Electrolysis of Water

Study Notes

Water decomposes into hydrogen and oxygen gas when electric current is passed through acidified water.
The reaction can be represented as: 2H2O(l)⟶2H2(g)+O2(g)2H_2O(l) \longrightarrow 2H_2(g) + O_2(g)2H2O(l)⟶2H2(g)+O2(g)

A wide-mouthed glass bottle with a removed bottom is used, fixed on a stand in an inverted position.
A rubber cork with two holes is fitted in the neck of the bottle, with two carbon rods (or graphite rods) fixed in the holes tightly.
The glass bottle is filled two-thirds with water, and a few drops of dilute sulphuric acid are added to make water a good conductor of electricity.

Two similar test-tubes filled with water are inverted over the two carbon electrodes, keeping them initially filled with water.
The outer ends of carbon rods are connected to the two terminals (+) and (-) of a 6 volt battery by wires having a switch.
The left-side carbon rod is connected to the (+) terminal of the battery, and the right-side carbon rod is connected to the (-) terminal of the battery.
When the switch is closed, gas bubbles are formed at both carbon electrodes.

Gas bubbles formed at the left-side carbon electrode (connected to the (+) terminal) are of oxygen, which can be tested by bringing a glowing splinter near the mouth of the test-tube, causing it to burst into flame.
Gas bubbles formed at the right-side carbon electrode (connected to the (-) terminal) are of hydrogen, which can be tested by bringing a burning candle near the mouth of the test-tube, causing it to extinguish.

When electricity is passed through water, it decomposes to give hydrogen and oxygen gas.
The volume of hydrogen gas collected at the cathode is double the volume of oxygen gas collected at the anode, which is in accordance with the formula of water, H2O.