Water (as molecules) is decomposed by direct current to hydrogen and oxygen. Hydrogen evolves as gas bubbles from the surface of the cathode (- electrode), the bubbles of oxygen are released from the anode (+ electrode):
1) ON CATHODE (-): water molecules are reduced:
4H2O(l) + 4e- → 2H2(g) + 4OH-(aq)
2) ON ANODE (+): water molecules are oxidized:
2H2O(l) – 4e- → O2(g) + 4H+(aq)
According to the equations above, hydrogen and oxygen are produced in molar ratio 2:1, thus, also in volume ratio 2:1.
Potassium hydroxide (electrolyte:~15 % solution of KOH) was added to the water for increased conductivity. Nickel plates were used as the electrodes.
1) The hydrogen evolved from the cathode was passed into “bubble liquid”, the obtained hydrogen foam was ignited.
2) The oxygen was passed into a test tube and tested with a glowing wooden splint.
1) Identification of hydrogen, combustion of hydrogen in air:
2H2(g) + O2(g) → 2H2O(g)
2) Identification of oxygen, combustion of coal (carbon) in oxygen:
C(s) + O2(g) → CO2(g)