## mean activity of an electrolyte in solution

in mass spectrometry
https://doi.org/10.1351/goldbook.M03774
Defined by the equation: $a_{\pm }=\mathrm{e}^{(\mu _{\text{B}}- \mu _{\text{B}}^{\unicode{x29B5}})\ \nu \ R\ T}$ where $$\mu _{\text{B}}$$ is the @C01032@ of the solute B in a solution containing B and other species. The nature of B must be clearly stated: it is taken as a group of ions of two kinds carrying an equal number of positive and negative charges, e.g. Na+ + NO3 or Ba2+ + 2Cl or 2Al3+ + 3SO42− . $$v$$ is the total number of ions making up the group i.e. 2, 3 and 5 respectively in the above examples. $$\mu _{\text{B}}^{\unicode{x29B5}}$$ is the @C01032@ of B in its @S05925@, usually the hypothetical ideal solution of concentration $$1\ \text{mol}\ \text{kg}^{-1}$$ and at the same temperature and pressure as the solution under consideration.