Electrolysis Investigation

Electrolysis Investigation

Planning

In this investigation, I will assess how changing the electric current

in the electrolysis of acidified water affects the rate at which

hydrogen gas is produced. The solution to be electrolysed is made up

using acid and water. It is of little consequence what acid is used

however in this case I will use Sulphuric acid (H2SO4).

When H2SO4 is put in water it is dissociated and forms ions:

H2SO4 → 2H (2+) + SO4 (2-)

Ions are also present from the water in the solution:

H2O → H (+) + OH (-)

During the electrolysis process, the positive hydrogen ions move

towards the cathode and the negative hydroxide and sulphate ions move

towards the anode.

At the cathode the hydrogen ions gain an electron. They are discharged

and are converted into hydrogen gas:

2H (+) + 2e (-) → H2

At the anode, the hydroxide, not the sulphate ions are discharged.

Water and oxygen gas are formed:

4OH (-) → 2 H2O + O2 + 4e (-)

The hydrogen gas can be collected and measured. The greater the volume

of hydrogen gas formed over a set period of time, the faster

electrolysis is occurring.

In the experiment there are several possible ways of changing the

electric current such as changing the voltage or the position of the

electrodes within the electrolysis cell. However, it was found from

preliminary work that the most effective way to change the current was

to change the concentration of the acid solution. The preliminary work

showed that the greater the concentration of the acid, the greater the

current. Ohm's law states that R(resistance) = V(voltage)

I (current)

Therefore, I = V

R

Therefore, if V is constant, in order to increase I, R must decrease.

Inversely, to decrease I, R must increase. The value of R depends on

how easy it is for the electric charge to pass through the conductor.

Therefore to decrease R, the passage must be made easier and to