11.05 Metal Oxides and Non-Metal Oxides
Classification of Oxides
- Non-Metal Oxides:
- Acidic Oxides:
- React with bases to form salts and dissolve in water to form acidic solutions.
- Examples: CO₂, SO₂, SO₃, NO₂, P₂O₅, SiO₂.
- Neutral Oxides:
- Do not react with acids or bases.
- Examples: H₂O, CO, NO.
- Acidic Oxides:
- Metal Oxides:
- Basic Oxides:
- React with acids to neutralize them, forming salts and water.
- Examples: CaO, MgO, CuO, K₂O, Na₂O, FeO, Fe₂O₃.
- Amphoteric Oxides:
- React with both acids and alkalis to form salts and water.
- Examples: ZnO, Al₂O₃.
- Basic Oxides:
Key Properties
- Acidic Oxides:
- Produced by burning non-metals in oxygen.
- Dissolve in water to form acidic solutions (e.g., sulfur dioxide and carbon dioxide turn blue litmus red).
- Example reactions:
- Sulfur burning in oxygen: S(s)+O2(g)→SO2(g)
- Carbon burning in oxygen: C(s)+O2(g)→CO2(g)
- Basic Oxides:
- Produced by burning metals in oxygen.
- Dissolve in water to form alkaline solutions (e.g., magnesium oxide turns red litmus blue).
- Example reactions:
- Magnesium burning in oxygen:
2Mg(s) + O2(g) → 2MgO(s) - Sodium burning in oxygen:
4Na(s) + O2(g) → 2Na2O(s)
- Magnesium burning in oxygen:
- Neutral Oxides:
- Do not react with acids or alkalis.
- Examples: H₂O, CO, NO.
- Amphoteric Oxides:
- Exhibit both acidic and basic properties by reacting with acids and alkalis to form salts and water.
- Example reactions:
- Zinc oxide with hydrochloric acid:
ZnO(s) + 2HCl(aq) → ZnCl2(aq) + H2O(l) - Zinc oxide with sodium hydroxide:
ZnO(s) + 2NaOH(aq) → Na2ZnO2(aq) + H2O(l)
- Zinc oxide with hydrochloric acid:
Reactions of Elements with Oxygen
| Element | Product | Appearance | Effect of Adding Water |
|---|---|---|---|
| Non-Metals | |||
| Sulfur | Sulfur dioxide (SO₂) | Burns with a bright blue flame | Dissolves, turns litmus red |
| Phosphorus | Phosphorus pentoxide (P₄O₁₀) | Burns with a yellow flame | Dissolves, turns litmus red |
| Carbon | Carbon dioxide (CO₂) | Glows red | Dissolves slightly, turns litmus red |
| Metals | |||
| Sodium | Sodium oxide (Na₂O) | Burns with a yellow flame | Dissolves, turns litmus blue |
| Magnesium | Magnesium oxide (MgO) | Burns with a bright white flame | Dissolves slightly, turns litmus blue |
| Calcium | Calcium oxide (CaO) | Burns with a red flame | Dissolves, turns litmus blue |
| Iron | Iron(III) oxide (Fe₂O₃) | Burns with yellow sparks | Insoluble |
| Copper | Copper(II) oxide (CuO) | Turns black | Insoluble |
Environmental Impacts
- Acid Rain:
- Caused by acidic oxides like SO₂ and NOₓ released during the combustion of fossil fuels.
- Acid rain has a pH between 4.2 and 4.4 (normal rain: pH ~5.6).
- Effects:
- Damages trees, plants, and aquatic life.
- Erodes buildings and structures.
- Sources of Acidic Oxides:
- Combustion of sulfur-contaminated fossil fuels.
- Vehicle emissions releasing nitrogen oxides (NO and NO₂).
Definitions
- Acidic Oxide: Non-metal oxide that reacts with bases to form salts and dissolves in water to form acidic solutions.
- Basic Oxide: Metal oxide that reacts with acids to neutralize them and dissolves in water to form alkaline solutions.
- Neutral Oxide: Oxide that does not react with acids or bases (e.g., CO, H₂O).
- Amphoteric Oxide: Metal oxide that reacts with both acids and alkalis to form salts and water.
Summary Diagram
| Type of Oxide | Examples |
|---|---|
| Acidic Oxides | CO₂, SO₂, SO₃, NO₂, P₂O₅, SiO₂ |
| Basic Oxides | CaO, MgO, CuO, K₂O, Na₂O, FeO, Fe₂O₃ |
| Neutral Oxides | H₂O, CO, NO |
| Amphoteric Oxides | ZnO, Al₂O₃ |
Example Questions and Answers
- What are acidic oxides? Give examples.
- Acidic oxides are oxides of non-metals that react with bases and dissolve in water to form acidic solutions.
Examples: CO₂, SO₂, SO₃.
- Acidic oxides are oxides of non-metals that react with bases and dissolve in water to form acidic solutions.
- Define an amphoteric oxide and provide examples.
- Amphoteric oxides react with both acids and alkalis to form salts and water.
Examples: ZnO, Al₂O₃.
- Amphoteric oxides react with both acids and alkalis to form salts and water.
- Write balanced equations for the reaction of aluminum oxide with hydrochloric acid and sodium hydroxide.
- With hydrochloric acid:
Al2O3(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2O(l) - With sodium hydroxide:
Al2O3(s) + 2NaOH(aq) → 2NaAlO2(aq) + H2O(l)
- With hydrochloric acid:
Quizzes
Quiz 1