| Themes > Science > Chemistry > Electrochemistry > Theory of Electrolytes > Units |
Because of the accumulation of historical units in this area, it is as well to keep clearly in mind which units must be used in each equation. Most equations are given in consistent units, and it is best to stick to S.I. and molecular units wherever possible, converting back to the historical units where necessary at the end of the calculation. To shoehorn ionic strength I into the S.I. system, it must be given the units mol.kg-1 rather than M . The molecular S.I. quantity is Scizi2 with units molecules.m-3, obtained by multiplying I by 2000NA = 1.2046E27 . In most equations, the dielectric constant of the solvent e must be in the S.I. units F.m-1 (farads/metre), and the value is very small, e.g. water 6.95E-10 . However sometimes it is given relative to the dielectric constant of a vacuum, 8.85 pF.m-1. In these units all dielectric constants are greater than 1, e.g. for water 78.5. The relative dielectric constant is usually symbolised er . |
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