Sodium hydrogenoxalate

Properties

Hydrates

The compound is commonly encountered as the anhydrous form or as the monohydrate NaHC₂O₄·H₂O. Both are colorless crystalline solids at ambient temperature.

The monohydrate can be obtained by evaporating a solution of the compound at room temperature.

The crystal structure of NaHC₂O₄·H₂O is triclinic normal (pinacoidal, space group P1). The lattice parameters are a = 650.3 pm, b = 667.3 pm, c = 569.8 pm, α = 85.04°, β = 110.00°, γ = 105.02°, and Z = 2. The hydrogen oxalate ions are linked end to end in infinite chains by hydrogen bonds (257.1 pm). The chains are cross linked to form layers by both O−H···O bonds from the water molecules (280.8 pm, 282.6 pm) and by ionic bonds Na⁺···O. These layers are in turn held together by Na⁺···O bonds. The oxalate group is non-planar with an angle of twist about the C−C bond of 12.9°.

Reactions

Upon being heated, sodium hydrogenoxalate converts to oxalic acid and sodium oxalate, the latter of which decomposes into sodium carbonate and carbon monoxide.

2 NaHC₂O₄ → Na₂C₂O₄ + H₂C₂O₄

Na₂C₂O₄ → Na₂CO₃ + CO