electrolytic conduction

Meaning: Electrolytic conduction is current carried by ions drifting through a solution or molten salt. Cations move toward the negative electrode and anions toward the positive electrode. Both add to the current, because opposite charges moving in opposite directions give conventional current in the same direction. Conductivity generally rises with ion concentration and ion charge. Pure water conducts poorly because it has very few ions. Heating an electrolyte generally lowers its resistance, since the solution becomes less viscous and ions move faster. Metals behave the opposite way: their resistance rises with temperature. At the electrodes, charge passes between ions and the wire through redox reactions.

Equation: I = ΔQ/Δt = V/R, where I is current (A), ΔQ is the charge crossing a cross-section (C), Δt is time (s), V is potential difference (V), and R is resistance (Ω). In a solution, ΔQ is the sum of the charge carried by cations and by anions.

On the MCAT: Passages describe salt solutions between electrodes, salt bridges in galvanic cells, or ion flow along a neuron. You may predict that adding salt lowers resistance. You may also use R = ρL/A to see that a longer or narrower solution path raises resistance.

Common confusion: Students picture electrons moving through the solution. Electrons move only in the external wire. In the solution, ions carry the charge. A second error is applying the metal temperature trend to electrolytes.