Video: Reaction of Sulfuric Acid with Cupric Oxide

Ores containing cupric oxide (CuO) are commonly reacted with sulfuric acid to produce a copper-containing material that is more easily processed. This process is known as sulfuric acid leaching. a) Write a balanced chemical equation for the reaction of cupric oxide with sulfuric acid. b) What is the name of the copper-containing compound produced when cupric oxide reacts with sulfuric acid? c) What is the main reason for sulfuric acid leaching of cupric oxide ores? [A] The product of the reaction is more soluble than cupric oxide. [B] The product of the reaction has a lower melting point than cupric oxide. [C] The product of the reaction is less toxic than cupric oxide. [D] The product of the reaction is less stable than cupric oxide so it can be electrolyzed more easily. [E] The product of the reaction forms smaller crystals than cupric oxide so it can be ground up more easily. d) To obtain metallic copper, the product of sulfuric acid leaching is reacted with another elemental metal. By considering their relative costs and reactivities, determine which of the following metals is most suitable for use in this reaction. [A] Lead [B] Silver [C] Sodium [D] Aluminium [E] Iron

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Video Transcript

Ores containing cupric oxide, CuO, are commonly reacted with sulfuric acid to produce a copper containing material that is more easily processed. This process is known as sulfuric acid leaching. Write a balanced chemical equation for the reaction of cupric oxide with sulfuric acid.

Cupric oxide is another name for copper(II) oxide. Cupric is used to indicate a compound where copper is in the plus two oxidation state. For reference, Cu⁺ is indicated by the word cuprous. Sulfuric acid, meanwhile, is a solution of H₂SO₄ in water. So what we’re looking at here is the reaction of copper(II) oxide with sulfuric acid. On the road to our balanced chemical equation, writing the formula for cupric oxide is the first step. The next reactor is sulfuric acid. And the question we need to ask ourselves is, What are the products?

Cupric oxide is a metal oxide, and sulfuric acid is an acid. The expected outcome from such a reaction is a metal salt plus water. When sulfuric acid is used, we expect the salt to be a sulfate. This is because when sulfuric acid reacts with a metal oxide, it will give up two H+ ions, leaving behind the SO four two minus anion. You can see how the sulfuric acid and the sulfate have these atoms in common. Therefore, the salt we expect is copper sulfate. We know the formula for copper(II) sulfate is CuSO₄ because the two positive charge of the copper ion counterbalances perfectly that two minus charge of the sulfate anion.

Now, all we need to do is check that it’s balanced. There’s one equivalent of copper on the reactant side and the product side, two equivalents of hydrogen on both sides, one equivalent of sulfur on both sides, and five equivalents of oxygen on both sides. The equation is, therefore, balanced. So for the reaction of cupric oxide with sulfuric acid, the balanced chemical equation is CuO plus H₂SO₄ react to form CuSO₄ plus H₂O.

What is the name of the copper containing compound produced when cupric oxide reacts with sulfuric acid?

For this question, we can simply go back to the word equation. We know that sulfuric acids react to produce sulfates, and the cupric refers to copper(II). So our products are copper(II) sulfate and water. So the name given to the copper-containing compound produced when cupric oxide reacts with sulfuric acid is copper(II) sulfate. Alternatively, you could substitute copper(II) for cupric and cupric sulfate. Or you could use its common name, copper sulfate, where it is assumed that copper is in its most common oxidation state, plus two.

What is the main reason for sulfuric acid leaching of cupric oxide ores? A) The product of the reaction is more soluble than cupric oxide. B) The product of the reaction has a lower melting point than cupric oxide. C) The product of the reaction is less toxic than cupric oxide. D) The product of the reaction is less stable than cupric oxide so it can be electrolyzed more easily. Or E) The product of the reaction forms smaller crystals than cupric oxide so it can be ground up more easily.

Here we’ve been given five possible reasons for sulfuric acid leaching. Remember that the main reason for doing all this is because we want to obtain pure copper at the end. So sulfuric acid leaching takes us partway from copper oxide to a solution of copper sulfate. Copper oxide is insoluble solid, while a solution of copper sulfate is liquid. This makes it easier to convert the substance to pure copper. The solution is mixed with other chemicals that allow it to be reduced. Grinding up the pure ore, which would possibly have other contaminants in it as well, would be much less effective. The main reason for sulfuric acid leaching is to produce this solution of copper sulfate. This highlights option A. The product of the reaction is more soluble than cupric oxide as the best answer. But I’m going to look through the other answers just in case.

The second statement says that the product of the reaction has a lower melting point than cupric oxide. After sulfuric acid leaching, the product is not melted. Copper is not reactive enough to react with water and, therefore, can undergo solution phase reactions and does not need to be purified by electrolysis. Therefore, this is not the reason for sulfuric acid leaching. The third statement is that the product of the reaction is less toxic than cupric oxide. The truth of the matter is that both cupric oxide and copper sulfate are toxic. The copper sulfate produced is quickly converted into other things. So whether or not it’s less toxic is not really an issue. Therefore, this, too, is not a correct answer.

The fourth option says that the product of the reaction is less stable than cupric oxide so it could be electrolyzed more easily. The stability of a salt is not as important as its solubility when it comes to solution electrolysis. So even if the solution would be electrolyzed, the stability of the salt would not be an issue.

Now, we can move on to the last statement. The last possible reason is that the product of the reaction forms smaller crystals than cupric oxide so it could be ground up more easily. The product in question, copper sulfate solution, is kept as a solution. This way, it can be more easily introduced to the other processing steps. Therefore, it does not need to be ground up. So whether it’s easier or harder does not really matter. Therefore, this is an incorrect answer. So the correct answer for the main reason for sulfuric acid leaching of cupric oxide ores is that the product of the reaction is more soluble than cupric oxide.

To obtain metallic copper, the product of sulfuric acid leaching is reacted with another elemental metal. By considering their relative costs and reactivities, determine which of the following metals is most suitable for use in this reaction. A) Lead. B) Silver. C) Sodium. D) Aluminium. Or E) Iron.

Just for reference, recall that the product of sulfuric acid leaching is a solution of copper sulfate. To start off with this question, I’m going to look at the reactivities of the metals involved. What we want to achieve here is the reduction of copper(II) plus ions. The metal is supposed to react with the copper(II) ions in solution and turn them into copper metal. In the process, these metal atoms are going to form metal ions of their own. For this to occur, the metal must be more reactive than copper. Lead is higher up the reactivity series than copper. Therefore, it’s capable of displacing copper ions from solution. Silver is less reactive than copper. Therefore, it is incapable of participating in this reaction. So silver is definitely not a correct answer.

Sodium looks promising to start with because it is more reactive than copper. Unfortunately, sodium reacts with water quite violently. A solution of copper sulfate is mostly water. So sodium would react with the water before it reacts with a copper sulfate and would be highly ineffective and dangerous to use. Therefore, it is not a correct answer. Meanwhile, aluminium above copper in the reactivity series is not so far above that it react so violently with water. Therefore, it’s still a candidate. Iron, too, is more reactive than copper, so will be effective in displacing copper ions from solution.

The second factor in the question is cost. Ideally, we’re looking for the metal that is the least expensive. We’ve already eliminated silver. But we could be doubly sure about eliminating it because it is extremely expensive. Lead and aluminium are relatively cheap. Aluminium is produced by electrolysis, which raises the cost a little. However, it’s produced on very large quantities, allowing for economies of scale. Meanwhile, sodium, also produced by electrolysis, is a bit more of a niche product. So it’s less cheap than aluminium. Iron, on the other hand, is the most popular metal on the planet. Like lead, it’s produced in a blast furnace, but on much, much bigger scales.

This makes iron the best candidate based on relative cost and reactivity. If you’re interested, here are the current prices in bulk for each of the metals. As you can see, iron is the cheapest, with sodium at about twice the price and silver at about 370 times the price. The costs of lead and aluminium are on the same order of magnitude as the cost of iron. So we can be confident that, based on relative cost and reactivity, iron is the best candidate out of these five metals for use in this reaction.

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