electrolyte solution

Dissolve table salt in water and something special happens that dissolving sugar does not: the solution can now carry an electric current. That is because the salt does not just spread out as whole units — it splits into charged particles, free ions drifting through the water. A solution that contains such mobile ions and therefore conducts electricity is called an electrolyte solution.

An electrolyte is a substance that breaks apart into ions when dissolved (or melted); the resulting ionic solution conducts because the positive and negative ions can move toward opposite electrodes and ferry charge. Strong electrolytes, like common salts and strong acids, dissociate almost completely; weak electrolytes, like vinegar's acetic acid, split only partly, so just a fraction of their molecules become ions at any moment.

Electrolyte solutions are everywhere it matters: the saltwater in your cells and blood that carries nerve signals, the acid in a car battery, and the conducting fluid in every wet-cell battery. Because their ions tug on one another so strongly, electrolyte solutions are markedly non-ideal — their activity coefficients drop below 1 even when dilute — so accurate work uses activities rather than raw concentrations.