Problem 31 - Chemistry An Atoms First Approach

Question

\(\mathrm{Al}_{2} \mathrm{O}_{3}\) is amphoteric. What does this mean?

Step-by-Step Solution

Answer

\(\mathrm{Al}_{2} \mathrm{O}_{3}\) is amphoteric, which means it can react both as an acid and as a base, depending on the environment. In an acidic environment, it exhibits basic behavior by accepting protons from an acid, whereas in a basic environment, it exhibits acidic behavior by donating protons to a base. This dual behavior allows it to react with different species in various environments, making it versatile in chemical processes and practical applications.

Step 1: Definition of Amphoteric

An amphoteric substance is a substance that can react both as an acid and as a base, depending on the environment it is in. This means that an amphoteric compound will exhibit dual behavior and can donate or accept protons (H+ ions) in chemical reactions, depending on the other species present in the solution.

Step 2: Amphoteric Behavior of \(\mathrm{Al}_{2} \mathrm{O}_{3}\) in Acidic Solution

In an acidic environment, \(\mathrm{Al}_{2} \mathrm{O}_{3}\) will exhibit basic behavior by reacting with an acid. The reaction proceeds as: \[ \mathrm{Al}_{2} \mathrm{O}_{3} + 6\mathrm{HCl} \rightarrow 2\mathrm{AlCl}_{3} + 3\mathrm{H}_{2}\mathrm{O} \] In this reaction, \(\mathrm{Al}_{2} \mathrm{O}_{3}\) accepts protons (H+ ions) from the hydrochloric acid (HCl) to form aluminum chloride (AlCl\(_3\)) and water (H\(_2\)O).

Step 3: Amphoteric Behavior of \(\mathrm{Al}_{2} \mathrm{O}_{3}\) in Basic Solution

In a basic environment, \(\mathrm{Al}_{2} \mathrm{O}_{3}\) will exhibit acidic behavior by reacting with a base. The reaction proceeds as: \[ \mathrm{Al}_{2} \mathrm{O}_{3} + 2\mathrm{NaOH} + 3\mathrm{H}_{2} \mathrm{O} \rightarrow 2\mathrm{Na}[Al(OH)_4] \] In this reaction, \(\mathrm{Al}_{2} \mathrm{O}_{3}\) donates protons (H+ ions) to the sodium hydroxide (NaOH) to form a complex sodium aluminate ([Al(OH)\(_4\)]ˉ) and water (H\(_2\)O). By understanding the properties and behavior of amphoteric compounds like \(\mathrm{Al}_{2} \mathrm{O}_{3}\), we can better predict their reactions in various environments and use this knowledge in practical applications, such as the synthesis of new materials and the manipulation of chemical processes.