Sodium oxalate

Sodium oxalate
Names
IUPAC name
Sodium ethanedioate
Other names
Oxalic acid, disodium salt
Sodium ethanedioate
Identifiers
62-76-0 Yes[1]
ChEMBL ChEMBL182928 
EC number 200-550-3
Jmol-3D images Image
PubChem 6125
RTECS number K11750000
Properties
Na2C2O4
Molar mass 133.999 g mol−1
Density 2.34 g cm−3
Melting point 260 °C (500 °F; 533 K) decomposes
2.69 g/100 mL (0 °C)
3.7 g/100 mL (20 °C)
6.25 g/100 mL (100 °C)
Solubility soluble in formic acid
insoluble in alcohol, ether
Structure
Crystal structure monoclinic
Thermochemistry
Std enthalpy of
formation (ΔfHo298)
 -1318 kJ/mol
Hazards
MSDS Oxford MSDS
EU classification Xn
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
0
3
0
11160 mg/kg (oral, rat)[2]
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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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.[3]

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.

Alternatively, it can be produced by decomposing sodium formate by heating it at a temperature exceeding 360 °C.

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:[4]

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

  1. ↑ http://chem.sis.nlm.nih.gov/chemidplus/rn/62-76-0
  2. ↑ http://chem.sis.nlm.nih.gov/chemidplus/rn/62-76-0
  3. ↑ http://rruff.geo.arizona.edu/doclib/hom/natroxalate.pdf Handbook of Mineralogy
  4. ↑ Mcbride, R. S. (1912). "The standardization of potassium permanganate solution by sodium oxalate". J. Am. Chem. Soc. 34: 393. doi:10.1021/ja02205a009.