The Acidic Environment - Acids Throughout History

Outline the historical development of ideas about acids including those of:

Operational definitions: Definitions based entirely on particular observations.
The earliest concepts of acids were operational definitions, based on observations such as:
- Sourness when tasted.
- Ability to change the colours of indicators.
Conceptual definitions: Definitions that attempt to explain observations.
As the field of chemistry developed, concepts of acids began to expand into conceptual definitions.

Year	Individual	Acid theory	Evidence / Details
1766	Antoine Lavoisier	Acids were substances that contained oxygen	Based on the observation that non-metal oxides produced acidic solutions Later disproved, as many basic substances were found to contain oxygen, and some acidic substances were found not to contain oxygen
1810	Humphry Davy	Acids were substances that contained hydrogen that could be replaced totally or partly by metals	Based on the observation that when acids reacted with metals, the metal appeared to replace the hydrogen in the acid, causing hydrogen gas to be evolved
1884	Svante Arrhenius	Acids were substances that ionised in solution to produce hydrogen ions	Acids were strong if they ionised almost completely, and weak if they ionised only slightly This ignored the role of the solvents