Lux-Flood Concept of Acids and Bases

 

Hermann Lux (1904-1999), a renounced inorganic chemist from Germany put forward his own theory of acids and bases with the help of Håkon Flood (1905-2001), another prominent inorganic chemist from Norway.

Lux and Flood proposed a concept of acids and base in terms of oxide (O^2-) ion transfer. Therefore the theory can be simplified as

Base ⇋ O^2- + Acid (conjugate)

So from this theory we can conclude that acids are usually oxide ion acceptors while bases are donors. A typical acid-base interaction in this concept looks like

CaO + SiO₂ ⇋ CaSiO₃

PbO + SO₃ ⇋ PbSO₄

The non-metal oxides are usually acidic therefore SiO₂ and SO₃ are acids and metallic oxides such as CaO and PbO are bases in the abovementioned reactions.

In this concept the properties of amphoteric oxides are explained. Amphoteric oxides are having both the tendencies to accept and donate oxide ions. The examples are

ZnO ⇋ Zn²⁺+ O^2-

ZnO+O^2- ⇋ ZnO₂^2-

Xenon fluorides are well known Lux-Flood acids. Xenon fluorides are good oxide acceptors and they can fluoridate the oxide donors. The relative acidity of xenon fluorides are

XeF₆ >XeO₂F₄ > XeO₃F₃ > XeO₄ > XeF₄ > XeO₂F₂ > XeO₃> XeF₂  

XeF₆ + H₂O → XeOF₄ + 2HF

XeOF₄ +XeO₃→2Xe₂F₂

This system proves highly valuable for managing anhydrous reactions within fused oxide melts, as well as other high-temperature reactions encountered in metallurgy and ceramics. The theory underlying this approach exhibits an inverse relationship to aqueous chemistry. Lux-Flood acids, which are oxides, react with water, yielding bases in water. Conversely, Lux-Flood bases react with water, producing acids.

Na₂O + H₂O → 2NaOH

P₄O₁₀ + 6H₂O → 4H₃PO₄

Limitations of this Concept

1) This theory only discusses about metal oxides, so the base must contain an oxygen and acid must accept it. Therefore this theory does not work for other acids and bases that does not go through with oxygen donation or acceptance.

2) This theory also does not explain non metal bases.

Reference

1) Concise inorganic chemistry by J. D. Lee.

2) Inorganic Chemistry by James E. Huheey, Ellen A Keither, Richard L. Keither, Okhil K. Medhi.