CIE iGCSE Co-ordinated Sciences-C7.2 Oxides- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-C7.2 Oxides – Study Notes
CIE iGCSE Co-ordinated Sciences-C7.2 Oxides – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Classification of Oxides
Oxides can be classified as acidic or basic, depending on whether they are formed by non-metals or metals.
Acidic Oxides
- Acidic oxides are usually non-metal oxides.
- They dissolve in water to form acids, or react with bases/alkalis to form salts.
Examples:
\( \text{SO}_2 \), \( \text{CO}_2 \)
\( \text{SO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_3 \)
\( \text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3 \)
Example
Why is carbon dioxide classified as an acidic oxide?
▶️Answer/Explanation
\( \text{CO}_2 \) is a non-metal oxide. It dissolves in water to form carbonic acid:
\( \text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3 \).
Therefore, it is an acidic oxide.
Example
Explain why sulfur dioxide is considered an acidic oxide.
▶️Answer/Explanation
\( \text{SO}_2 \) is a non-metal oxide. It reacts with water to form sulfurous acid:
\( \text{SO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_3 \).
Hence, it is classified as an acidic oxide.
Basic Oxides
- Basic oxides are usually metal oxides.
- They react with acids to form salts and water.
Examples:
\( \text{CuO} \), \( \text{CaO} \)
\( \text{CuO} + \text{H}_2\text{SO}_4 \rightarrow \text{CuSO}_4 + \text{H}_2\text{O} \)
\( \text{CaO} + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} \)
Example
Why is copper(II) oxide considered a basic oxide?
▶️Answer/Explanation
\( \text{CuO} \) is a metal oxide. It reacts with acids such as sulfuric acid to form a salt and water:
\( \text{CuO} + \text{H}_2\text{SO}_4 \rightarrow \text{CuSO}_4 + \text{H}_2\text{O} \).
Therefore, it is a basic oxide.
Example
Explain why calcium oxide is classified as a basic oxide.
▶️Answer/Explanation
\( \text{CaO} \) is a metal oxide. It reacts with acids like hydrochloric acid to form calcium chloride and water:
\( \text{CaO} + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} \).
Thus, it is a basic oxide.
Amphoteric Oxides
Amphoteric oxides are oxides that can react with both acids and bases to form a salt and water. They usually come from metals that are close to the metalloid region of the periodic table (e.g., aluminium and zinc).
General Reactions:
With an acid:
\( \text{Amphoteric oxide} + \text{Acid} \rightarrow \text{Salt} + \text{H}_2\text{O} \)
With a base:
\( \text{Amphoteric oxide} + \text{Base} \rightarrow \text{Salt} + \text{H}_2\text{O} \)
Examples:
Aluminium oxide (\( \text{Al}_2\text{O}_3 \)) reacts with hydrochloric acid and sodium hydroxide:
With acid:
\( \text{Al}_2\text{O}_3 + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2\text{O} \)
With base:
\( \text{Al}_2\text{O}_3 + 2\text{NaOH} + 3\text{H}_2\text{O} \rightarrow 2\text{NaAl(OH)}_4 \)
Example
Explain why aluminium oxide is classified as an amphoteric oxide.
▶️Answer/Explanation
Aluminium oxide reacts with acids to form salts like aluminium chloride:
\( \text{Al}_2\text{O}_3 + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2\text{O} \)
It also reacts with bases to form aluminate salts:
\( \text{Al}_2\text{O}_3 + 2\text{NaOH} + 3\text{H}_2\text{O} \rightarrow 2\text{NaAl(OH)}_4 \)
Therefore, it is amphoteric because it can react with both acids and bases.
Example
Write the products when zinc oxide reacts with sulfuric acid and with sodium hydroxide.
▶️Answer/Explanation
With acid:
\( \text{ZnO} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2\text{O} \)
With base:
\( \text{ZnO} + 2\text{NaOH} + \text{H}_2\text{O} \rightarrow \text{Na}_2\text{[Zn(OH)_4]} \)
Zinc oxide reacts with both acids and bases, so it is an amphoteric oxide.
Classification of Al2O3 and ZnO as Amphoteric Oxides
Aluminium oxide (\( \text{Al}_2\text{O}_3 \)) and zinc oxide (\( \text{ZnO} \)) are classified as amphoteric oxides because they can react with both acids and bases to form a salt and water.
Reactions of Al2O3:
With acid: \( \text{Al}_2\text{O}_3 + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2\text{O} \)
With base: \( \text{Al}_2\text{O}_3 + 2\text{NaOH} + 3\text{H}_2\text{O} \rightarrow 2\text{NaAl(OH)}_4 \)
Reactions of ZnO:
With acid: \( \text{ZnO} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2\text{O} \)
With base: \(\text{ZnO} + 2\text{NaOH} + \text{H}_2\text{O} \;\rightarrow\; \text{Na}_2[\text{Zn(OH)}_4]\)
Example
Explain why aluminium oxide is amphoteric.
▶️Answer/Explanation
Aluminium oxide reacts with acids to form salts like aluminium chloride and with bases to form aluminates:
\( \text{Al}_2\text{O}_3 + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2\text{O} \)
\( \text{Al}_2\text{O}_3 + 2\text{NaOH} + 3\text{H}_2\text{O} \rightarrow 2\text{NaAl(OH)}_4 \)
This dual behaviour makes it amphoteric.
Example
Why is zinc oxide classified as an amphoteric oxide?
▶️Answer/Explanation
Zinc oxide reacts with acids to form salts and with bases to form complex zincates:
\( \text{ZnO} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2\text{O} \)
\( \text{ZnO} + 2\text{NaOH} + \text{H}_2\text{O} \rightarrow \text{Na}_2\text{[Zn(OH)_4]} \)
Because it can react with both acids and bases, ZnO is amphoteric.