Sodium oxalate

Disodium oxalate
IUPAC name Disodium oxalate
Other names Oxalic acid, disodium salt Sodium ethanedioate
Identifiers
CAS number	62-76-0 Y
PubChem	6125
ChEMBL	CHEMBL182928 N
RTECS number	K11750000
Properties
Molecular formula	Na2C2O4
Molar mass	134.00 g mol−1
Density	2.34 g cm−3
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
N (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Disodium oxalate, often called simply sodium oxalate, is a sodium salt of oxalic acid with the molecular 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 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 manganate(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]

5H₂C₂O₄ + 2KMnO₄ + 3H₂SO₄ → K₂SO₄ + 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://rruff.geo.arizona.edu/doclib/hom/natroxalate.pdf Handbook of Mineralogy
2. ^ Mcbride, R. S. (1912). "The standardization of potassium permanganate solution by sodium oxalate". J. Am. Chem. Soc. 34: 393. doi:10.1021/ja02205a009.