Calculate the volume of hydrogen gas at rtp liberated at the cathode in the electrolysis of acidified water by 18 moles of electrons.(One mole of any gas at rtp occupies a volume of 24 dm^3).
At the cathode the positive H+ ions accept an electron and are converted to H; as hydrogen is not stable as an individual atom, it immediately combines with another H atom to form the stable H2 molecule.
For the formation of each H2 molecule we need 2 electrons.
18 moles of electrons can help convert a quantity of H+ ions equal to 18/2 = 9 moles. The 9 moles of hydrogen gas that are formed due to the 18 moles of electrons occupy a volume equal to 9 times the volume occupied by a single mole of hydrogen gas.
As one mole of any gas at rtp occupies 24 dm^3, 9 moles of hydrogen occupies 9*24 = 216 dm^3 of volume.
The volume of hydrogen gas liberated at rtp due to 18 moles of electrons is 216 dm^3.