Electrolysis Flashcards
What happens during electrolysis
An … current is passed through an e… (a m… or dissolved i… compound) where the … move towards the e… reacting with them and the compound d….
An electric current is passed through an electrolyte (a molten or dissolved ionic compound) where the ions move towards the electrodes reacting with them and the compound decomposes
Cations have what charge
Positive
What electrode do the positive ions go to
The cathode
Anions have what charge
Negative
What happens when ions gain or lose electrons in electrolysis
They form the uncharged element and are discharged from the electrolyte
Why can’t and ionic solid be electrolysed
Because the ions are in a fixed position and can’t move
What things can be electrolysed
-Molten ionic compounds
-molten ionic liquids
What happens at the cathode
Positive metal ions are reduced
What happens at the anode
Negative non-metal ions are oxidised
Half equation at the cathode
……….2+. -
Eg Pb +2e. —> Pb
Half equation at the anode
2Br- —> Br2 + 2e-
What can metals be extracted from using electrolysis
Their ores
How can aluminium be extracted from them ores
- Aluminium is e… from the ore bauxite by e…. Bauxite contains Al2O3
- Aluminium oxide has a very … melting temp so it’s mixed with … to lower the … point
- The m… mixture contains free ions - so it conducts …
- The positive Al3+ ions go to the … where they gain … electrons and turn into … atoms, which then …
- The … O2- ions are attracted to the … where they … 2 electrons to form … molecules
- Aluminium is extracted from the ore bauxite by electrolysis. Bauxite contains Al2O3
- Aluminium oxide has a very high melting temp so it’s mixed with cryolite to lower the melting point
- The molten mixture contains free ions - so it conducts electricity
- The positive Al3+ ions go to the cathode where they gain 3 electrons and turn into Al atoms, which then sink
- The negative O2- ions are attracted to the anode where they lose 2 electrons to form oxygen molecules
What can be added to a reaction to lower the melting point
Cryolite
Half equation of extracting Al from its ore at the cathode
Al3+ + 3e- —> Al
Reduction
What charge ions do metals form
Positive
Half equation of extracting Al for its ore at the anode
2O2- —> O2 + 4e-
Oxidation
What reaction happens at the cathode
Reduction
What reaction happens at the anode
Oxidation
What is reduction
What is oxidation
-gain of electrons
-loss of electrons
O xidation
I s
L oss
R eduction
I s
G ain
What charge ions do non-metals form
Negative ions
Overall equation of extracting Al from its ore
2Al2O3 —> 4… + …O2
2Al2O3 —> 4Al + 3O2
What ions are present in aqueous solutions
-ions from the i… compound
-h… ions (H+)
-h… ions (OH-)
-ions from the ionic compound
-hydrogen ions (H+)
-hydroxide ions (OH-)
What happens if H+ ions and metal ions are present at the cathode
-if the … is … reactive than hydrogen then … gas will be produced
-if the metal is … reactive than … a solid layer of … metal is produced
-if the metal is more reactive than hydrogen then hydrogen gas will be produced
-if the metal is less reactive than hydrogen a soldi layer of pure metal is produced
What happens at the anode when OH- and halide ions are present
Molecules of the halide eg Cl2, Br2 will be formed
What happens at the anode if no halide ions are present
The …- ions are discharged forming …
The OH- ions are discharged forming oxygen and water
Half equation at the cathode if the metal is less reactive than hydrogen
Eg Cu2+ + …- —> Cu
Eg Cu2+ + 2e- —> Cu
Half equation at the cathode if the metal is more reactive than hydrogen
…H+ + 2e- —> …
2H+ + 2e- —> H2
Half equation at anode if no halide ions present
…OH- —> … + 2H2O + 4…-
4OH- —> O2 + 2H2O + 4e-
Half equation at the anode if halide ions are present
Eg Cl- —> Cl2 + …-
Eg Cl- —> Cl2 + 2e-
Electrolysis
The process of breaking down a substance using electricity
