Question Video: Explaining Why Aluminum ore Must be Molten During Electrolysis | Nagwa Question Video: Explaining Why Aluminum ore Must be Molten During Electrolysis | Nagwa

Question Video: Explaining Why Aluminum ore Must be Molten During Electrolysis Chemistry • Third Year of Secondary School

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Why must the aluminum ore be melted before it is electrolyzed?

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Video Transcript

Why must the aluminum ore be melted before it is electrolyzed?

Aluminum metal is a very important metal in the modern world. It’s used widely in items ranging from frying pans to drink cans to aircraft components. Since aluminum is a very reactive metal, it cannot be extracted by reduction of the ore with carbon. Simply heating aluminum oxide with carbon to very high temperatures will not produce any aluminum metal. No reaction will occur in this case as carbon is simply not a powerful enough reducing agent to reduce the aluminum oxide.

Instead, to extract aluminum from aluminum ore, we need to use a process called electrolysis. Electrolysis is a chemical process where electricity is passed through an electrolyte, causing it to decompose into its constituent elements. During the extraction of aluminum, a rock called bauxite is mined from the ground. Bauxite is a form of aluminum ore, and at this stage it’s very impure. The bauxite must be refined chemically, and aluminum oxide is extracted. Aluminum oxide is also known as alumina. It has the chemical formula Al2O3, and at this stage it’s very pure. Aluminum oxide is then placed into an electrolysis cell where aluminum will be extracted.

The electrolysis cell consists of a carbon cathode and a carbon anode. The cathode is the negative electrode in this cell, and the anode is the positive electrode. When the cell is operating, it’s filled with a molten electrolyte. An electrolyte is an electrical conductor. It’s a substance that contains freely moving ions. As the electrolysis proceeds, molten aluminum is produced at the cathode or negative electrode and it flows from the bottom of the cell. Positively charged aluminum ions gain three electrons from the cathode to become aluminum atoms. This is a reduction reaction as the aluminum ions are gaining three electrons from the cathode here. The liquid aluminum atoms sink to the bottom of the cell as they are more dense than the surrounding molten electrolyte.

The molten electrolyte also contains oxide ions, which are negatively charged ions. The oxide ions arrive at the anode, or positive electrode, where they give up electrons and turn into oxygen gas. Since electrons are given away by the oxide ions at the anode, this is an oxidation reaction that’s happening here. Although oxygen gas bubbles are initially produced at the carbon anode, they will react with the anode at the temperature of the cell and produce carbon dioxide gas. The anode slowly burns away in this process. Since the anode and cathode occupy fixed positions in this electrolysis cell, we can see that the aluminum ions and the oxide ions must be free to move around for the process to work. The mobile ions allow charge to flow through the cell so that it conducts electricity.

So to answer the question “Why must the aluminum ore be melted before it’s electrolyzed?” it’s so that it contains mobile ions. This is to give the aluminum and oxide ions the ability to move. To give the aluminum and oxide ions the ability to move is the correct answer.

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