Question

Some metal oxides react with acid as well as base to produce salt and water, these are known as amphoteric oxides. The examples of amphoteric oxides are:

• A. \(Al_2O_3\) and \(SiO\)
• B. \(Al_2O_3\) and \(ZnO\)
• C. \(CuO\) and \(ZnO\)
• D. \(CuO\) and \(SiO\)

Hint:

The two most common amphoteric oxides in secondary school chemistry are:
- Aluminum Oxide [\(Al_2O_3\)] \(\to\) forms Aluminate.
- Zinc Oxide [\(ZnO\)] \(\to\) forms Zincate.
Remembering these two formulas is extremely useful.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question defines amphoteric oxides as those metal oxides that can exhibit both acidic and basic characteristics, reacting with both acids and bases to produce salt and water. We need to select the option that lists two such amphoteric oxides.

Step 2: Key Formula or Approach:
Analyze the chemical reactivity of aluminum oxide (\(Al_2O_3\)) and zinc oxide (\(ZnO\)) with a strong acid (like \(HCl\)) and a strong base (like \(NaOH\)).

Step 3: Detailed Explanation:

• Most metal oxides are basic and react only with acids. However, some metal oxides can react with both acids and bases. These are called amphoteric oxides.

• Aluminum Oxide (\(Al_2O_3\)):
- Reacts with acid (\(HCl\)):
\[ Al_2O_3\text{(s)} + 6HCl\text{(aq)} \to 2AlCl_3\text{(aq)} + 3H_2O\text{(l)} \] - Reacts with base (\(NaOH\)):
\[ Al_2O_3\text{(s)} + 2NaOH\text{(aq)} \to 2NaAlO_2\text{(aq) [Sodium aluminate]} + H_2O\text{(l)} \]

• Zinc Oxide (\(ZnO\)):
- Reacts with acid (\(HCl\)):
\[ ZnO\text{(s)} + 2HCl\text{(aq)} \to ZnCl_2\text{(aq)} + H_2O\text{(l)} \] - Reacts with base (\(NaOH\)):
\[ ZnO\text{(s)} + 2NaOH\text{(aq)} \to Na_2ZnO_2\text{(aq) [Sodium zincate]} + H_2O\text{(l)} \]

• Both \(Al_2O_3\) and \(ZnO\) show this dual chemical behavior, making them classic examples of amphoteric oxides.


Step 4: Final Answer:
The examples of amphoteric oxides are \(Al_2O_3\) and \(ZnO\), matching Option (B).