Table of Common Amphoteric Oxides with Formulas and Groups
Amphoteric oxides are essential in chemistry and help students understand various practical and theoretical applications related to oxides, acid-base behavior, and periodic trends. Grasping this concept is particularly useful for students preparing for board exams, NEET, and JEE.
What is Amphoteric Oxides in Chemistry?
An amphoteric oxide refers to an oxide that can react both as an acid and a base. This means it will react with acids to form salt and water (showing basic behavior), and with bases to give salt and water (displaying acidic behavior). This concept appears in chapters related to acid-base chemistry, periodic properties, and the reactivity of metals and non-metals, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
There is no single molecular formula for all amphoteric oxides, as this category includes several specific compounds. Examples include ZnO (zinc oxide), Al2O3 (aluminium oxide), PbO (lead(II) oxide), and SnO (tin(II) oxide). Each consists of a metal bonded to oxygen and is classified under the broader group of metallic oxides with dual chemical behavior.
Preparation and Synthesis Methods
Amphoteric oxides are generally prepared by:
- Direct combustion of metals in oxygen (e.g., burning zinc gives ZnO, aluminium gives Al2O3)
- Calcination of metal carbonate or hydroxide (e.g., heating ZnCO3 yields ZnO)
- In industry, bauxite ore (Al2O3.2H2O) is processed to extract aluminium oxide using the Bayer process.
These oxides can also be synthesized through the thermal decomposition of nitrates or hydroxides.
Physical Properties of Amphoteric Oxides
Amphoteric oxides are usually solid, non-volatile substances with high melting and boiling points. Many are white (ZnO) or colorless (Al2O3 crystal form), insoluble in water (except in acidic or basic solutions), and have stable, strong crystal lattice structures.
Chemical Properties and Reactions
The defining chemical property is dual reactivity:
1. Reaction with acids (behaves as a base)
2. Reaction with bases (behaves as an acid)
Examples:
ZnO + 2HCl → ZnCl2 + H2O (with acid)
ZnO + 2NaOH + H2O → Na2[Zn(OH)4] (with base)
Other typical reactions include forming complex salts (aluminates, zincates) in strong alkali and forming chlorides/sulfates in strong acid.
Frequent Related Errors
- Confusing amphoteric oxides with neutral oxides such as CO or N2O.
- Writing incomplete or improperly balanced reactions with acids or bases.
- Assuming all metal oxides are basic or all non-metal oxides are acidic.
- Overlooking the true dual nature in lab questions or exams; not citing both acid and base reactions as proof.
Uses of Amphoteric Oxides in Real Life
Amphoteric oxides have important real-life applications. For example, aluminium oxide (Al2O3) is used in the production of aluminium metal, as an abrasive in sandpaper, and as a catalyst. Zinc oxide (ZnO) is used in sunscreen, cosmetics, medicinal ointments, rubber manufacturing, and ceramics. Lead(II) oxide (PbO) is key in making specialized glass and ceramics. These oxides also contribute to environmental and extraction processes due to their unique chemical behavior.
Relevance in Competitive Exams
Students preparing for NEET, JEE, and Olympiads should be familiar with amphoteric oxides, as questions often ask for identification, reactions, comparison with acidic/basic oxides, and periodic trends. Memorizing examples, reactions, and behavior is a common MCQ/short answer need.
Relation with Other Chemistry Concepts
Amphoteric oxides are closely related to topics such as acidic oxides and basic oxides, as well as the study of oxide chemistry and metallurgy. Understanding this aids students in building a strong foundation for chemical classification, reactivity series, and extraction of metals.
Step-by-Step Reaction Example
1. Identify the amphoteric oxide to be tested (e.g., ZnO)2. Write the reaction with acid: ZnO + 2HCl → ZnCl2 + H2O
3. Write the reaction with a base: ZnO + 2NaOH + H2O → Na2[Zn(OH)4]
4. State that in both cases, ZnO reacts to give salt and water—proving amphoterism.
Lab or Experimental Tips
Remember amphoteric oxides by the rule "They react both ways," or use memory tricks like "ZnAlPbSn—amphoteric run!" Vedantu educators often suggest confirming amphoterism by performing both acid and base tests in practical exams. Always balance your equations to get full marks.
Try This Yourself
- List three amphoteric oxides and write their reactions with hydrochloric acid and sodium hydroxide.
- Check if BeO is amphoteric or just basic.
- Compare the behavior of Al2O3 with CO2 in chemical tests.
- Classify PbO as acidic, basic, or amphoteric based on its reactions.
Final Wrap-Up
We explored amphoteric oxides—their types, properties, dual reactivity, practical uses, and exam importance. Amphoteric oxides build a bridge between the concepts of acids, bases, and the periodic nature of elements. For in-depth guidance and revision resources, explore topic pages and live classes on Vedantu.
FAQs on Amphoteric Oxides – Definition, Examples, Properties & Reactions
1. What are amphoteric oxides?
Amphoteric oxides are chemical compounds that react with both acids and bases to form salt and water. They exhibit dual acidic and basic properties. Common examples include aluminum oxide (Al2O3) and zinc oxide (ZnO).
2. Are Al2O3 and ZnO examples of amphoteric oxides?
Yes, both aluminum oxide (Al2O3) and zinc oxide (ZnO) are classic examples of amphoteric oxides.
3. How do you identify an amphoteric oxide?
An oxide is identified as amphoteric if it reacts with both acids and bases to produce salt and water. This dual reactivity is demonstrated through balanced chemical equations showing reactions with both an acid (e.g., HCl) and a base (e.g., NaOH).
4. What are five examples of amphoteric oxides?
Five common examples of amphoteric oxides include: Al2O3, ZnO, PbO, SnO, and Cr2O3.
5. Why is ZnO called amphoteric?
Zinc oxide (ZnO) is called amphoteric because it reacts with acids to form zinc salts and with bases to form zincates, demonstrating both acidic and basic behavior.
6. Can non-metal oxides ever be amphoteric?
Very rarely. Most amphoteric oxides are metallic oxides. Some metalloids might exhibit weak amphoteric properties.
7. Are all d-block metal oxides amphoteric?
No. Only certain d-block oxides, such as Cr2O3, show clear amphoteric behavior. Many are basic or neutral.
8. Does amphoterism depend on the oxidation state?
Yes, the oxidation state of the metal significantly influences whether an oxide exhibits acidic, basic, or amphoteric character.
9. How are amphoteric oxides useful in metallurgical extraction?
Amphoteric oxides are useful in metallurgical extraction because their unique reactivity allows for selective leaching and separation of metals during refining processes.
10. What is a quick trick to recall amphoteric oxides for exams?
A helpful mnemonic is: "Zn, Al, Pb, Sn—amphoteric run!" (Zinc, Aluminum, Lead, Tin).
11. What are some real-world applications of amphoteric oxides?
Aluminum oxide (Al2O3) is used in materials like ceramics and as a catalyst. Zinc oxide (ZnO) finds applications in sunscreen, pigments, and rubber production. Lead oxide (PbO) is used in glass manufacturing.
12. What is the difference between amphoteric and amphiprotic?
Amphoteric substances can act as both acids and bases. Amphiprotic substances can both donate and accept protons (H+ ions). All amphiprotic substances are amphoteric, but not all amphoteric substances are amphiprotic.
