore the validity of this method for ammonium<br />
sulfate is uncertain.<br />
** Due to the ionic nature the calculation of log Kow, Henry’s-Law-constant, and log Koc via EPISUITE is not<br />
appropriate<br />
In aqueous solution, ammonium sulfate is completely dissociated into the ammonium ion (NH 4 + )<br />
and the sulfate anion (SO 4 2- ). Depending on pH, ammonia (NH 3 ) exists in equilibrium with the<br />
ammonium ion (NH 4 + ), according to the following relationship:<br />
NH 4 + + H 2 O NH 3 + H 3 O +<br />
In general, as pH increases, the fraction of the total ammonia which is un-ionized increases. For<br />
example, at 5 °C and pH 6.5, 0.0395 % of the total ammonia is present as NH 3 . Increasing the pH<br />
from 6.5 to 8.5 will increase the un-ionized ammonium by a factor of approximately 100 (Rice and<br />
Bailey, 1980). Increasing the temperature will also increase the percentage of unionized<br />
ammonium. For example, in seawater at 25 °C and pH of approximately 8.1, approximately 7 % of<br />
the total ammonia is present as NH 3 (Holt and Arnold, 1983).<br />
UNEP PUBLICATIONS 9
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