QuestionElectrochemistry / activity coefficients
The mean ionic activity co-efficient is denoted as γ±, while that of cation and anion are denoted as γ₊ and γ₋, respectively. The correct relation among them will be: (Given that ν₊ and ν₋ are the number of cations and the anions respectively in the molecular formula of the compound)
- (a) \(\gamma_\pm = \frac{1}{\nu_+ + \nu_-}(\gamma_+ + \gamma_-)\)
- (b) \(\gamma_\pm = (\gamma_+^{\nu_+}\gamma_-^{\nu_-})^{1/(\nu_+ + \nu_-)}\)
- (c) \(\gamma_\pm = (\gamma_+^{\nu_-}\gamma_-^{\nu_+})^{1/(\nu_+ + \nu_-)}\)
- (d) \(\gamma_\pm = \frac{1}{\nu_+ + \nu_-}(\nu_+\gamma_+ + \nu_-\gamma_-)\)
Answer: (b) \(\gamma_\pm = (\gamma_+^{\nu_+}\gamma_-^{\nu_-})^{1/(\nu_+ + \nu_-)}\)
Mean ionic activity coefficient is the geometric mean: γ± = (γ₊^ν₊ γ₋^ν₋)^(1/(ν₊ + ν₋)) → (b). Example: for CaCl₂, γ±³ = γ₊γ₋².