Lead(II) oxalate explained

Lead(II) oxalate is an organic compound with the formula PbC₂O₄. It is naturally found as a heavy white solid.^[1]

Preparation

This compound is commercially available. It may be prepared by the metathesis reaction between lead(II) nitrate and sodium oxalate:^[2]

Pb²⁺(aq) + C₂O₄^2- → PbC₂O₄ (s)

A dihydrate may be formed with water solutions. But the dihydrate dehydrates in air:

(PbC₂O₄•2H₂O (s) → (PbC₂O₄ (s) + 2H₂O (g)

The trihydrate (PbC₂O₄•3H₂O) can be made by reacting a solution of lead(II) carbonate in perchloric acid with oxalylhydroxamic acid.

Properties

As well as an anhydrous form, a monohydrate (PbC₂O₄•H₂O), a dihydrate (PbC₂O₄•2H₂O) and a trihydrate (PbC₂O₄•3H₂O) are known. The dihydrate is from the orthorhombic crystal system, with space group Pnam (number 62), with unit cell dimensions: a = 9.053 Å b = 8.036 Å and c = 7.834 Å. The unit cell volume is 569.8 ų with four formula per cell, giving a density of 3.860 g/cm^3[3]

The trihydrate has triclinic crystals with space group P and unit cell dimensions and angles: a = 6.008 Å, b=6.671 Å, c=8.493 Å, α=74.70°, β=74.33°, and γ=80.98°. The unit cell volume is 314.41 Å³ with two formula per unit cell. Density is 3.69 g/cm³.^[4]

Solubility

Lead(II) oxalate is insoluble in water. Its solubility is increased in presence of excess oxalate anions, due to the formation of the Pb(C₂O₄)₂^2- complex ion.^[5]

Notes and References

1. "Lead Oxalate". American Elements: The World's Manufacturer of Engineered & Advanced Materials http://www.americanelements.com/pboxl.html.
2. Grases, F. . Studies on Lead Oxalate Crystalline Growth . 10.1006/jcis.1993.1035 . Journal of Colloid and Interface Science . 155 . 265–270 . 1993 . Ruiz . J. . Costa-Bauzá . A. . 2.
3. Boldyreva . E. V. . Naumov . D. Y. . Podberezskaya . N. V. . Virovets . A. V. . Structure of lead(II) oxalate dihydrate . Acta Crystallographica Section C: Crystal Structure Communications . 15 November 1993 . 49 . 11 . 1882–1884 . 10.1107/S0108270193004652.
4. Sheng-Hua . Huang . Ru-Ji . Wang . Mak . Thomas C. W. . Crystal structures of isomorphous cadmium(II) and lead(II) oxalate trihydrates . Journal of Crystallographic and Spectroscopic Research . April 1990 . 20 . 2 . 99–104 . 10.1007/BF01160959.
5. Kolthoff, I.M. . The Solubility of lead Sulfate and of Lead Oxalate in Various Media . 10.1021/j150419a004 . 1942 . Perlich . R. W. . Weiblen . D. . Journal of Physical Chemistry . 46 . 5 . 561.