Section 3 - Chemical changes - Electrolysis and electrolysis of copper sulfate Flashcards
What is electrolysis?
The breaking down of a substance using electricity
What is an electrolyte?
A molten or dissolved ionic compound
What is oxidation and reduction?
Oxidation - loss of electrons
Reduction - gain of electrons
OILRIG
What are positive ions called and which electrode do they move towards in the electrolyte? What happens to them here?
Positive ions called cations in electrolyte move towards negative electrode called cathode and are reduced
What are negative ions called and which electrode do they move towards in the electrolyte? What happens to them here?
Negative ions called anions in electrolyte move towards positive electrode called anode and are oxidised
How is a flow of charge created through the electrolyte?
Cations gain and anions lose electrons which creates flow
What do half equations show?
How electrons are transferred during reactions and what happens at each electrode during electrolysis
What is an electrochemical cell?
A circuit made up of the anode, cathode, electrolyte, a power source and wires that connect two electrode
Why can’t an ionic solid be electrolysed?
Ions are fixed positions and can’t move whereas it can be electrolysed if it is molten because ions move freely and conduct electricity
In electrolysis in aqueous solutions, if H+ and metal ions present at cathode, what will be produced if the metal is more reactive than hydrogen and if less reactive?
If metal more reactive than hydrogen, hydrogen gas produced. If metal less reactive than hydrogen, solid layer of pure metal produced instead
In electrolysis in aqueous solutions, if OH- ions and halide ions present at anode, what will form? What will be formed if no halide ions are present?
If OH- and halide ions present, molecules of halogen will be formed. If no halide ions present, then oxygen will be formed.
What is the test for oxygen?
Collect gas in test tube and put glowing splint in it. If splint relights, oxygen present
When you electrolyse copper sulfate solution with inert electrodes, what is produced at anode and cathode? Half equations for both electrodes?
Copper less reactive than hydrogen so copper metal produced at cathode
Cu (2+) + 2e- –> Cu
No halide ions present so oxygen and water produced at anode
4OH (-) –> O2 + 2H2O + 4e-
What will happen if you set up an electrochemical cell but you using non-inert copper electrodes in a solution of copper sulfate instead of inert electrodes? Why
Mass of anode will decrease and mass of cathode will increase because copper transferred from anode to cathode
What affect will increasing the current have on rate of electrolysis?
Increase in rate so bigger difference between mass of two electrodes after same amount of time
