Electrolysis of sodium chloride solution. Footage of electrodes in a beaker of water (H2O) containing dissolved salt (sodium chloride, NaCl). The power to the electrodes is turned on, and the light bulb at upper left comes on, indicating that electrical current is flowing through the liquid, between the electrodes. The electrode with the positive polarity (red) is the anode. The other one (black) is the cathode. Electrolysis of ionic solutions causes the ions to be deposited at electrodes of the opposite polarity. In this case, the negative chloride ions (Cl-) are deposited at the anode, forming bubbles of chlorine gas (Cl2). Hydrogen gas (H2) is formed at the cathode. Sodium hydroxide (NaOH) is formed in solution. The chlorine gas is more visible here because it is coloured, as opposed to the colourless hydrogen gas.