Given the ion C2O4-2, what species would you expect to form with each of the following ions? A. K+
B. Cu2+
C. Bi3+
D. Pb4+
E. NH4+
F. H+

A. K₂C₂O₄          Potassium oxalate

B. CuC₂O₄          Copper oxalate

C. Bi₂(C₂O₄)₃         Bismuth (III) oxalate

D. Pb(C₂O₄)₂         Lead (IV) oxalate

E. (NH₄)₂C₂O₄       Ammonium oxalate

F. HC₂O₄⁻             Acid oxalate

Explanation:

C₂O₄⁻²  → oxalate anion

This is the conjugate base from the H₂C₂O₄ which is the oxalic acid. A weak dyprotic acid that can release 2 protons.

A. 2K⁺  +  C₂O₄⁻²  → K₂C₂O₄          Potassium oxalate

It can be formed by the neutralization of the acid with the base

H₂C₂O₄  + 2KOH  → K₂C₂O₄  +  2H₂O

B. Cu²⁺ +  C₂O₄⁻²   ⇄  CuC₂O₄  ↓

This is a precipitate.

C.  2Bi³⁺  +  3C₂O₄⁻²   ⇄  Bi₂(C₂O₄)₃  ↓

This is a precipitate.

D.  Pb⁴⁺ +  2C₂O₄⁻²   ⇄  Pb(C₂O₄)₂  ↓

This is a precipitate.

E. 2NH₄⁺  +  C₂O₄⁻²   ⇄  (NH₄)₂C₂O₄  ↓

This is a precipitate.

F. This is the conjugate strong base, for the weak acid

H⁺  +  C₂O₄⁻²   ⇄  HC₂O₄⁻

HC₂O₄⁻  + H₂O  ⇄  C₂O₄⁻²  +  H₃O⁺    Ka

HC₂O₄⁻  + H₂O  ⇄  H₂C₂O₄  +  OH⁻    Kb

HC₂O₄⁻  is an amphoteric compound

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