Solubility of the Sodium and Ammonium Salts of Oxalic Acid in Water with Ammonium Sulfate

Abstract

The solubility of the sodium and ammonium salts of oxalic acid in water with ammonium sulfate present has been studied using differential scanning calorimetry, X-ray crystallography, and infrared spectroscopy. The crystals that form from aqueous mixtures of ammonium sulfate/sodium hydrogen oxalate were determined to be sodium hydrogen oxalate monohydrate under low ammonium sulfate conditions and ammonium hydrogen oxalate hemihydrate under high ammonium sulfate conditions. Crystals from aqueous mixtures of ammonium sulfate/sodium oxalate were determined to be ammonium oxalate monohydrate under moderate to high ammonium sulfate concentrations and sodium oxalate under low ammonium sulfate concentrations. It was also found that ammonium sulfate enhances the solubility of the sodium oxalate salts (salting in effect) and decreases the solubility of the ammonium oxalate salts (salting out effect). In addition, a partial phase diagram for the ammonium hydrogen oxalate/water system was determined.

Deliquescence Relative Humidities of Organic and Inorganic Salts Important in the Atmosphere

“…DRH experiments as a function of temperature were performed for sodium hydrogen oxalate monohydrate (NaHC 2 O 4 ·H 2 O, the solid that forms at room temperature from an aqueous solution that is 1:1 NaOH/H 2 C 2 O 4 ) both with and without ammonium sulfate present. The DRH for NaHC 2 O 4 ·H 2 O was determined to be greater than 95% for 298 and 308 K (and by implication 288 K since DRH increases with decreasing temperature), which is the RH limit of our experimental technique.…”

“…We then determined the onset DRH of solids completely dried from mixtures of NaHC 2 O 4 and (NH 4 ) 2 SO 4 . Buttke et al determined that the ratio of (NH 4 ) 2 SO 4 /NaHC 2 O 4 in saturated solution determines which solids form. For high (NH 4 ) 2 SO 4 /NaHC 2 O 4 ratio, ammonium hydrogen oxalate hemihydrate (NH 4 HC 2 O 4 ·0.5H 2 O) is the least soluble solid at room temperature, while at low (NH 4 ) 2 SO 4 /NaHC 2 O 4 ratio, NaHC 2 O 4 ·H 2 O is the least soluble solid at room temperature (see summary in Table ).…”

“…At high (NH 4 ) 2 SO 4 /NaHC 2 O 4 ratios, NH 4 HC 2 O 4 ·0.5H 2 O is the least soluble solid . Ammonium and sulfate ions are in large excess in the solution such that upon further drying (NH 4 ) 2 SO 4 will likely be one of the precipitates.…”

Oxalic Acid Adsorption on Rutile: Molecular Dynamics and ab Initio Calculations

“…Specifically, they measured the dissociation constants of oxalic acid in different ionic media over a range of ionic strengths. The microsolvation of oxalic acid in pure water was examined by ab initio calculations. , The important role of (NH 4 ) 2 SO 4 in oxalic acid solvation processes resulted in the solubility of oxalic acid salts being measured . The dissociated forms of oxalic acid (Figure ), namely, oxalate dianion (COO – ) 2 , abbreviated henceforth as ox -2 to indicate its charge, and hydrogenoxalate (also known as bioxalate) H­(COO – ) 2 , abbreviated as ox -1, have also been studied.…”

“…33,34 The important role of (NH 4 ) 2 SO 4 in oxalic acid solvation processes resulted in the solubility of oxalic acid salts being measured. 35 The dissociated forms of oxalic acid (Figure 1), namely, oxalate dianion (COO − ) 2 , abbreviated henceforth as ox-2 to indicate its charge, and hydrogenoxalate (also known as bioxalate) H(COO − ) 2 , abbreviated as ox-1, have also been studied. For example, Dean 36 described the stability of different conformers of ox-2, whereas Mohajeri et al 37 were interested in intramolecular hydrogen bonding of ox-1 and neutral oxalic acid in the gas phase.…”