- раздел Образование, Part One THE PREDICATE The Subject Of Acids And Bases Has Long Been One Of The Most Controversial In...
The subject of acids and bases has long been one of the most controversial in chcmistry, and led to the development of an interesting series of theories.
In the 17th century, during the infancy of experimental chcmistry, acids and bases were defined or described on the basis of dicir behaviour. Tlius, bases were substanccs that neutralized acids, turned plant dyes blue, had a bitter taste, and had a smooth or slippery feeling to the skin.
In the 18th century, following the discovery of oxygen by Joseph Priestley, Lavoisier advanced the idea that oxygen was the acidifying principle of all acids. Thereafter, the experimental approach was largely abandoned and emphasis was placed on the composition of substanccs instead of the phcnomcnological properties. The development of the hydrogen theory of acidity and Faraday's studies of electrolytic conductancc in the early 19th ccntury led logically to the water-ion theory proposed by Arrhcnius. By this conccpt a base may be defined as any hydroxy compound which gives hydroxyl ions in water solution. Neutralization then involves the combination of hydroxyl ions with hydrogen formed by the acid, producing water and incidentally a salt. The role of solvent as an ionizing medium for acid-base reactions was emphasized. Although the theory under consideration was very useful and adequate for many reactions in aqueous solution, its many limitations soon bccamc apparent. The theory includes basic substanccs that arc not hydroxy compounds, does not provide for the amphotcrism exhibited by many oxides and salts, and limits the field of acid-basc reactions to aqueous solutions in spite of many known typical neutralization reactions in non-aqucous solutions.
These objections led to more or less conflicting theories: the protonic theory advanced by Bronstcd and Lowry in 1923 and the older solvent system advanced by Franklin in 1905 and later extended. In terms of the $ then popular protonic conccpt, a base is any substancc, molcculc, or ion, which accepts a proton.
