According to the Lux-Flood acid-base theory, it was a revival of the oxygen theory of acids and bases proposed by the German chemist Hermann Lux in 1939 and further improved by Håkon Flood circa 1947. It is still used in modern geochemistry and for the electrochemistry of molten salts.
"An acid is an oxide ion (O2−) acceptor and a base is an oxide ion donor."
According to the concept, a base is any material which gives up oxide ions and an acid is any material which gains oxide ions. Some typical reactions include the following:
- Base ↔ Acid + O2−
- SO42− ↔ SO3 + O2−
- CaO ↔ Ca2+ + O2−
Hence, according to this concept, an acid is an oxide or O2− acceptor and a base is an oxide or O2− donor.
Applications in High-Temperature Chemistry
This view is particularly useful to high temperature chemistry, as in the fields of ceramics and metallurgy. For example, consider the following reactions involving basic oxides (CaO, PbO) and acidic oxides (SO3, SiO2) to form salts:
- CaO + SiO2 → CaSiO3
- PbO + SO3 → PbSO4
Amphoteric Substances
Also according to Lux-Flood acid-base theory, amphoteric substances are those which show both a tendency to take up or give up oxide ions depending upon the circumstances. For example, ZnO acting as an acid:
Na2O + ZnO → 2Na+ + ZnO22−
Extension of the Concept
The oxide transfer picture due to Lux can be extended to include the transfer of any anion, such as halides or sulphides:
3NaF + AlF3 —high temperature→ 3Na+ + AlF63−
Limitations: The limitations of this concept are obvious. This view can be reduced to one part of the more general theories of Lewis and Usanovich.
Related topics
Brønsted–Lowry Theory of Acids and Bases
Arrhenius Theory of Acids and Bases
Lewis Theory of Acids and Bases
Hard Soft Acid Base Principle