Video Transcript
Sodium metal could be prepared from its ore by the electrolysis of molten sodium chloride. Which of the following best describes this process? (A) Chloride ions are oxidized at the cathode, and sodium ions are reduced at the anode. (B) Chloride ions are reduced at the anode, and sodium ions are oxidized at the cathode. (C) Chloride ions are oxidized at the anode, and sodium ions are reduced at the cathode. Or (D) chloride ions are reduced at the cathode, and sodium ions are oxidized at the anode.
Metals like sodium are often extracted from naturally occurring materials called ore. The ores are often mined from the Earth. It is then processed, and then valuable material is made from this processing. And sodium is an example of a metal that can be prepared in this way. And sodium is extracted from its ore using the technique of electrolysis. Electrolysis is a chemical process where electricity is passed through an electrolyte, causing it to decompose into its constituent elements.
In the process of electrolysis, a current is passed through a solution containing ions using an anode, which is the positive electrode in an electrolytic cell, and a cathode, which is the negative electrode in an electrolytic cell. At the anode of an electrolytic cell, negatively charged ions such as chloride are attracted to the positive electrode, and they tend to lose electrons here. In this example, when the chloride ion loses an electron, we say that it is oxidized. And at the cathode of an electrolytic cell, positively charged ions such as sodium are attracted to the negative charge of the cathode. Here they tend to accept electrons from the cathode. In this case, we say that sodium is reduced.
In this process of gaining and losing electrons, the properties of substances are altered. In order to more clearly analyze the case of sodium chloride, let’s simplify by using half reaction equations that describe what is happening at the two electrodes. Like we’ve already said, at the cathode, positively charged sodium ions gain an electron to form sodium metal. And this process is called reduction. And at the positively charged anode, chloride ions lose electrons to form chlorine gas. And this loss of electrons is known as oxidation.
With this information at hand, we should be able to revisit the question. Sodium metal could be prepared from its ore by the electrolysis of molten sodium chloride. Which of the following best describes this process? Answer choice (A) says that chloride ions are oxidized at the cathode and sodium ions are reduced at the anode. And we know that this cannot be correct because oxidation does not take place at the cathode and reduction does not take place at the anode. Answer choice (B) says that chloride ions are reduced at the anode and sodium ions are oxidized at the cathode. But we know that this cannot be true because chloride ions are not reduced and sodium ions are not oxidized.
Using the same logic, we can also eliminate answer choice (D) because chloride ions are not reduced and sodium is not oxidized. And that leaves us with answer choice (C) where chloride ions are oxidized at the anode and sodium ions are reduced at the cathode.
