What is an amphoteric molecule

Amphibians in what they consist, types and examples

The Amphoteric they are the compounds or ions which, according to the theory of Bronsted and Lowry, have the property of being able to behave like acids or similar bases. The name comes from the Greek word Amphoteroiwhich means "both".

Many metals form amphoteric oxides or hydroxides, including copper, zinc, tin, lead, aluminum, and beryllium. The amphoteric property of these oxides depends on the oxidation states of the oxide in question. Examples of these substances are given at the end of the article.

Metal oxides that can react with acids and bases to create salts and water are known as amphoteric oxides. Lead and zinc oxides, among other compounds, are very good examples.

index

  • 1 What are the amphoteric?
  • 2 types of amphoteric
    • 2.1 Protonic or amphiprotic acidic substances
    • 2.2 Basic protophilic or amphiprotic substances
    • 2.3 Neutral substances
  • 3 examples of amphoteric substances
    • 3.1 Amphoteric oxides
    • 3.2 Amphoteric hydroxides
  • 4 differences between amphoteric, amphiprotic, ampholytic and aprotic
  • 5 references

What are the amphoteric?

According to Bronsted and Lowry's acid-base theory, acids are those substances that donate protons, while bases are those that accept or take in protons.

An amphoteric molecule will have reactions in which it acquires protons as it also has the ability to donate them (although this is not always the case, as will be seen in the next section).

An important and well-known case is that of the universal solvent water (H2O). This substance reacts easily with acids, e.g. when reacting with hydrochloric acid:

H2O + HCl → H3O+ + Cl-

At the same time, however, it has no problems reacting with a base, as in the case of ammonia:

H2O + NH3 → NH4 + OH-

It can be seen from these examples that water acts entirely as an amphoteric substance.

Types of amphoteric

Although amphoteric substances can be molecules or ions, there are some molecules that show amphoteric properties best and help to better study this behavior: amphiprotic substances. These are molecules that can specifically donate or accept a proton to act as an acid or base.

It should be made clear that all amphiprotic substances are amphoteric, but not all amphoteric are amphiprotic; there are amphoters that have no protons, but can behave in other ways like acids or bases (according to Lewis theory).

Amphiprotic substances include water, amino acids, and bicarbonate and sulfate ions. In turn, amphiprotic substances are also subclassified according to their ability to donate or release protons:

Acid protophenic or amphiprotic substances

They are the ones who have a greater tendency to create a proton than to assume one. Among these are sulfuric acid (H.2SO4) and acetic acid (CH3COOH), among others.

Basic protophilic or amphiprotic substances

They are the ones who are more likely to accept a proton than to give up. Among these substances one can consider ammonia (NH3) and ethylene diamide [C.2H4(NH2)2].

Neutral substances

They have the same ability or ability to accept a proton in order to surrender it. Among these are water (H.2O) and low alcohols (-ROH), mainly.

Examples of amphoteric substances

Now that the amphoteric substances have already been described, it is necessary to give the examples of reactions in which these properties are presented.

The carbonic acid ion represents a basic case of an amphiprotic substance; its reactions are shown below when it acts as an acid:

HCO3- + OH- → CO32- + H2O

The following reaction occurs when acting as a base:

HCO3- + H3O+ → H2CO3

There are many other substances as well. Of these, the following are examples:

Amphoteric oxides

As already mentioned, zinc oxide is an amphoteric but not an amphiprotic substance. Here's why.

Behave like acid:

ZnO + H2SO4 → ZnSO4 + H2O

Behavior as a basis:

ZnO + 2NaOH + H2O → Well2[Zn (OH)4]

Lead oxide (PbO), aluminum (Al2O3) and tin (SnO) also have their own amphoteric properties:

Behave as acids:

PbO + 2HCl → PbCl2 + H2O

Al2O3 + 6 HCl → 2 AlCl3 + 3H2O

SnO + HCl ↔ SnCl + H2O

And as bases:

PbO + 2NaOH + H2O → Well2[Pb (OH)]4]

Al2O3 + 2NaOH + 3H2O → 2Na [Al (OH)4]

SnO + 4NaOH + H2O ↔ Na4[Sn (OH)6]

There are also amphoteric oxides made from gallium, indium, scandium, titanium, zirconium, vanadium, chromium, iron, cobalt, copper, silver, gold, germanium, antimony, bismuth. and the tellurium.

Amphoteric hydroxides

Hydroxides can also have amphoteric properties, as in the case of aluminum hydroxide and beryllium. The following are both examples:

Aluminum hydroxide as acid:

Al (OH)3 + 3 HCl → AlCl3 + 3H2O

Aluminum hydroxide as base:

Al (OH)3 + NaOH → Na [Al (OH)4]

Beryllium hydroxide as acid:

Be (OH)2 + 2 HCl → BeCl2 + H2O

Beryllium hydroxide as base:

Be (OH)2 + 2NaOH → Na2[Be (OH)4]

Differences between amphoteric, amphiprotic, ampholytic and aprotic

Knowing how to distinguish the concept of each term is necessary as its similarity can get confusing.

It is known that amphoteric substances are substances that act like acids or bases in a reaction that creates a salt and water. They can do this by donating or capturing a proton, or simply by adopting or abandoning an electronic pair, as is Lewis' theory.

In contrast, amphiprotic substances are those amphoteric substances that act as acids or bases with the release or uptake of a proton according to Bronsted-Lowry's law. All amphiprotic substances are amphoteric, but not all amphoteric are amphiprotic.

Ampholytes are amphoteric molecules that exist as zwitterions and have dipolar ions in certain pH intervals. They are used as buffers in buffer solutions.

After all, aprotic solvents are those that have no protons and cannot absorb them.

credentials

  1. Amphoteric (2008). Wikipedia. Retrieved from en.wikipedia.org
  2. Anne Marie Helmenstine, P. (2017). What does amphoteric mean in chemistry? Retrieved from thinkco.com
  3. BICPUC. (2016). Amphoteric compounds. Retrieved from medium.com
  4. Chemicole (see). Definition of amphoteric. Retrieved from chemicool.com.