5.4 Electrolysis Flashcards
(12 cards)
What is electrolysis
The breaking down of a compound using electricity
What happens to the substance to be broken down
It is connected into a circuit with a cell or battery
Name the electrodes
Positive electrode = anode
Negative electrode = cathode
What must the electrodes be made of
They must be made of a solid that conducts electricity but is inert (unreactive)
Usually graphite (cheap) or platinum (expensive)
What is the electrolyte
The substance to be broken down
What must the electrolyte be made of
Ionic compounds that are molten or dissolved so that the ions are free to move and carry charge
Electrolyte names
Positive ions are called cations because they are attracted to the cathode
Negative ions are called anions because they are attracted to the anode
What does electrolysis of a molten ionic compound produce
Its elements
What can water molecules be broken apart to form
H+ and OH- ions
Ions in water - rules at the anode
If a halide ion (Cl- / Br- / I-) is present, that element is produced as per normal: e.g. 2Br- —> Br2 + 2e-
Otherwise, O2 and H2O are produced according to the following half equation: 4OH- —> O2 + 2H2O + 4e-
Ions in water - rules at the cathode
If the metal is less reactive than hydrogen, that element produced is as per normal: e.g. Cu2+ + 2e- —> Cu
Otherwise, H2 is according to the following half equation: 2H+ + 2e- —> H2
Ions in water - rules for ions that did not react
Whichever ions did not react remain leftover in the solution as a third product
