Electrolysis Flashcards
How does electrolysis work?
An electric current is passed through the electrolyte causing
ions to move to the electrodes.
Ions are discharged at the electrodes, producing elements.
Why is aqueous electrolysis generally cheaper than molten electrolysis?
In aqueous electrolysis the substance is just dissolved in water, no energy is required to melt it.
Why is cryolite used in the electrolysis of aluminium oxide?
Aluminium oxide has a very high melting point so it would be very expensive to melt.
Cryolite lowers the melting point of the aluminium oxide, therefore reducing the cost of the process.
Why is electrolysis not used to extract all metals?
Because electrolysis is very expensive (due to requiring lots of electricity).
In the electrolysis of molten lead bromine (PbBr2), what would be the half equation for the reaction at the negative electrode (cathode)?
Pb2+ + 2e- ➔ Pb
Why can’t ionic solids be electrolysed?
Ionic solids can’t be electrolysed as the ions are in fixed positions - they can’t move and carry charge
Why can molten ionic compounds be electrolysed?
The ions can move freely when the ionic compound is molten and thus they can conduct electricity.
In aqueous, what is the rule for determining which ion will be oxidised at the anod
OH-, unless there is a halide ion (such as Cl-, or Br-) present.
What happens to negative ions during electrolysis?
They move towards the anode (positive electrode).
They lose electrons.
This means they have been oxidised.
What is an electrode?
An electrode is a solid that conducts electricity and is submerged in the electrolyte.
In the electrolysis of aqueous sodium chloride, NaCl (aq), which ions will be reduced at the cathode (negative electrode)?
Hydrogen ions (H+)
In the electrolysis of aqueous solutions, what is the rule for determining which ion will be reduced (gain electrons) at the cathode (negative electrode)?
It will always be the H+ ion, unless it is the ion of the least reactive element
In the electrolysis of a solution, which two ions are present from the water molecules themselves?
H+ ions and OH- ions.
What happens to positive ions during electrolysis?
They are attracted to the cathode (negative electrode).
They gain electrons.
This means they have been reduced.
In the electrolysis of aqueous potassium bromide, KBr (aq), which 4 ions would be present in the electrolyte?
Potassium ions (K+)
Bromide ions (Br-)
Hydrogen ions (H+)
Hydroxide ions (OH-)
