What is Lux-Flood Theory for Acids and Bases ?

Lux-Flood Theory

Lux-Flood Theory was introduced by Lux (1929) and supported by Flood (1947). This theory was related to acid-base reactions with respect to the oxide ion. According to the Lux-Flood theory, an acid is the oxide-ion acceptor while a base is the oxide-ion donor.
Examples:
MgO + SiO₂ → MgSiO₃
CaO + SO₃ → CaSO₄

In the above reactions both MgO and CaO are the oxide ion donor and hence act as bases, whereas SiO₂ and SO₃ are the oxide-ion acceptor and hence act as acids.

Other examples of Lux-Flood Theory are-
SiO₂, SO₃, CO₂ etc. are Lux Flood acids.
CaO, MgO, PbO, Al₂O₃ etc. are Lux Flood bases.
ZnO + O^-2 ⟶ ZnO₂^-2
(Acid)
ZnO + O^-2 ⟶ Zn⁺² + O₂^-2
(Base)
ZnO is the amphoteric oxide.
According to Lux-Flood theory, Xenon fluorides accept oxide ions from other compounds.
XeF₆ + POF₃ → XeOF₄ + PF₅

This theory is particularly applicable to reactions which take place at high temperature – like metallurgical operations, manufacture of ceramics and glass.

Limitations of Lux-Flood Theory

1. The theory is applicable to molten oxides only.
2. Base must contain oxide ion and acid must have to accept oxide ions.
3. It fails to explain reaction without metal ions.