Question Video: Detecting the Electrode at Which Lead or Bromide Is Oxidized or Reduced in the Electrolysis of Molten Lead Bromide Chemistry

In the electrolysis of molten lead bromide, shown in the picture, which electrode is on the right? [A] The cathode, as it is oxidizing the bromine [B] The cathode, as it is reducing the bromide ions [C] The anode, as it is reducing the bromide ions [D] The anode, as it is oxidizing the bromide ions [E] The anode, as it is oxidizing the bromine

03:57

Video Transcript

In the electrolysis of molten lead bromide, shown in the picture, which electrode is on the right? (A) The cathode, as it is oxidizing the bromine. (B) The cathode, as it is reducing the bromide ions. (C) The anode, as it is reducing the bromide ions. (D) The anode, as it is oxidizing the bromide ions. Or (E) the anode, as it is oxidizing the bromine.

This picture depicts the electrolysis of molten lead bromide with a brown gas wafting up from one of the electrodes. This brown gas is bromine gas. This question is asking us to describe how bromine gas forms and at which electrode. Each choice has three parts, meaning there’s three pieces of information we need to gather in order to answer the question. Is bromine gas produced at the anode or the cathode? When bromine gas is produced, does it involve an oxidation or a reduction? And does that oxidation or reduction happen to bromide ions or bromine atoms?

Let’s start with the third piece of information. Does this process involve bromide ions or bromine atoms? Molten lead bromide is made up of free-floating lead ions and bromide ions. Electrolysis requires an electrolyte. An electrolyte is a substance made up of ions or able to release ions that can conduct electricity. When the circuit is turned on, the bromide ions are drawn to one of the electrodes to begin the formation of bromine gas. Since the reactants in this process are bromide ions and not bromine atoms, we can eliminate choice (A) and choice (E) from consideration.

Next, let’s consider the name of the electrode. The negatively charged bromide ions are known as anions. This is in contrast to the positively charged lead cations. Which electrode, the anode or the cathode, are anions drawn to? Well, we can remember that their names correspond with one another. Anions are drawn to the anode, and cations are drawn to the cathode. In this example, bromide anions are drawn to the anode, so we can eliminate choice (B) from consideration as well.

The last question to consider is whether these bromide ions are being oxidized or reduced at the anode. Let’s take a look at what happens to the bromide ions at the anode in order to answer this question. First, each bromide ion donates an electron to the anode. Then, the ions that have donated their extra electrons can pair up to form a bromine gas molecule. The half reaction for this process is 2Br- ions produce Br2 and two electrons. With this process in mind, are the bromide ions being oxidized or reduced?

In this situation, since the bromide ions are giving up or losing their electrons, it’s an oxidation. On the other hand, a reduction is when an atom or ion gains electrons. For example, at the cathode in this experiment, the lead ions will gain electrons or be reduced to form elemental lead. Since the bromide ions are losing electrons or being oxidized, we can identify (D) as the correct answer. The electrolysis of molten lead bromide produces the brown bromine gas as a product. The bromide ions are attracted to the anode, where they donate electrons to form bromine gas. Since the bromide ions lose electrons, we also call this process an oxidation.

So in the electrolysis of molten lead bromide, shown in the picture, which electrode is on the right? That’s choice (D), the anode, as it is oxidizing the bromide ions.

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.