# Charge Balance Approximation

1. Feb 14, 2014

### Qube

1. The problem statement, all variables and given/known data

Question: is the charge sum an approximation?
2. Relevant equations

E.g. consider 0.10 M $Na_{2}SO_{4}$ solution.

Charge sum appears to be 0.20 from elementary stoichiometric considerations.

3. The attempt at a solution

The charge sum, however, seems to be ignoring the auto-ionization of water, which forms two ions - hydronium and hydroxide. Am I correct? This doesn't make a significant difference for most solution considerations, right?

2. Feb 14, 2014

### Staff: Mentor

We often ignore ions present in very small concentrations, but full charge balance equation for sodium sulfate solution is

$$[Na^+] + [H^+] = 2[SO_4^{2-}] + [OH^-]$$