Electrolysis and Extracting Metals Flashcards
What is oxidisation?
What is reduction?
What is the pneumonic to rememer?
Process of losing electrons in a reaction
Process of gaining electrons in reaction
(OIL RIG)
Why do molten compounds conduct electricity?
How do aqueous solutions conduct electricity?
- Ions are free to move (breaks ionic lattice)
- allows flow of charge to move = electrical current
- when substance dissolves in water, ionic bonds are broken
- splits compound into its ions which are free to move
Describe the (typical) electrodes used in electrolysis What process happens at each electrode?
Usually made of carbon (graphite) as it is good electrical conductor
Anodes are positive electrodes as they attract anions- OXIDATION
Cathodes are negative as they attract cations- REDUCTION
What is an electrolyte?
Substance that has electricity passed through it
What are the half equations for electrolysis of molten compounds?
At cathode:
Positive cation reduced (gains electrons) to form element
At anode:
Negative anion oxidised (loses electrons) to form element
What are the rules for the electrolysis of aqueous solutions?
At cathode:
If metal MORE reactive than hydrogen, HYDROGEN is produced.
If metal is Cu, Ag, Au or Platinum, metal is produced.
At anode:
If non-metal is halide, halogen is produced.
Else 4OH- minus 4e- ——-> 2H2O and O2.
(The metal/hydrogen and non-metal/hydroxide that hasn’t reacted will react together eg. Sodium Hydroxide)
What are the uses of:
Chlorine? Hydrogen? Sodium hydroxide (brine)?
What apparatus is used in industry for electrolysis of brine?
Killing bacteria in water, bleach | Making margarine | Making soap and paper
Diaphragm cell (diaphragm in middle to separate products as toxic)
What is the standard method for electrolysis calculations?
1) balanced half equations
2) Q = IT
3) moles of electrons = Q/F
4) molar ratio
5) moles to mass/volume
What is the definition of electrolysis?
The use of electricity to separate compounds into elements
How is aluminium extracted from its main ore?
Bauxite (main ore) is treated to produce pure aluminium oxide, which has high melting point so would be too expensive.
Al2O3 is dissolved in molten cryolite to reduce melting point.
learn diagram
Aluminium produced at cathode, oxygen at anode
What machine is used for extraction of iron?
Blast furnace
What are the inputs into extraction of iron?
Iron ore (hematite) , limestone and coke (carbon)
Write the 4 equations that occur in extraction of iron
C + O2 —> CO2
CO2 + C —> 2CO
Fe2O3 + 3CO —> 2Fe + 3CO2
SiO2 + CaCO3 –> CaSiO3 + CO2
Why do covalent compounds not conduct electricity?
They have no free electrons and no ions
No flow of charge
What does one Faraday represent and what is its value?
Represents one mole of electrons
96 500 C
