This table gives the molar (equivalent) conductivity λ for common ions at infinite dilution. All values refer to aqueous solutions at 25 °C. It also lists the diffusion coefficient D of the ion in dilute aqueous solution, which is related to λ through the equation
D = (RT/F2)(λ/|z|)
where R is the molar gas constant, T the temperature, F the Faraday constant, and z the charge on the ion. The variation with temperature is fairly sharp; for typical ions, λ and D increase by 2 to 3% per degree as the temperature increases from 25 °C. Column definitions for the table are as follows.
Column heading | Definition |
Mol. form. | Molecular formula of ion; ions are listed alphabetically by molecular formula; in the table, values are categorized in the following order: Inorganic Cations, Inorganic Anions, Organic Cations, Organic Anions |
Λ± | Molar (equivalent) ionic conductivity per unit charge, in units of 10-4 m2 S mol-1 |
D | Diffusion coefficient, in units of 10-5 cm2 s-1 |
The diffusion coefficient for a salt, Dsalt, may be calculated from the D+ and D– values of the constituent ions by the relation
For solutions of simple, pure electrolytes (one positive and one negative ionic species), such as NaCl, equivalent ionic conductivity Λ°, which is the molar conductivity per unit concentration of charge, is defined as
Λ° = Λ+ + Λ–
where Λ+ and Λ– are equivalent ionic conductivities of the cation and anion. The more general formula is
Λ° = ν+Λ+ + ν−Λ–
where ν+ and ν− refer to the number of moles of cations and anions, respectively, to which one mole of the electrolyte gives rise in solution.
Mol. form. | Λ±/10–4 m2 S mol–1 | D/10–5 cm2 s–1 |
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Inorganic Cations | ||
Ag+ | 61.9 | 1.648 |
1/3Al3+ | 61 | 0.541 |
1/2Ba2+ | 63.6 | 0.847 |
1/2Be2+ | 45 | 0.599 |
1/2Ca2+ | 59.47 | 0.792 |
1/2Cd2+ | 54 | 0.719 |
1/3Ce3+ | 69.8 | 0.620 |
1/2Co2+ | 55 | 0.732 |
1/3[Co(NH3)6]3+ | 101.9 | 0.904 |
1/3[Co(en)3]3+* | 74.7 | 0.663 |
1/6[Co2(trien)3]6+** | 69 | 0.306 |
1/3Cr3+ | 67 | 0.595 |
Cs+ | 77.2 | 2.056 |
1/2Cu2+ | 53.6 | 0.714 |
D+ | 249.9 | 6.655 |
1/3Dy3+ | 65.6 | 0.582 |
1/3Er3+ | 65.9 | 0.585 |
1/3Eu3+ | 67.8 | 0.602 |
1/2Fe2+ | 54 | 0.719 |
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