Molten Electrolysis Flashcards
what is electrolysis?
electrolysis is the breaking down of a compound using electricity
what is the substance to be broken down connected to?
a cell or battery
what is the positive electrode called?
anode
what is the negative electrode called?
cathode
what must the electrodes be made of?
a solid that conducts electricity but is inert (unreactive) - usually, graphite (cheap) or platinum (expensive) are used
what is the electrolyte?
the substance to be broken down, it needs to conduct electricity
what are the compounds that conduct electricity?
- ionic compounds that are molten or dissolved so the ions are free to move
- solid ionic compounds won’t work because the ions can’t move, and covalent compounds won’t work because the molecules aren’t even charged
what are positive ions called and why?
cations - because they are attracted to the cathode
what are negative ions called and why?
anions - because they are attracted to the anode
what does electrolysis of a molten ionic compound produce?
its elements
what happens at the anode in electrolysis?
non-metals ions lose electrons to form molecules
what happens at the cathode in electrolysis?
metal ions gain electrons to form atoms
in the electrolysis of molten magnesium chloride, what happens at the anode?
- the Cl- ions are attracted to the anode and they lose electrons to form neutral Cl atoms
- as each Cl- ion has a 1- charge, they lose one electron each to become neutral
- non-metals are made up of diatomic molecules, so the Cl atoms pair up to form Cl2 molecules
- the Cl- ions have been oxidised because they have lost electrons
- as Cl2 is a pale green gas, some bubbles of pale green gas would likely be seen at the anode
in the electrolysis of molten magnesium chloride, what happens at the cathode?
- the Mg2+ ions are attracted to the cathode and they gain electrons to form neutral Mg atoms
- as each Mg2+ ion has a 2+ charge, they gain two electrons each to become neutral
- metals aren’t made of molecules, so the atoms don’t pair up
- we write this as a half-equation, showing the Mg2+ ions gaining electrons and becoming atoms
- the Mg2+ ions have been reduced because they have gained electrons
- as Mg is a grey solid, some grey solid would form on the surface of the cathode
what happens at the anode in the electrolysis of molten aluminium oxide?
- O2- ions are oxidised because they lost electrons
- bubbles of colourless gas would be observed at the anode
what happens at the cathode in the electrolysis of molten aluminium oxide?
- Al3+ ions are reduced because they gain electrons
- a shiny grey solid would be observed at the cathode
