Читать книгу Geochemistry - William M. White - Страница 140

There is an additional condition that electrolyte solutions must meet: electrical neutrality. Thus, the sum of the positive charges in solutions must equal the sum of the negative ones, or:

(3.99)

While this presents some experimental obstacles, for example, we cannot add only Na⁺ ion to an aqueous solution while holding other compositional parameters constant; it also allows placement of an additional mathematical constraint on the solution. It

is often convenient to rearrange eqn. 3.99 so as to place anions and cations on different sides of the equation:

(3.100)

As an example, consider water in equilibrium with atmospheric CO₂ and containing no other species. The charge balance equation in this case is:

As Example 3.10 illustrates, the electrical neutrality constraint can prove extremely useful.