Science (086) — AI-generated practice question

Reaction with hydrochloric acid (HCl):

$$\text{Al}_2\text{O}_3 + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2\text{O}$$

Reaction with sodium hydroxide (NaOH):

$$\text{Al}_2\text{O}_3 + 2\text{NaOH} \rightarrow 2\text{NaAlO}_2 + \text{H}_2\text{O}$$

(Sodium aluminate)

Property demonstrated:
Since aluminium oxide reacts with both acids and bases to produce salt and water, it behaves as both a basic oxide (with HCl) and an acidic oxide (with NaOH). This property is called amphoteric nature. Aluminium oxide is therefore an amphoteric oxide.

Source: Chapter 2, Section 2.1.5 & 2.1.6

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• Examiners expect both balanced equations (1 mark each) and a clear explanation of the amphoteric property (1 mark).
• The key term to use is amphoteric — an oxide that reacts with both acids and bases. This is the exact terminology CBSE expects.
• Note that with NaOH, the product is sodium aluminate (NaAlO₂), not aluminium hydroxide — make sure to write the correct product.
• Don't forget: metallic oxides are basic oxides, but Al₂O₃ is an exception because it also behaves as an acidic oxide, hence amphoteric.