C6 : Electrolysis Flashcards
What will the electrolysis of AQUEOUS NaCl produce ?
Sodium hydroxide
Chlorine
HYDROGEN
What happens if metal ions in reaction are lower than H+?
Ions lower in reactivity mean EASIER TO DISCHARGE
so that gets discharged instead of H+
What ions are discharged easier than OH- ions ?
HALIDE IONS (G7)
How can IONIC compounds conduct electricity ??
Ions can conduct when MOLTEN/AQUEOUS
bc the ions are MOBILE to carry charge
What happens to oxygen and aluminium in the electrolysis of aluminium ? Half equations?
Oxygen LOSE electrons - gain O2
2O^2- - 4e- —> o2
Aluminium GAINS electrons - lose 02
Al^3+ + 3e- —> Al
why is a mixture of cryolite and aluminium oxide used?
to lower MP, reducing energy needed to extract aluminium
why does the positive electrode have to be replaced at regular intervals? (4)
- electrode is made from carbon
- 02 is produced at anode (+)
- reacts with anode to form CO2
- needs to be replaced, as carbon is being lost
why is aluminium expensive
- requires a lot of energy to extract
- requires mining/ getting rid of waste solution
why is aluminium formed at the cathode (-)?
Al ions are +.
Al ions are attracted to negative electrode.
Al gains electrons and is REDUCED!
Al3+ + 3e- –> Al
why does CU2+ form a solid at negative electrode?
cu2+ gains 2 electrons to form copper
cu2+ +2e- –» Cu
eqn for molten sodium chloride when electrolysed?
2NaCl –> 2Na + Cl2
equn for molten potassium bromide when electrolysed?
2KBr –> 2K + BR2
half equation if hydroxide ions are discharged?
4OH– ⟶ O2 + 2H2O + 4e–
required practical: electrolysis
- Add the aqueous solution to the beaker
- Add two graphite rods as the electrodes/ put test tubes on electrodes and connect this to a power pack or battery
- Turn on the power pack or battery and allow electrolysis to take place
- Record the results in a suitable table and repeat for another solution, checking the electrodes in between runs to see if any metal has been deposited
- The gases produced can be collected in the test tubes to be tested later
