Classification of acids. Acid classification criteria

Acids are closely related to people's daily lives, whether in the professional or personal field. Its general characteristics are sour taste, liquid state and water ionization. These aspects are closely related to the classification of these substances, so it is very important to know it.

Classification of acids involves a wide range of criteria. Are they:

• Volatility;

• Stability;

• Degree of oxygenation;

• Hydration degree;

• Number of ionizable hydrogens;

• Strength.

a) Volatility

Volatility is the term used to say that a certain liquid material is easily transferred to the gaseous state because it has a low boiling point. In relation to this criterion, acids are classified as follows:

• volatiles: acids with a low boiling point that easily change to a gaseous state.
  Examples: HCl, HBr and HClO₄.

• Fixed: acids with high boiling points which, therefore, do not easily pass into the gaseous state.
  Examples: H₃DUST₄, H₂ONLY₄ and H₃BO₃.

b) Stability

The term stability refers to the ability of a substance not to decompose, that is, not to spontaneously transform into other substances. In relation to this criterion, acids are classified as follows:

• stable: acids that do not decompose under ambient conditions.
  Examples: HCl, HIO₄, H₂ONLY₄,...

• Unstable: acids that decompose under ambient conditions.
  Examples: H₂CO₃, H₂s₂O₃ and H₂ONLY₃.

c) Degree of oxygenation

This criterion involves the presence or absence of oxygen in the composition of acids. Therefore, acids can be classified into:

• Hidracids: acids that do not have oxygen in their composition. Examples: HI, HCN and H₂S.

• oxyacids: acids that have oxygen in their composition. Examples: H₃DUST₃, H₂ONLY₃ and HBrO₂.

d) Degree of hydration

Indicates the removal of water molecules from the formula of an acid so that it originates a new oxyacid. According to this criterion, acids can be classified into:

• meta acid: it has the lowest degree of hydration that an acid can have. It originates from the loss of a water molecule by an acid ortho.
  Example: HPO₃. the HPO₃ is a meta acid in that the ortho H acid₃DUST₄, when losing a water molecule (H₂O) becomes the goal.

• Pyro acid: it has an amount of water greater than that of the meta and less than that of the ortho. It originates when we multiply an ortho acid by 2 and then take a molecule out of water.
  Example: H₄P₂O₇. the H₄P₂O₇ is a pyro acid because when we multiply its ortho (H₃DUST₄) for two, we have the H molecule₆P₂O₈ . When removing the water molecule, we have the H₄P₂O₇.

• ortho acid: it has the highest degree of hydration that an acid can have. It is always a common acid that has a sufficient number of hydrogens and oxygens to allow the removal of a water molecule.
  Example: H₃DUST₄.

e) Number of ionizable hydrogens

According to the amount of hydrogens that can undergo ionization when added to water, acids can be classified as follows:

• monoacid: features an ionizable hydrogen. Example: HI.

• diacid: features two ionizable hydrogens. Example: H₂ONLY₃.

• Triacid: features three ionizable hydrogens. Example: H₃BO₃.

• tetracid: features four ionizable hydrogens. Example: H₄P₂O₇.

f) Strength

The strength of an acid is related to its ability to ionize a lot, a little or a fair amount. Regarding these criteria, acids are classified into:

• strong: acids that ionize a lot. Examples: H₄P₂O₇, H₂ONLY₄, HCl and HBr.

• moderateorsemi-strong: acids that ionize reasonably, that is, more than a weak and less than a strong. Examples: H₂ONLY₃, H₂s₂O₃ and HF.

• weak: acids that are poorly ionized. Examples: HClO, H₃BO₃, HCN and H₂S.

By Me. Diogo Lopes Dias

Source: Brazil School - https://brasilescola.uol.com.br/quimica/classificacao-dos-acidos.htm