Quimica analítica

Assuntos Gerais

Quim. Nova, Vol. 30, No. 1, 232-239, 2007
DE SVANTE ARRHENIUS AO PEAGÂMETRO DIGITAL: 100 ANOS DE MEDIDA DE ACIDEZ
Michelle da Silva Gama e Júlio Carlos Afonso*
Departamento de Química Analítica, Instituto de Química, Universidade Federal do Rio de Janeiro, CT, Bloco A, CP 68563,
21949-900 Rio de Janeiro - RJ, Brasil
Recebido em 6/4/05; aceito em 13/1/06; publicado na web em 11/8/06

FROM SVANTE ARRHENIUS TO THE DIGITAL pH METER: A CENTURY OF ACIDITY MEASUREMENT. This work describes the establishment of the concept of pH and the evolution of its measurement. The origin of the pH definition can be found in the development of the chemistry of aqueous solutions during the XIXth century. The electrolytic dissociation theory by Svante Arrhenius played a central role. After the proposal of the pH scale by Sörensen, many years were necessary for the acceptance of this new parameter among chemists in general. Its importance was first recognized in biochemistry and related areas. Twenty years after, its importance had been recognized in many industrial and laboratorial practices. The previous methods were based on colorimetric and electrometric methods, but both suffered from many problems. Acceptance of pH in Chemistry was only possible after the development of experimental trustable measurements. The invention of the pH meter was the primordial step.
Keywords: pH; pH meter; acidity measurement.

O CONHECIMENTO DA QUÍMICA EM SOLUÇÃO
AQUOSA NA SEGUNDA METADE DO SÉCULO XIX
Na segunda metade do século XIX, muitos conceitos físicoquímicos estavam sendo estabelecidos1-5. Na década de 1860, Cato
M. Guldberg (1836-1902) e Peter Waage (1833-1900) formularam a lei da ação das massas. Em 1877, Wilhelm Pfeffer (1845-1920) produziu a primeira membrana semipermeável, com a qual descobriu a proporcionalidade entre pressão osmótica e concentração da solução. François-Marie Raoult (1830-1901) publicou em 1883 seus estudos sobre abaixamento do