Sodium oxalate
| Sodium oxalate | ||
|---|---|---|
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| IUPAC name Sodium ethanedioate | ||
| Other names Oxalic acid, disodium salt | ||
| Identifiers | ||
| CAS number | 62-76-0  | |
| PubChem | 6125 | |
| EC number | 200-550-3 | |
| ChEMBL | CHEMBL182928  | |
| RTECS number | K11750000 | |
| Jmol-3D images | {{#if:C(=O)(C(=O)[O-])[O-].[Na+].[Na+]|Image 1 | |
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| Properties | ||
| Molecular formula | Na2C2O4 | |
| Molar mass | 134.00 g mol−1 | |
| Density | 2.34 g cm−3 | |
| Melting point | 260 °C (decomp.) | |
| Solubility in water | 3.7 g/100 mL (20 °C) 6.25 g/100 mL (100 °C) | |
| Solubility | insoluble in alcohol | |
| Hazards | ||
| MSDS | Oxford MSDS | |
| EU classification |  Xn | |
| NFPA 704 |
 0
3
0
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| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa) | ||
| Infobox references | ||
Sodium oxalate, or disodium oxalate, is the sodium salt of oxalic acid with the formula Na2C2O4. It is usually a white, crystalline, odorless powder, that decomposes at 250–270 °C.
Disodium oxalate can act as a reducing agent, and it may be used as a primary standard for standardizing potassium permanganate (KMnO4) solutions.
The mineral form of sodium oxalate is natroxalate. It is only very rarely found and restricted to extremely sodic conditions of ultra-alkaline pegmatites.[1]
Preparation
Sodium oxalate can be prepared through the neutralization of oxalic acid with sodium hydroxide (NaOH) in a 1:2 acid-to-base molar ratio. Half-neutralization can be accomplished with NaOH in a 1:1 ratio which produces NaHC2O4, monobasic sodium oxalate or sodium hydrogenoxalate.
Reactions
Sodium oxalate is used to standardize potassium permanganate solutions. It is desirable that the temperature of the titration mixture is greater than 60 °C to ensure that all the permanganate added reacts quickly. The kinetics of the reaction is complex, and the manganese(II) ions formed catalyze the further reaction between permanganate and oxalic acid (formed in situ by the addition of excess sulfuric acid). The final equation is as follows:[2]
- 5Na2C2O4 + 2KMnO4 + 8H2SO4 → K2SO4 + 5Na2SO4 + 2MnSO4 + 10CO2 + 8H2O
Biological activity
Like several other oxalates, sodium oxalate is toxic to humans. It can cause burning pain in the mouth, throat and stomach, bloody vomiting, headache, muscle cramps, cramps and convulsions, drop in blood pressure, heart failure, shock, coma, and possible death. Mean lethal dose by ingestion of oxalates is 10-15 grams (per MSDS).
Sodium oxalate, like citrates, can also be used to remove calcium ions (Ca2+) from blood plasma. It also prevents blood from clotting. Note that by removing calcium ions from the blood, sodium oxalate can impair brain function, and deposit calcium oxalate in the kidneys.
References
- ↑ http://rruff.geo.arizona.edu/doclib/hom/natroxalate.pdf Handbook of Mineralogy
- ↑ Mcbride, R. S. (1912). "The standardization of potassium permanganate solution by sodium oxalate". J. Am. Chem. Soc. 34: 393. doi:10.1021/ja02205a009.
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