Among the following oxides of p-block elements, the number of oxides having amphoteric nature is: \[\text{Cl}_2\text{O}_7, \, \text{CO}, \, \text{PbO}_2, \, \text{N}_2\text{O}, \, \text{NO}, \, \text{Al}_2\text{O}_3, \, \text{SiO}_2, \, \text{N}_2\text{O}_5, \, \text{SnO}_2\]
Correct Answer: 3
Approach Solution - 1
The problem asks to identify the amphoteric oxides from a given list of p-block element oxides and determine their total number.
Concept Used:
The nature of an oxide (acidic, basic, amphoteric, or neutral) depends on the element and its oxidation state. The classification is as follows:
- Acidic Oxides: These are typically oxides of non-metals (e.g., \( \text{SO}_2, \text{CO}_2, \text{Cl}_2\text{O}_7 \)). They react with bases to form salt and water. The acidic character increases with the increasing oxidation state of the central non-metal.
- Basic Oxides: These are oxides of metals (e.g., \( \text{Na}_2\text{O}, \text{CaO} \)). They react with acids to form salt and water.
- Amphoteric Oxides: These oxides exhibit both acidic and basic properties. They react with both acids and bases to form salt and water. Oxides of elements near the metal-nonmetal boundary in the periodic table, such as Al, Zn, Sn, and Pb, are typically amphoteric.
- Neutral Oxides: These oxides do not react with either acids or bases. Common examples are \( \text{CO}, \text{NO}, \) and \( \text{N}_2\text{O} \).
Step-by-Step Solution:
We will classify each oxide from the given list:
Step 1: Classify each oxide.
- \( \text{Cl}_2\text{O}_7 \) (Dichlorine heptoxide): Chlorine is a non-metal in its highest oxidation state (+7). This is a strongly acidic oxide. It is the anhydride of perchloric acid (\( \text{HClO}_4 \)).
- \( \text{CO} \) (Carbon monoxide): This is a well-known neutral oxide. It does not exhibit acidic or basic properties.
- \( \text{PbO}_2 \) (Lead(IV) oxide): Lead is a metal. Its oxides are known to be amphoteric. It reacts with both acids and bases. For example:
With acid: \( 2\text{PbO}_2 + 2\text{H}_2\text{SO}_4 \rightarrow 2\text{PbSO}_4 + 2\text{H}_2\text{O} + \text{O}_2 \)
With base: \( \text{PbO}_2 + 2\text{NaOH} + 2\text{H}_2\text{O} \rightarrow \text{Na}_2[\text{Pb(OH)}_6] \) (Sodium plumbate)
Thus, it is amphoteric. - \( \text{N}_2\text{O} \) (Dinitrogen monoxide): This is another example of a neutral oxide.
- \( \text{NO} \) (Nitrogen monoxide): This is also a neutral oxide.
- \( \text{Al}_2\text{O}_3 \) (Aluminum oxide): Aluminum is a metalloid-like metal, and its oxide is a classic example of an amphoteric substance. It reacts with both acids and bases:
With acid: \( \text{Al}_2\text{O}_3 + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2\text{O} \)
With base: \( \text{Al}_2\text{O}_3 + 2\text{NaOH} + 3\text{H}_2\text{O} \rightarrow 2\text{Na}[\text{Al(OH)}_4] \) (Sodium aluminate)
Thus, it is amphoteric. - \( \text{SiO}_2 \) (Silicon dioxide): Silicon is a metalloid. Its oxide is acidic. It reacts with strong bases to form silicates but does not react with most acids (except hydrofluoric acid).
- \( \text{N}_2\text{O}_5 \) (Dinitrogen pentoxide): Nitrogen is a non-metal in a high oxidation state (+5). This is a strongly acidic oxide, being the anhydride of nitric acid (\( \text{HNO}_3 \)).
- \( \text{SnO}_2 \) (Tin(IV) oxide): Tin is a metal whose oxides are amphoteric. It reacts with both strong acids and strong bases:
With acid: \( \text{SnO}_2 + 4\text{HCl} \rightarrow \text{SnCl}_4 + 2\text{H}_2\text{O} \)
With base: \( \text{SnO}_2 + 2\text{NaOH} \rightarrow \text{Na}_2\text{SnO}_3 + \text{H}_2\text{O} \) (Sodium stannate)
Thus, it is amphoteric.
Step 2: Count the amphoteric oxides.
From the classification above, the oxides that are amphoteric in nature are:
- \( \text{PbO}_2 \)
- \( \text{Al}_2\text{O}_3 \)
- \( \text{SnO}_2 \)
Counting these oxides, we find there are a total of three.
Final Result:
The number of oxides having amphoteric nature in the given list is 3.
Approach Solution -2
Acidic oxide: Cl2O7, SiO2, N2O5
Neutral oxide: CO, NO, N2O
Amphoteric oxide: Al2O3, SnO2, PbO2
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