Amphoteric Oxides
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Amphoteric Oxides
Sep 26, 2022, 16:45 IST
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What are Amphoteric Oxides?
Amphoteric Oxides are the oxides that act as acidic and basic oxides. It has features of acidic oxide as well as basic oxides that neutralize both acids and bases.
Amphoteric oxides generally dissolve in water to form alkaline solutions. The Alkaline solutions consist of hydroxide ions. Therefore, aluminum oxide (Al 2 O 3 ) reacts with hydrochloric acid to form aluminum chloride and water. The sodium hydroxide solution forms water and sodium aluminate (NaAlO 2 ). Other examples of amphoteric oxides include ZnO, SnO, and PbO.
Identification of Amphoteric Oxides
Oxides are compounds of an metals or nonmetals with oxygen. There are 4 types of oxides. Amphoteric oxides are categorized as metal oxides that react with both the acids and bases to form water and salts. Amphoteric oxides, among many others, include zinc oxide and lead oxide. Examples include amino acids and proteins with amine and carboxylic acid classes and molecules that can self-ionize, such as water.
Amphoteric oxides are oxygen compounds that exhibit both acidic and basic properties. These oxides undergo a neutralization reaction to form water and salt when they react with acid. This demonstrates the basic properties of compounds. Similarly, alkali reacts to form salt and water, which has an acidic property. Example: aluminum oxide.
All oxides can be formed by heating the element in oxygen. By reacting aqueous solutions of metal trihalides with hydroxide, oxides are obtained in hydrated form. Descending in the group, there is a transition from acid oxides to amphoteric to basic oxides due to the increasing metallic character of the respective elements.
Oxides of group 13 elements
| Oxides | Properties |
| B 2 O 3 | Weakly acidic |
| Al 2 O 3 | Amphoteric |
| Ga 2 O 3 | Amphoteric |
| In 2 O 3 | Weakly base |
| Tl 2 O 3 | Basic, oxidizing |
Amphoteric Oxides Examples
The term amphoteric means both acid and base. Amphoteric oxides have both acidic and basic properties. Examples are aluminum and zinc oxides. When reacting with acids, they form salts. They also react with alkalis to form complex salts.
Examples:
ZnO(s) + 2HNO 3 (aq) → Zn(NO 3 ) 2 (aq) + H 2 O(l)
ZnO(s) + 2NaOH(aq) → Na 2 ZnO 2 (aq) + H 2 O(l)
Al 2 O 3 (s) + 6HCl(aq) → 2AlCl 3 (aq) + 3H 2 O(l)
Al 2 O 3 (s) + 2NaOH(aq) → 2NaAlO 2 (aq) + H 2 O(l)
Both the Zincates and aluminates have the ending -ate to indicate that their ions are complex ions containing oxygen - rather like sulfates, carbonates, and nitrates, meaning that the ions are ZnO 2 2- and the aluminate ions are AlO 2- . The ions are written as Zn(OH) 4 2- and Al(OH) 4- . Note that sodium zincate and aluminate are soluble in water.
Amphoteric Oxides in Periodic Table
In a given period, oxides progress from strongly basic, weakly basic, amphoteric, and weakly acidic to strongly acidic, e.g., Na 2 O, MgO, Al 2 O 3 , P 4 O 10 , SO 3 , and Cl 2 O 7 . Acidity increases with increasing oxidation state, e.g., MnO < Mn 2 O 3 < Mn 2 O 7 .
There is a trend in the acidity of oxides in the periodic table. Generally, the period's trend is basic → amphoteric, → acidic. The following table shows the trend of oxide acidity for period 3.
| Na 2 O | MgO | Al 2 O 3 | SiO 2 | P 4 O 18 | SO 2 | Cl 2 O 7 |
| Strongly basic | Basic | Amphoteric | Weakly acidic | Acidic | Acidic | Strongly acidic |
The basic oxides are found near the bottom of groups I and II. Basicity tends to increase in the periodic group. For group V, the acidities of the oxides are NO 2 (acidic), P 2 O 3 (acidic), and As 2 O 3 (amphoteric). Sb 2 O 3 (amphoteric), Bi 2 O 3 (basic).
In the main groups of elements, the basicity of oxides increases with an increasing atomic number in the group, e.g., BeO < MgO < CaO < SrO < BaO, although the trend is reversed in the later groups of transition elements.
Frequently Asked Question (FAQs)
Q1. How do you know if the oxide is amphoteric?
Ans. You may say that if an oxide reacts with acid and forms a salt, or if an oxide reacts with a base and forms a salt, then you can say that it is an amphoteric oxide.
Q2. Which elements form amphoteric oxides?
Ans. Metals such as zinc, copper, tin, lead, aluminum, and beryllium form amphoteric oxides or hydroxides.
Q3. How many oxides are amphoteric in nature?
Ans. Aluminum oxide, beryllium oxide, tin oxide, and zinc oxide all are amphoteric.
Q4. Is CO 2 amphoteric?
Ans. No, CO 2 is acidic in nature.
Q5. Is NaOH amphoteric?
Ans. No. Alkali metals' hydroxides, and oxides do not show amphoteric properties. Therefore NaOH is not an amphoteric compound.
