AMPHOTERIC: WHAT THEY CONSIST OF, TYPES AND EXAMPLES - CHEMISTRY - 2024

The amphoteric are compounds or ions having the particularity of being able to act as an acid or base, according to the theory Bronsted Lowry. Its name comes from the Greek word amphoteroi, which means "both."

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

Amphoteric surfactant

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

What are amphoteric?

According to the acid-base theory of Bronsted and Lowry, acids are those substances that donate protons, while bases are those that accept or take up protons.

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

An important and well recognized case is that of the universal solvent, water (H2O). This substance reacts easily with acids, for example, in reaction with hydrochloric acid:

H ₂ O + HCl → H ₃ O ⁺ + Cl ^-

But at the same time, it also has no problem reacting with a base, as in the case of ammonia:

H ₂ O + NH ₃ → NH ₄ + OH ^-

With these examples it can be seen that water fully acts as an amphoteric substance.

Types of amphoteric

Even though amphoteric substances can be molecules or ions, there are some molecules that better demonstrate amphoteric characteristics 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 clarified that all amphiprotic substances are amphoteric, but not all amphoteric substances are amphiprotic; there are amphoteric that do not possess protons but can behave like acids or bases in other ways (as per 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 give protons:

Acidic protogenic or amphiprotic substances

They are those that have a greater tendency to give up a proton than to accept one. Among these are sulfuric acid (H ₂ SO ₄) and acetic acid (CH ₃ COOH), among others.

Basic protophilic or amphiprotic substances

They are those for which accepting a proton is more common than giving it up. Among these substances you can find ammonia (NH ₃) and ethylenediamide.

Neutral substances

They have the same facility or capacity to accept a proton as to give it up. Among these are water (H ₂ O) and minor alcohols (-ROH), mainly.

Amphoteric character of quinolones

Examples of amphoteric substances

Now, since amphoteric substances have already been described, it is necessary to denote the examples of reactions in which these characteristics occur.

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

HCO ₃ ^- + OH ^- → CO ₃ ^2- + H ₂ O

The following reaction occurs when it acts as a base:

HCO ₃ ^- + H ₃ O ⁺ → H ₂ CO ₃

There are also many other substances. Of these there are the following examples:

Amphoteric oxides

Zinc oxide, as already mentioned, is an amphoteric but not an amphiprotic substance. The following shows why.

Behaving like acid:

ZnO + H ₂ SO ₄ → ZnSO ₄ + H ₂ O

Behaving as a base:

ZnO + 2NaOH + H ₂ O → Na ₂

Lead oxide (PbO), aluminum (Al ₂ O ₃) and tin (SnO) also have their own amphoteric characteristics:

Behaving like acids:

PbO + 2HCl → PbCl ₂ + H ₂ O

Al ₂ O ₃ + 6HCl → 2AlCl ₃ + 3H ₂ O

SnO + HCl ↔ SnCl + H ₂ O

And as bases:

PbO + 2NaOH + H ₂ O → Na ₂

Al ₂ O ₃ + 2NaOH + 3H ₂ O → 2Na

SnO + 4NaOH + H ₂ O ↔ Na ₄

Amphoteric oxides also exist from gallium, indium, scandium, titanium, zirconium, vanadium, chromium, iron, cobalt, copper, silver, gold, germanium, antimony, bismuth and tellurium.

Amphoteric hydroxides

Hydroxides can also have amphoteric characteristics, as in the cases of aluminum and beryllium hydroxide. Below are both examples:

Aluminum hydroxide as acid:

Al (OH) ₃ + 3HCl → AlCl ₃ + 3H ₂ O

Aluminum hydroxide as a base:

Al (OH) ₃ + NaOH → Na

Beryllium hydroxide as acid:

Be (OH) ₂ + 2HCl → BeCl ₂ + H ₂ O

Beryllium hydroxide as a base:

Be (OH) ₂ + 2NaOH → Na ₂

Differences between amphoteric, amphiprotic, ampholytic and aprotic

It is necessary to know how to differentiate the concept of each term, since their resemblance can become confusing.

Amphoters are known to be substances that behave like acids or bases in a reaction that produces a salt and water. They can do this by donating or capturing a proton, or simply by accepting an electronic pair (or giving it away) according to Lewis's theory.

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

Ampholyte compounds are amphoteric molecules that exist as zwitterions and possess zwitterions in certain pH ranges. They are used as buffering agents in buffer solutions.

Finally, aprotic solvents are those that do not have protons to give up and cannot accept them either.

References

1. Amphoteric. (2008). Wikipedia. Retrieved from en.wikipedia.org
2. Anne Marie Helmenstine, P. (2017). What Does Amphoteric Mean in Chemistry ?. Retrieved from thoughtco.com
3. BICPUC. (2016). Amphoteric Compounds. Retrieved from medium.com
4. Chemicool. (sf). Definition of amphoteric. Obtained from chemicool.com.