Question Video: Describing the Oxide of Aluminum | Nagwa Question Video: Describing the Oxide of Aluminum | Nagwa

Question Video: Describing the Oxide of Aluminum Chemistry • Second Year of Secondary School

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Al₂O₃ is an oxide that can react with acids as well as bases, as shown in the following equations: Al₂O₃ + 3 H₂SO₄ ⟶ Al₂(SO₄)₃ + 3 H₂O, Al₂O₃ + 2 NaOH ⟶ 2 NaAlO₂ + H₂O. Which of the following describes that oxide? [A] It is an amphoteric metal oxide. [B] It is an amphoteric nonmetal oxide. [C] It is a neutral metal oxide. [D] It is a neutral nonmetal oxide. [E] It is a peroxide.

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Video Transcript

Al2O3 is an oxide that can react with acids as well as bases, as shown in the following equations. Al2O3 plus three H2SO4 reacts to give Al2(SO4)3 plus three H2O. Al2O3 plus two NaOH reacts to give two NaAlO2 plus H2O. Which of the following describes that oxide? (A) It is an amphoteric metal oxide. (B) It is an amphoteric nonmetal oxide. (C) It is a neutral metal oxide. (D) It is a neutral nonmetal oxide. Or (E) it is a peroxide.

Al2O3, or aluminum oxide, reacts with acids as well as bases, the question tells us. The first equation in the question shows aluminum oxide reacting with H2SO4, which is sulfuric acid. And the second equation shows aluminum oxide reacting with NaOH, which is sodium hydroxide. Sodium hydroxide is a base. The question also tells us that Al2O3 is an oxide. An oxide is a chemical compound that contains at least one oxygen atom chemically bonded to an atom of another element. In the case of aluminum oxide, oxygen is bonded to aluminum, which is a metal. So aluminum oxide is a metal oxide. We can immediately rule out answer options (B) and (D), which both mention nonmetal oxides. Answer options (A) and (C) both mention metal oxides. But in (A), the metal oxide is described as amphoteric and in (C) as neutral.

Let’s have a look at how oxides are classified to distinguish between the remaining answers. Oxides can be acidic, basic, amphoteric, or neutral. Nonmetal oxides are often considered to be acidic because they dissolve in water to produce acid solutions. For example, SO3 in water react to give the acid sulfuric acid. Metal oxides are often basic because these oxides dissolve in water to form bases. For example, the oxide of magnesium when dissolved in water forms basic magnesium hydroxide. We know that when an acid and a base react with each other, a salt and water are produced. So any acidic nonmetal oxide can react with a base to produce salt and water, and any basic metal oxide can react with an acid to produce salt and water.

What about amphoteric oxides? Amphoteric oxides are those oxides that can act both as an acid and as a base. The two equations given to us in the question are examples of how the amphoteric oxide aluminum oxide can react with the acid sulfuric acid or the base sodium hydroxide to form salts and water. These two compounds are salts of aluminum.

Neutral oxides are neither acidic or basic in nature and do not react with acids or bases. An example of a neutral oxide is carbon monoxide. We have seen that because the metal oxide aluminum oxide can react with an acid such as sulfuric acid, it acts as a base. And when aluminum oxide reacts with a base such as sodium hydroxide, it acts as an acid. Therefore, we know it is an amphoteric metal oxide. Because it reacts with acids and bases, it cannot be a neutral oxide.

We have not discussed answer option (E). A peroxide is a compound which contains two oxygen atoms bonded to each other with a single covalent bond, for example, hydrogen peroxide, H2O2. The oxygen atoms in aluminum oxide, Al2O3, are each bonded to the aluminum atom. So this compound is not a peroxide. Finally, which of the following describes aluminum oxide? The answer is (A). It is an amphoteric metal oxide.

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