Video: Identifying the Best Description of the Conversion of Copper Oxide to Copper in a Set of Descriptions

Which of the following best describes the conversion of copper oxide to copper? [A] Fusion [B] Precipitation [C] Nuclear transformation [D] Combustion [E] Reduction.


Video Transcript

Which of the following best describes the conversion of copper oxide to copper? A) Fusion, B) Precipitation, C) Nuclear transformation, D) Combustion, or E) Reduction.

The question references copper oxide, which could either be copper two oxide or copper one oxide. So we could be dealing with CuO, copper two oxide, otherwise known as cupric oxide. Or we could be dealing with Cu₂O, otherwise known as cuprous oxide or copper one oxide. As we’ll come to see, it doesn’t make a difference for this question. So I’m going to write CuO throughout. But bear in mind, it could equally be Cu₂O. Either way, we’re looking at the conversion of a copper oxide to metallic copper. The set-up for this conversion might look like the following, where we have a Bunsen burner heating a sample of copper oxide powder inside a tube. Hydrogen gas will be introduced into the powder where it would react, forming water and copper metal.

The hydrogen might come from a cylinder or, for a simple laptop demonstration, we might use a mixture of zinc and hydrochloric acid to produce the hydrogen gas. And here, we have the balanced equation for the reaction of copper two oxide with hydrogen forming copper and water. Now that we’ve had a recap of the whole process, let’s have a look at the descriptions to see which one best applies. Remember, we’re looking for the best description. So more than one may apply.

The word fusion isn’t used much with chemical reactions. It’s more common to see it in terms of nuclear reactions. For instance, the conversion of four hydrogen nuclei to form a helium nucleus, as goes on in the sun. In fact, the sun consumes about 600 million tons of hydrogen every second. In the conversion of copper oxide to copper, all the components preserve their elemental identity. We don’t see elements fusing together, so it’s not a fusion reaction.

A precipitation reaction is where we produce a solid from a solution. A good example of a precipitation reaction is the reaction of lead nitrate with potassium iodide, which produces the brilliant yellow precipitate lead iodide. We’re not dealing with anything in solution. Only the conversion of solid copper oxide, which is insoluble in water, to metallic copper, which is also insoluble.

A nuclear transformation process is one where we see a change in the composition of one or more nuclei. For example, we see this kind of transformation in nuclear decay processes. For instance, thorium 234 transforming into protactinium 234 with the release of a beta particle, among other things. As with fusion, nuclear transformation is not a good description of the conversion of copper oxide to copper because no component changes its elemental identity. All the nuclei retain their original composition and just rearrange themselves.

Meanwhile, combustion is the reaction with oxygen. For instance, in the complete combustion of methane, one molecule of methane reacts with two molecules of oxygen, forming a molecule of carbon dioxide and two molecules of water. There’s no molecular oxygen present in our reaction equation. So it’s not the combustion.

This leaves us with one option, reduction. In a reduction reaction, we’ll see a reduction in the oxidation state of one or more components. This usually means that they gain electrons. The oxidation state of copper in copper two oxide is plus two. This counterbalances the default oxidation state for oxygen in oxide of negative two. Hydrogen, in its elemental form, will have an oxidation state of zero, as will copper, our product. Hydrogen in water will have an oxidation state of positive one. And oxygen will have an oxidation state of negative two.

In this reaction, the stars of our show are copper oxide and copper. So let’s have a look at the oxidation state of copper and how it changes. The oxidation state of copper goes from positive two to zero. So we see a reduction in its oxidation state. So this reaction is most certainly a reduction reaction. However, the sharp-eyed among you might have noticed we’re also dealing with an oxidation of hydrogen, going from zero to positive one. Whenever a reduction occurs, an oxidation must also occur. So we have the term redox reaction. However, it’s perfectly okay to focus on only one component and describe its individual reaction. In which case, we can describe the conversion of copper oxide to copper as a reduction reaction.

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