Level: advanced
Reference: Svante Arrhenius, "On the Dissociation of Substances Dissolved in Water," Zeitschrift für physikalische Chemie 1, 631-48 (1887)
Notes: Svante Arrhenius (1859-1927) is best known to chemists for his work on electrolyte solutions and kinetics. He also attempted to model the influence of atmospheric carbon dioxide on climate (a phenomenon now known as the greenhouse effect). He was awarded the Nobel Prize in chemistry in 1903.
The terminology employed by Arrhenius can be a bit confusing to a modern student of physical chemistry. Arrhenius called the quantity α the "activity coefficient," but it is not the same thing as what modern physical chemistry texts call the activity coefficient (following G. N. Lewis). To make matters more confusing, a modern physical chemist might recognize that the Arrhenius α, derived from conductance measurements, combines effects of dissociation and ionic activity in the modern sense. For weak electrolytes, α represents dissociation ratios to a good approximation, and we may neglect ionic activity coefficients. For strong electrolytes at the concentrations mentioned here, ionic activities are quite important, and they are the focus of this exercise.
Arrhenius's reported α values vary with ionic charge and molar mass in a manner similar to Debye-Hückel limiting law values of the ionic activity coefficient γ; however, quantitative agreement is not good. Solutions of strong electrolytes are just plain complicated except in the limit of very dilute solutions. For more on their complexities, especially on limitations of the notion of complete ionization, see Stephen J. Hawkes, "Salts are mostly NOT ionized," J. Chem. Educ. 73, 421-3 (1996) and Rajalakshmi Heyrovská, "Physical electrochemistry of strong electrolytes based on partial dissociation and hydration," J. Electrochem. Soc. 143, 1789-93 (1996).
Solutions: To download solutions, go to:
http://web.lemoyne.edu/giunta/classicalcs/arrstrongelec.doc
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