$word_{count}$: 190

In aqueous electrolysis, both the solute ions and water can react at each electrode. The species with the more favourable (less negative) potential reacts preferentially, modified by overpotential. At cathode: if E($M^{n+}$) > E(H2O) = -0.83 V, the metal deposits. Active metals (Na, K, Ca, Al) have E << -0.83 V, so H2O is reduced to H2. At anode: the species with less positive oxidation potential is oxidised. In dilute NaCl: O2 at anode (from water). In concentrated NaCl: Cl2 at anode (O2 has high overpotential). In CuSO4 with inert electrodes: Cu at cathode, O2 at anode. With Cu electrodes: Cu dissolves at anode and deposits at cathode ([Cu2+] stays constant). Key rule: metals below hydrogen in the electrochemical series (Cu, Ag, Au) deposit from aqueous solution; metals above hydrogen do not (must use molten salt).