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An amphoteric oxide is a compound that may function as both an acid and a base. Oxides can be acidic, basic, amphoteric, or neutral in nature.
- Amphoteric oxides are metal oxides that react with both acids and bases to generate salts and water.
- The property of having both acidic and basic oxides is known as amphoterism.
- Non-metallic oxides are often acidic, whereas metallic oxides are basic.
- Some non-metallic oxides are neutral, whereas others are metallic or semi-metallic oxides.
- There are a few exceptions to these broad generalizations.
- Hydrochloric acid interacts with copper oxide.
- ZnO, SnO and PbO are some common examples of amphoteric oxide.
Key Terms: Amphoteric Oxides, Acids and Bases, Salt, Water, Hydrochloric Acid, Oxides, Periodic Table, Aluminium Amphoteric Oxide, Sodium Hydroxide, Sodium Aluminate, Oxygen
What is Amphoteric Oxide?
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Amphoteric oxides are oxides that may be both basic and acidic. These oxides have the properties of both acidic and basic oxides, allowing them to neutralise both acids and bases.
- Alkaline solutions are formed when amphoteric oxides dissolve in water.
- Hydroxide ions are present in alkaline liquids.
As a result, when aluminium oxide (which is Al2O3) interacts with hydrochloric acid, it produces water and aluminium chloride. Aluminium oxide is classified as an amphoteric oxide.
- It generates water and sodium aluminate (NaAlO2) from a sodium hydroxide solution.
- Al2O3 is the formula for amphoteric oxide.
When this oxide reacts with a base, it will form salt and water, which hints at the acidic behaviour of the oxide. On the other hand, when this oxide reacts with an acid, it will again form salt and water, indicating the basic behaviour of the amphoteric oxide.
Examples of Amphoteric OxidesExample: Examples of Amphoteric Oxides
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Amphoteric oxides
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How to Identify Amphoteric Oxides?
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Oxides are metals or non-metals that have been combined with oxygen. There are four different kinds of oxide. Amphoteric oxides are metal oxides that react with both acids and bases to produce water and salts.
- Zinc oxide and lead oxide are two examples of amphoteric oxides.
- Proteins and amino acids are examples of carboxylic acids, amines, and molecules that may self-ionize, such as water.
Amphoteric oxides are oxygen compounds that exhibit both basic and acidic properties. When these oxides combine with acid, they undergo a neutralization process that produces water and salt.
- This section outlines the compounds' key characteristics.
- Similarly, the alkali responds to the creation of salt and water, exhibiting an acidic characteristic.
- An oxide of aluminium is one example.
By heating the element in oxygen, all of the oxides may be produced. The hydrated oxides are formed by the interaction of aqueous solutions of metal trihalides with hydroxide.
- Due to the increased metallic nature of the elements involved, there is a shift from acidic oxides to amphoteric to basic as one moves down the group.
Oxides of the Group 13 elements
| Oxides | Properties |
|---|---|
| B2O3 | Weakly acidic |
| Al2O3 | Amphoteric |
| Ga2O3 | Amphoteric |
| In2O3 | Weakly base |
| Tl2O3 | Basic, oxidizing |
Amphoteric Oxides in Periodic Table
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During a particular time period, the oxides go from strongly basic to weakly basic, amphoteric, and weakly acidic to strongly acidic for example, Na2O, MgO, Al2O3, P4O10, SO3, and Cl2O7.
- Acidity increases with increasing oxidation states, for example, MnO, Mn2O3, and Mn2O7.
- The periodic table shows a trend in oxide acidity.
- The overall tendency over time is basic amphoteric acidic.
- The basicity of oxides increases with increasing atomic number down the group in the major groups of elements.
- Some common examples include BeO MgO CaO SrO BaO.
- However, this tendency is reversed in later transition element groups.
The trend in oxide acidity during period three is seen in the table below.
| Compound | Data |
|---|---|
| Na2O | Strongly basic |
| MgO | Basic |
| Al2O3 | Amphoteric |
| SiO2 | Weakly acidic |
| P4O18 | Acidic |
| SO2 | Acidic |
| Cl2O7 | Strongly acidic |
Uses of Amphoteric Oxide
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Some of the most popular uses for amphoteric oxide salts are as follows:
Zinc Oxide
Zinc Oxide can be used as an ingredient in a variety of products and materials, including plastics, rubbers, glass, ceramics. The compound is also used in lubricants, cement, ointments, paints, sealants, adhesives, foods, pigments, fire retardants, batteries, and first-aid tapes.
Aluminium Oxide
Aluminium Oxide (Al2O3) is also utilised in the aluminium manufacturing process. Furthermore, because it is chemically white and inert, this oxide is a popular filler in plastics.
- It's a popular component in sunscreen and may also be found in cosmetics like lipstick, nail paint, and blush.
- Aluminium oxide is occasionally used as a component in a variety of glass forms.
- It can be employed as a catalyst in the Claus process and the dehydration of alcohol to alkenes.
- Aluminium oxide is also known as amphoteric oxide.
Lead Oxide
Lead Oxide (PbO) is widely used in the production of glass. Depending on the kind of glass, the benefits of employing PbO in glass may include decreased viscosity, increased refractive index, increased capacity to absorb X-rays, and increased electrical resistivity of the glass.
- Adding PbO to industrial ceramics (and glass) makes them electrically and magnetically inert (raises the Curie temperature).
- It is widely used for these purposes.
Is aluminium an Amphoteric Acid?
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At the point when the oxides of amphoteric elements begin to turn acidic, aluminium has an electronegativity of 1.5. Oxides of elements with electronegativities as low as 1.5 easily give off oxygens in water, grabbing hydrogen's water and producing hydroxide ions.
- This is frequently due to ionic bonding; hence, the connection between oxygen and the element breaks quickly in water.
- If it is more than 1.5, the element will aggressively cling to the oxygen.
- Instead, acids are produced by covalently combining with additional oxygen to form the acid anions.
- The negative charge will exist in the oxygen atoms.
- Since the de-facto ionic/covalent character of its bonds, Al2O3 is equally likely to give off or capture the oxygens.
- In contrast, in acidic circumstances, protons in the solution will protonate the oxygen in the solution, producing water and the equivalent Al salt.
- The hydroxide ions encourage the production of additional hydroxide ions from Al's oxygens.
- It will produce water and a hydrated aluminate complex.
- In this case, the reaction is far more complex than a standard acid-base reaction.
Important Topics for JEE MainAs per JEE Main 2024 Session 1, important subtopics included in the amphoteric oxides are as follows:
Some memory based important questions asked in JEE Main 2024 Session 1 include:
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Things to Remember
- Amphoteric oxides are oxides that have the properties of both acidic and basic oxides.
- It allow them to neutralize both acids and bases.
- When these oxides combine with acid, they undergo a neutralization process that produces water and salt.
- Similarly, the alkali responds to the creation of salt and water, exhibiting an acidic characteristic.
- The hydrated oxides are formed by the interaction of aqueous solutions of metal trihalides with hydroxide.
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Sample Questions
Ques: What exactly are amphiprotic molecules? (4 marks)
Ans: Amphiprotic molecules are amphoteric entities that either donate or receive a proton or H+. Water (which is self-ionizable), amino acids (which include carboxylic acid and amine groups), and proteins are examples of amphiprotic species.
For example, the hydrogen carbonate compound ion can function as an acid, as illustrated chemically below:
CO32- + H2O HCO3- + OH CO32- + H2O
or as a foundation, as in:
HCO3- + H3O+ H2CO3 + H2O H2CO3 + H2O
It should be emphasised that while all amphiprotic species are amphoteric, not all amphoteric species are amphiprotic. Zinc oxide (ZnO) is an example of a compound that lacks a hydrogen atom and so cannot contribute a proton. To receive the electron pair from OH-, the zinc oxide atom can behave as a Lewis acid.
Ques: Is HCl amphoteric? (2 marks)
Ans: The Bronsted-Lowry concept of Amphoteric substances provides a solid foundation for understanding the concepts of acid and base. Because they differ by a proton, HCl and Cl– form a conjugate acid-base pair in Example 1. In Example 2, another conjugate acid-base pair similarly produces NH4+ and NH3.
Ques: Give the oxygen-reacting element to a basic solution? (2 marks)
Ans: Oxygen is extremely reactive with alkali metals. Alkali metals get their name because when they react with water, they create either alkaline or simple metal hydroxide. Sodium generates peroxide, lithium generates oxide, while Cesium, potassium, and rubidium generate superoxide.
Ques: Give several examples of Amphoteric oxide? (4 marks)
Ans: Consider the following amphoteric oxides examples of amphoteric oxides list:
- ZnO(s) + 2NaOH(aq) → Na2ZnO2 (aq) + H2O(l)
- ZnO(s) + 2HNO3(aq) → Zn(NO3) 2(aq) + H2O(l)
- Al2O3 + 2NaOH(aq) → 2NaAlO2(aq) + H2O(l)
- Al2O3(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2O(l)
These are a few examples of amphoteric oxides. The aluminates and zincates have the ending -ate to indicate that their ions are compound ions including oxygen – similar to carbonates, nitrates, and sulphates, showing that the ions are ZnO22 and the aluminate ions are AlO2. Ions are represented by the symbols Al(OH)4 and Zn(OH)24. It should be noted that aluminate and sodium zincate are both water-soluble.
Ques: Are metal oxides said to be amphoteric oxides? (4 marks)
Ans: No. Amphoterism is defined as a distinctive manifestation of the metal's non-metallic nature, as it refers to the metal's ability to exhibit non-metallic qualities in some form. To put it another way, the amphoterism of a few oxides is most likely connected to the metal's capacity to polarise the oxide ions to which it is bound, allowing a large amount of the covalent character to be incorporated into the bond.
This is why the most common amphoteric metal oxides (as well as hydroxides) are those derived from a "borderline" metal:
- Al, - forms Al2O3 and Al(OH)3;
- Zn, - forms ZnO and Zn(OH)2;
- Be, - forms BeO and Be(OH)2;
- Sn, - forms SnO and Sn(OH)2;
- Ga, - forms Ga2O3 and Ga(OH)3.
In other words, metal oxides of metals like Group 1 and 2 metals (except for Be) do not exhibit amphoterism.
Ques: Nitrogen or Amines: which is more basic in nature? (2 marks)
Ans: The amines' fundamental existence is dependent on the donation of one nitrogen pair. The electron releasing group, such as -CH3, improves the basicity of the amine by raising electron density over nitrogen, which facilitates the donation of lone electron pairs. (CH3)2NH is the most straightforward.
Ques: What are the physical properties of amphoteric oxides? (3 marks)
Ans: The physical properties of amphoteric oxides are as follows:
- Amphoteric oxides have high boiling point and melting points.
- They are insoluble in water.
- Since they have covalent form as a result large amount of energy for dissolving.
Ques: What are the chemical properties of amphoteric oxides? (3 marks)
Ans: The chemical properties of amphoteric oxides are as follows:
Reaction with acids:
- PbO+2HCl→PbCl2+H2O
- Al2O3+6HCl→2AlCl3+3H2O
- ZnO+H2SO4→ZnSO4+H2O
Reaction with bases:
- PbO+2NaOH+H2O→Na2[Pb(OH)4]
- Al2O3+2NaOH+3H2O→2Na[Al(OH)4]
Ques: Answer the following: (A) What elements are amphoteric oxides?
(B) How many amphoteric oxides are there? (2 marks)
Ans: (A) Zinc, tin, lead, aluminium, and beryllium are different types of amphoteric oxides.
(B) There are three types of amphoteric oxides namely neutral oxides, acidic oxides, and basic oxides.
Ques: What is the use of zinc oxide? (2 marks)
Ans: Zinc Oxide (ZnO) can be used as an ingredient in a variety of products and materials, including plastics, rubbers, glass, ceramics, lubricants, cement, ointments, paints, sealants, adhesives, foods, pigments, fire retardants, batteries, and first-aid tapes.
Ques: How are hydrated oxides are formed? (2 marks)
Ans: The hydrated oxides are formed by the interaction of aqueous solutions of metal trihalides with hydroxide. Because of the increasing metallic nature of the elements involved, there is a shift from acidic oxides to amphoteric to basic as one moves down the group. Al2O3 is the formula for amphoteric oxide.
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