Electrolysis of Molten Compounds
Electrolysis of Molten Compounds
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e.g. Electrolysis on MOLTEN Sodium Chloride will always form SODIUM and CHLORINE whereas AQUEOUS Sodium Chloride does not (see later notes).
Let’s look at the process for the example of MOLTEN SODIUM CHLORIDE electrolyte:
The IONS involve in this example are Na+ and Cl-. This means that the electrolyte has these ions floating around in it.
When the circuit is turned on, and electricity flows, the Na+ ions get attracted to the CATHODE and the Cl- ions get attracted to the ANODE.
When they reach the anodes, both sets of ions TRANSFER ELECTRONS and turn into ATOMS of ELEMENTS.
Na+ IONS turn into Na ATOMS, while Cl- ions turn into Cl ATOMS. To represent these processes, you can write their HALF EQUATIONS.
To write ELECTROLYSIS HALF EQUATIONS, you can follow these steps:
Write the ION of the element on the LEFT, and the ATOM of the element on the RIGHT.
Check if any of the elements are DIATOMIC (exist as two atoms). Here is a list of ALL the DIATOMIC elements you need to know.
Chlorine is part of the list so it needs to be changed to Cl2.
BALANCE the equation to make sure you have the same numbers on the left and right.
Add ELECTRONS to make the charges in the equation balanced.
In this example, each chlorine atom LOSES an electron so there are TWO electrons on the right. This gives the final ANODE half equation as:
We can do the same for the CATHODE to find the half equation for Sodium.
The set up for Aluminium extraction is slightly different to the normal classroom set up:
There is usually more than one anode submerged in the electrolyte, and the cathode lines the INSIDE of the container. Both electrodes are made of GRAPHITE.
The ions present in the liquid include POSITIVE ALUMINIUM IONS (Al3+) and NEGATIVE OXYGEN IONS (O2-).
When current flows through the set up, the ALUMINIUM ions are attracted to the CATHODE, and the OXYGEN ions are attracted to the ANODE.
To find the HALF EQUATION for this process, you can follow the normal steps:
The final products in this electrolysis are ALUMINIUM metal and OXYGEN gas.
The Aluminium is produced as a MOLTEN LIQUID which flows to the bottom of the container due to the HIGH TEMPERATURE.
The Oxygen is produced as BUBBLES which float to the top of the liquid.
During this process the GRAPHITE ANODES need to be REPLACED REGULARLY. This is because they WEAR AWAY as the OXYGEN formed at the ANODES react with the CARBON in the graphite to form CARBON DIOXIDE.
e.g. Electrolysis on MOLTEN Sodium Chloride will always form SODIUM and CHLORINE whereas AQUEOUS Sodium Chloride does not (see later notes).
Let’s look at the process for the example of MOLTEN SODIUM CHLORIDE electrolyte:
The IONS involve in this example are Na+ and Cl-. This means that the electrolyte has these ions floating around in it.
When the circuit is turned on, and electricity flows, the Na+ ions get attracted to the CATHODE and the Cl- ions get attracted to the ANODE.
When they reach the anodes, both sets of ions TRANSFER ELECTRONS and turn into ATOMS of ELEMENTS.
Na+ IONS turn into Na ATOMS, while Cl- ions turn into Cl ATOMS. To represent these processes, you can write their HALF EQUATIONS.
To write ELECTROLYSIS HALF EQUATIONS, you can follow these steps:
Write the ION of the element on the LEFT, and the ATOM of the element on the RIGHT.
Check if any of the elements are DIATOMIC (exist as two atoms). Here is a list of ALL the DIATOMIC elements you need to know.
Chlorine is part of the list so it needs to be changed to Cl2.
BALANCE the equation to make sure you have the same numbers on the left and right.
Add ELECTRONS to make the charges in the equation balanced.
In this example, each chlorine atom LOSES an electron so there are TWO electrons on the right. This gives the final ANODE half equation as:
We can do the same for the CATHODE to find the half equation for Sodium.
The set up for Aluminium extraction is slightly different to the normal classroom set up:
There is usually more than one anode submerged in the electrolyte, and the cathode lines the INSIDE of the container. Both electrodes are made of GRAPHITE.
The ions present in the liquid include POSITIVE ALUMINIUM IONS (Al3+) and NEGATIVE OXYGEN IONS (O2-).
When current flows through the set up, the ALUMINIUM ions are attracted to the CATHODE, and the OXYGEN ions are attracted to the ANODE.
To find the HALF EQUATION for this process, you can follow the normal steps:
The final products in this electrolysis are ALUMINIUM metal and OXYGEN gas.
The Aluminium is produced as a MOLTEN LIQUID which flows to the bottom of the container due to the HIGH TEMPERATURE.
The Oxygen is produced as BUBBLES which float to the top of the liquid.
During this process the GRAPHITE ANODES need to be REPLACED REGULARLY. This is because they WEAR AWAY as the OXYGEN formed at the ANODES react with the CARBON in the graphite to form CARBON DIOXIDE.
