5.4.1 - electrolysis of molten compounds Flashcards
what is electrolysis
the breaking down of a compound using electricity
during electrolysis what is the substance to be broken down connected to
a circuit with a cell or battery
what are the two electrodes that connect the substance into the circuit called
- anode
- cathode
what is the positive electrode called
anode
what is the negative electrode called
cathode
what must electrodes be made from
a solid that conducts electricity but is inert
usually graphite (cheap) or platinum (expensive)
what is the substance to be broken down called
the electrolyte
what does the electrolyte need
needs to conduct electricity
what are the only compounds that conduct electricity
ionic compounds that are molten or dissolved so the ions are free to move
solid ionic compounds wont work because the ions can’t move, and covalent compounds wont work because the molecules aren’t even charged
what are the names of the ions in the compound (due to which electrode they are attracted to)
- cations
- anions
what are positive ions called 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 is the general formula for electrolysis of molten ionic compounds
compound -> elements
what happens at the anode during molten electrolysis:
(eg. with Cl and Mg)
- NON-METAL IONS LOSE ELECTRONS TO FORM MOLECULES
- the Cl- ions are attracted to the anode as they lose electrons to form neutral Cl atoms
- as each Cl- has a 1- charge, they lose one electron each to become neutral
- non-metals are made of diatomic molecules, so the Cl atoms pair up to form Cl2 molecules
2Cl- -> Cl2 + 2e-
- 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
what happens at the cathode during molten electrolysis:
(eg. with Cl and Mg)
- METAL IONS GAIN ELECTRONS TO FORM ATOMS
- 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 2 electrons each to become neutral
- metals aren’t made of molecules, so the atoms don’t pair up
- Mg2+ + 2e- -> Mg
- 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
