What is a cathode ?
Negative electrode
What is an anode ?
Positive electrode
A solution of copper sulfate is being electrolysed.
What elements would be discharged at each electrode ?
anode: oxygen (OH-)
cathode: copper (Cu2+)
What is the order of discharge at the anode ?
halogens > hydroxides > all other negative ions
Write the half equation for the discharge of copper at a cathode.
Cu2+ + 2e- –> Cu
Write the half equation for the discharge of chlorine at the anode.
Cl- –> Cl + e-
What does ‘OIL RIG’ stand for ?
Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons)
If chlorine is discharged at the anode, has it been reduced or oxidised ?
oxidised (loses one electron)
If copper (II) is discharged at the cathode, has it been reduced or oxidised ?
reduced (gains 2 electrons)
What ore do you get aluminium oxide (Al2O3) from ?
Bauxite
How is aluminium extracted via electrolysis ?
- aluminium oxide extracted from bauxite
- aluminium oxide heated with molten cryolite to reduce energy costs (can be electrolysed at 850’C instead of 1500’C)
- at cathode, aluminium discharged
- at anode, oxygen gas discharged
- oxygen reacts with hot carbon electrodes to give carbon dioxide, which eventually destroys the electrodes
- electrodes are regularly replaced
What is brine ?
conc. sodium chloride solution
Give the products of the electrolysis of brine.
- sodium hydroxide solution
- chlorine gas (discharged at anode)
- hydrogen gas (discharged at cathode)
If either hydrogen or another positive ion may be discharged as its element at the cathode, which will be discharged ?
Hydrogen (gas)
