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Amphoterism

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Amphoterism Definition

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Amphoteric meaning, in the simplest term, can be stated as any compound that can be mixed with other compounds both as a base and an acid. For example, water is amphoteric. It can be transformed into a compound that can be used as an alkali or an acid. Most amphoteric compounds are metal oxides or hydroxides.  

Amphoterism is a popular term in the field of chemistry explaining the reactivity of a compound that shows alkaline nature when mixed with an acid and demonstrates acidic characteristics in an alkaline environment. 

As water is amphoteric, it is used widely for such reactions. When acid reacts with water, it gives off H3O+ ion adding an H+ ion from the acid. On the other hand, when water is combined with a base, it donates an H+ ion to the base and releases OH- ion. 

Besides water, many oxides and hydroxides are vastly utilized in amphoterism. Now that amphoteric meaning is clear enough, let us see how you can identify an amphoteric substance. 

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How to Identify an Amphoteric Substance?

While experimenting in the laboratory, how would you recognize an amphoteric compound? How to match the properties to the amphoteric definition that you have just read? Here is how you can define the amphoteric characteristics in a compound. 

  • When an amphoteric substance is mixed with an acid, it would take up hydrogen from the acid creating an H3O+ ion. 

  • When the amphoteric compound reacts to a base, it supplies hydrogen to the alkaline compound and releases an OH- ion. 

The Bronsted Lowry theory states that 'acids are proton donors and bases are proton acceptors.'. The substances that have both these characteristics are identified as amphoteric substances. 


Amphoteric Hydroxides

Hydroxides are famous for using amphoterism. Not all metals can be used as amphoteric hydroxides. Hydroxides that are made of highly charged metal cations are used for amphoterism. 

They can react in two conditions. They can either function as a Bronsted lowry base by receiving protons or work as Lewis acid by receiving a pair of electrons. 

In acidic conditions, a simple neutralization reaction occurs. As mentioned before, here the hydroxide would react as a base and would either give off protons or accept electrons. 

In an alkaline condition, the hydroxide will behave just like an acid by accepting protons from the other reactant. 


Amphoteric Hydroxide Examples or Simply, Amphoteric Examples List is Given Below.

  • Aluminium hydroxide

  • Zinc hydroxide

  • Copper hydroxide

  • Chromium hydroxide

  • Beryllium hydroxide

  • Tin hydroxide


Amphoteric Amino Acid

The carboxyl group in amino acids is responsible for their amphoteric properties. They are widely used for amphoterism. An amphoteric amino acid contains both acidic and alkaline elements like COOH and NH2

When present in an acidic condition, an amino acid would act as a base. It will carry away the positively charged ions and get attracted to the negative ions. It gives off the protons or accepts electrons.

On the other hand, while reacting with a base, it possesses acidic characteristics by carrying negative ions and accepting protons. Amino acids are excellent for amphoterism.

One example of amphoteric amino acids is glycine.


Amphoteric Oxides

Just like the hydroxides, some oxides are also amphoteric. The amphoteric characteristics depend on the oxidation state of the compound. 

When a metal oxide reacts with an acid, you can witness a neutralization reaction just like an amphoteric hydroxide. It will accept protons from the acid and produce salt. 

In contrast to this reaction, a metal oxide would produce salt and water when it reacts with an alkali. It would give off protons to the other reactant. 

Amphoteric oxides are pretty similar to amphoteric hydroxides.


Some Common Oxide Amphoteric Examples are Given Below.

  • Aluminum oxide

  • Lead oxide

  • Zinc oxide

  • Tin oxide

  • Beryllium oxide

  • Chromium oxide

  • Copper oxide


Aluminum Amphoteric

Aluminum is well-known for its amphoteric properties. All compounds made with aluminum are amphoteric compounds. All of these compounds can be used as both acids or bases.

Aluminum amphoteric can be used in many forms to let them react as acids or bases. It reacts similarly to other amphoteric compounds. It accepts protons when mixed with an acid and releases protons when it reacts to an alkali. 

Aluminum chloride, aluminum oxide, aluminum hydroxide are some examples of aluminum amphoteric. 

As you can see in the amphoteric list above, you can imagine how important it is in the field of chemistry. Amphoteric reactions are used to study the properties of elements and analyze the periodic table. 

The amphoteric examples given above have many compounds that can be applied both as an acid and an alkali. These compounds help in laboratory work as well. As one compound acts both as an acid and a base, you can observe various reactions with the same compound.


Fun Facts

Do you know that water is a neutral oxide as well as an amphoteric substance? Neutral substances hardly show any alkaline or acidic properties. But amphoteric compounds show both acidic and alkaline characteristics. Water, however, is the only compound that can be both a neutral substance and an amphoteric substance depending on the situation.

FAQ (Frequently Asked Questions)

1. How Can One Identify a Substance as an Amphoteric Substance?

Ans: An amphoteric substance reacts like an alkali when combined with an acid. In contrast, it reacts as an acid when it encounters an alkaline solution. Thus an amphoteric substance can be both an acid and a base depending on the condition they are in. To identify an amphoteric substance, you can test a compound with an alkaline and an acidic solution. If the compound accepts proton while reacting to acid and releases proton while reacting to a base, it can be stated as an amphoteric element. The best way to identify an amphoteric substance is to go for a laboratory experiment and observe the alkaline and acidic properties of the compound. If it shows both properties, then it is an amphoteric compound. 

2. What are Some Examples of Amphoteric Substances?

Ans: The most commonly used and available amphoteric substance is water. Water can act as both base and acid depending on the condition of the reaction. Besides water, many other metal oxides, metal hydroxides, and amino acids show amphoteric properties. Another popular amphoteric element is aluminum. Aluminum oxides and hydroxides are amphoteric. Amino acid, like Glycine, also shows amphoteric characteristics. Many other elements like zinc, copper, beryllium, tin, lead, titanium, chromium, scandium, indium, and many more elements can be transformed into compounds to use as amphoteric compounds.  Most amphoteric compounds are either oxides and hydroxides.