Натрий оксалат

Описание

Sodium oxalate, or disodium oxalate, is the 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 ultraalkaline pegmatites.

Химические свойства

White, crystalline powder. Soluble in water; insolu- ble in alcohol.

Физические свойства

White crystalline powder; density 2.34 g/cm³; decomposes around 250° C; sparingly soluble in water, 3.7 g/100 mL at room temperature; moderately soluble in boiling water, about 6.25 g/100 mL; the aqueous solution is practically neutral; insoluble in alcohol.

Использование

Sodium Oxalate is obtained in such high purity and is so stable that it is used as a titrimetric standard.

Подготовка

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.

Определение

ChEBI: An organic sodium salt consisting of sodium and oxalate ions in a 2:1 ratio.

Реакции

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:
5Na₂C₂O₄ + 2KMnO₄ + 8H₂SO₄ → K₂SO₄ + 2MnSO₄ + 10CO₂ + 8H₂O.

Общее описание

Odorless white solid. Sinks and mixes slowly with water.

Профиль реактивности

Disodium oxalate gives basic aqueous solutions. Neutralizes acids in exothermic reactions. Can serve as a reducing agent in reactions that generate carbon dioxide.

Опасность

Toxic by ingestion.

Угроза здоровью

Inhalation or ingestion causes pain in throat, esophagus, and stomach; mucous membranes turn white; other symptoms include vomiting, severe purging, weak pulse, cardiovascular collapse, neuromuscular symptoms, and kidney damage. Contact with eyes or skin causes irritation.

Токсикология

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.

Методы очистки

It crystallises from hot water (16mL/g) by cooling to 0o. Before use as a volumetric standard, analytical grade quality sodium oxalate should be dried for 2hours at 120o and allowed to cool in a desiccator. [Beilstein 2 IV 1819.]