C6- Electrolysis Flashcards
Electrolysis
Breaking down ionic compounds using electricity
Electrolyte
The ionic compound broken down (solution)
Why cant the electrolyte be a solid?
This is because the ions in a solid are not free to move due to the strong electrostatic forces of attraction ( and if not free then electricity doesn’t flow)
Whats the cathode?
The negative electrode
Whats the anode?
The positive electrode
What are the electrodes made off?
Carbon
What happens at the anode?
Oxidations
What happens at the cathode?
Reduction
Whats aluminium useful for?
Pans, cooking foil, aeroplanes, drink cans, car bodies, bicycle frames…
Whats the name of Aluminium’s metal ore?
Bauxite
Whats the aluminium oxide mixed with for electrolysis?
Molten cryolite
Why is aluminium oxide mixed with molten cryolite?
To lower the melting point and this will reduce the amount of energy needed and save money
Whats forms at the cathode when Aluminium is electrolysed?
Aluminium
What forms at the Anode when aluminium is electrolysed ?
Oxygen
Whats the half equation for the reaction at the Cathode ( electrolysis of aluminium)?
AL3+(L)+ 3e- —— -> AL(L)
Whats the half equation for the reaction at the Anode ( electrolysis of aluminium)?
2O2- (L) ——-> O2 (g) + 4e-
Why do the carbon anodes have to be replaced regularly (electrolysis of aluminium)
Because they regularly burn away as the oxygen reacts with the carbon anodes forming carbon dioxide gas
During electrolysis of aqueous solutions where the H+ and OH- ions come from?
When the water breaks down
During electrolysis of aqueous solutions what forms at the cathode?
The less reactive element between the positive ions ( either hydrogen or the metal) you use the reactivity series
During electrolysis of aqueous solutions what forms at the anode?
OH- (hydroxide) is given off unless the electrolyte id a solution of a halide (group 7) if so a halogen is given off
Halide> hydroxide> all other negative charged ions
What is brine?
concentrated sodium chloride solution
What is the word equation for the electrolysis of brine (sodium chloride solution)?
Sodium chloride solution —> hydrogen gas+ chlorine gas+ sodium hydroxide solution
What forms at the cathode during the electrolysis of brine?
Hydrogen (H+) ions gain 1 electron (reduced). The hydrogen atoms bond together in pairs and give off hydrogen gas
What forms at the anode during the electrolysis of brine?
Chlorine atoms lose 1 electron (oxidised). The chlorine atoms bind together in pairs and give ofd chlorine gas
Whats the half equation at the cathode during the electrolysis of brine (sodium chloride solution)?
2H+(aq) + 2e- ——> H2(little 2 not a charge)
Whats the half equation at the anode during the electrolysis of brine (sodium chloride solution)?
2CL- (aq) —–> CL2 +2e-
Whats the lab test for chlorine gas ?
Bleaches damp litmus paper white
Whats the lab test for hydrogen gas?
Squeaky ‘pop’ with lighted splint
Whats the lab test for oxygen ?
Relights glowing splint
Name 3 control variables/ precautions when investigating the electrolysis of a solution?
- don’t let the 2 electrodes touch each other as a short circuit would be produce pd
- wear gloves and eye protection
- use a lid to ensure the gas doesn’t escape
- pay close attention to gases being produces as the volume of them will be very small
What are the observations and element formed at the Anode during the electrolysis of copper (II) chloride?
Bubbles, chlorine
What are the observations and element formed at the Cathode during the electrolysis of copper (II) chloride?
Colour change, copper
What are the observations and element formed at the Anode during the electrolysis of copper (II) sulfate?
Bubbles ,oxygen
What are the observations and element formed at the Cathode during the electrolysis of copper (II) sulphate?
Colour change, copper
What are the observations and element formed at the Anode during the electrolysis of sodium chloride?
Bubbles, chlorine
What are the observations and element formed at the Cathode during the electrolysis of sodium chloride?
Bubbles, hydrogen
What are the observations and element formed at the Anode during the electrolysis of sodium sulfate?
Bubbles, oxygen
What are the observations and element formed at the Cathode during the electrolysis of sodium sulfate ?
Bubble, hydrogen
Explain why carbon electrodes can conducted electricty
It has delocolised electrons that are free to move throughout the structure
Whats the half equation at cathode in the electrolysis of lead bromide?
Pb—–> Pb2+ + 2e-
Whats the half equation at anode in the electrolysis of lead bromide?
2Br- + 2e- ——–> 2Br-
