Which of the following oxides is amphoteric in character?
(a) SnO2
(b) SiO2
(c) CO2
(d) CaO

Q: Why is SiO2 not considered amphoteric?

While SiO2 is an oxide of a metalloid, it is predominantly weakly acidic. It reacts with strong bases like NaOH to form sodium silicate, but it does not react with most acids (except HF, which is a specific reaction driven by the high bond energy of Si-F). Therefore, it lacks the dual reactivity required to be amphoteric.

Q: Are all oxides of Group 14 elements amphoteric?

No. The nature of oxides changes down the group. CO2 and SiO2 are acidic, GeO2 is amphoteric (but more acidic), while SnO2 and PbO2 are distinctly amphoteric. This reflects the transition from non-metallic to metallic character down the group.

Q: What exactly is sodium stannate?

Sodium stannate (Na2SnO3) is the salt formed when tin dioxide acts as an acid and reacts with the base sodium hydroxide. In aqueous solution, it often exists as the hexahydroxostannate(IV) complex, Na2[Sn(OH)6].

Q: How can I easily remember which metals form amphoteric oxides?

A common mnemonic used by students is 'Zindagi (Zn) Alag (Al) Suno (Sn) Prabhu (Pb)'. These four metals—Zinc, Aluminum, Tin, and Lead—are the most frequently tested examples of elements that form amphoteric oxides.

Q: Does the oxidation state of the metal affect whether its oxide is amphoteric?

Yes, it can. Generally, as the oxidation state of a metal increases, the acidic character of its oxide increases. For tin, both SnO (+2) and SnO2 (+4) are amphoteric, but SnO2 is slightly more acidic than SnO.

Question

Which of the following oxides is amphoteric in character?

Options:

(A) $	ext{SnO}_2$

(B) $	ext{SiO}_2$

(C) $	ext{CO}_2$

(D) $	ext{CaO}$

Sigma Percentile · Accepted Answer

### The Dual Personality of Amphoteric Oxides

In the fascinating world of inorganic chemistry, oxides generally fall into distinct categories based on their chemical behavior: acidic, basic, or neutral. However, there is a special class of oxides that refuse to be boxed into just one category. These are the **amphoteric oxides**.

An amphoteric oxide is a chemical chameleon. It possesses a dual personality, allowing it to react with both acids and bases to produce salt and water. This unique behavior is typically observed in oxides of elements that lie near the boundary between metals and non-metals in the periodic table, or metals with intermediate electronegativity.

### Analyzing the Suspects

Let's evaluate the given options to identify the amphoteric culprit:

1. **$	ext{CO}_2$ (Carbon Dioxide):** Carbon is a quintessential non-metal. Non-metal oxides are generally acidic. When dissolved in water, $	ext{CO}_2$ forms carbonic acid ($	ext{H}_2	ext{CO}_3$).

2. **$	ext{SiO}_2$ (Silicon Dioxide):** Silicon is a metalloid, but its dioxide is weakly acidic. It reacts with strong bases like $	ext{NaOH}$ to form silicates, but it generally does not react with acids (with the notable exception of hydrofluoric acid, $	ext{HF}$).

3. **$	ext{CaO}$ (Calcium Oxide):** Calcium is an alkaline earth metal (Group 2). Metals on the far left of the periodic table form strongly basic oxides. $	ext{CaO}$ reacts vigorously with water to form calcium hydroxide, a strong base.

4. **$	ext{SnO}_2$ (Tin Dioxide):** Tin is a Group 14 metal. Elements like Tin ($	ext{Sn}$), Lead ($	ext{Pb}$), Zinc ($	ext{Zn}$), and Aluminum ($	ext{Al}$) are famous for forming amphoteric oxides. Let's prove this by looking at its reactions.

### The Chemical Proof

To confirm that $	ext{SnO}_2$ is indeed amphoteric, we must observe it reacting as both a base and an acid.

**Acting as a Base:**
When treated with a strong acid like hydrochloric acid, $	ext{SnO}_2$ neutralizes it to form a salt (tin tetrachloride) and water.

$$	ext{SnO}_2 + 4	ext{HCl} ightarrow 	ext{SnCl}_4 + 2	ext{H}_2	ext{O}$$

**Acting as an Acid:**
Conversely, when treated with a strong base like sodium hydroxide, $	ext{SnO}_2$ acts as an acid, forming a complex salt known as sodium stannate.

$$	ext{SnO}_2 + 2	ext{NaOH} ightarrow 	ext{Na}_2	ext{SnO}_3 + 	ext{H}_2	ext{O}$$

### The Final Verdict

Because $	ext{SnO}_2$ successfully reacts with both a strong acid and a strong base, it definitively proves its amphoteric nature. Understanding these periodic trends and the specific behavior of borderline elements is a crucial skill for mastering p-block chemistry.

Animated Solution for Chemistry - s and p-Block Elements: Which of the following oxides is amphoteric in character?

Select Answer:

Visualized Solution

Definition of Amphoteric Oxides

Analyzing the Given Oxides

Reaction with Acid

Reaction with Base

Final Conclusion

The Sigma Insight: Group 14 Elements

The Dual Personality of Amphoteric Oxides

Analyzing the Suspects

The Chemical Proof

The Final Verdict

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