Question

When is a molecular compound named as an acid?

Short answer

A molecular compound is named as an acid when it contains hydrogen atoms in its chemical formula, exhibits characteristic acid properties, and follows the IUPAC acid naming conventions. Examples include hydrochloric acid (HCl), sulfuric acid (H2SO4), and nitric acid (HNO3). Acids can be identified by their reactions with metals, carbonates and bicarbonates, sour taste, and pH values less than 7. Binary acids are named as "hydro-ic acid," while oxyacids are named based on the polyatomic anion they contain, with "ic acid" for -ate anions and "ous acid" for -ite anions.

Step-by-step solution

Identifying Acids by Chemical Formula

The simplest way to identify whether a molecular compound is an acid is to observe the chemical formula. Acids have hydrogen atoms in their formula, typically present at the beginning of the formula. For example, hydrochloric acid (HCl), sulfuric acid (H2SO4), and nitric acid (HNO3) are all acids that contain hydrogen atoms in their formulas.

Identifying Acids by their Chemical Properties

Acids can also be identified by their characteristic properties. These include: 1. Acids react with metals to produce hydrogen gas. 2. Acids react with carbonates and bicarbonates to form carbon dioxide gas. 3. Acids taste sour. 4. Acids have a pH value less than 7. For example, hydrochloric acid (HCl) reacts with zinc to produce hydrogen gas, and sulfuric acid (H2SO4) reacts with sodium bicarbonate to produce carbon dioxide gas.

Identifying Binary Acids by their IUPAC Naming

Binary acids consist of hydrogen and one other nonmetal element. These acids are named as "hydro-ic acid" based on the nonmetal element present in the compound according to the IUPAC (International Union of Pure and Applied Chemistry) naming system. Examples include: 1. HCl: Hydrochloric acid 2. HF: Hydrofluoric acid 3. HI: Hydroiodic acid

Identifying Oxyacids and Their IUPAC Naming

Oxyacids are compounds containing hydrogen, oxygen, and another nonmetal element in their composition. In the IUPAC naming system, oxyacids are named based on the polyatomic anion they contain. 1. If the anion ends in -ate, the oxyacid is named as "ic acid." Example: H2SO4, containing sulfate (SO4^2-), is called sulfuric acid. 2. If the anion ends in -ite, the oxyacid is named as "ous acid." Example: H2SO3, containing sulfite (SO3^2-), is called sulfurous acid. A molecular compound is named as an acid when it meets the criteria mentioned above, such as having hydrogen atoms in its chemical formula, demonstrating classical acid properties, and following the IUPAC acid naming conventions.

Key concepts

Chemical Formula Identification

In chemistry, identifying chemical compounds by their formulas is an essential skill. For acids, they generally have hydrogen atoms, often denoted as the first element in their chemical formula.
Hydrogen is a key marker because acids release hydrogen ions ( H^+ ) when dissolved in water. This property is what gives acids their characteristic behaviors. For instance:

• HCl stands for hydrochloric acid.
• HNO3 is nitric acid.
• H2SO4 indicates sulfuric acid.

These formulas show hydrogen in the lead position, hinting that they are indeed acids. Recognizing these patterns is the first step in acid identification.

Chemical Properties of Acids

Understanding the properties of acids helps in further identification and categorization of these compounds. Acids exhibit several distinct properties:

• They are known for their sour taste. Think of vinegar's tartness, which is acetic acid.
• Acids can react with metals, producing hydrogen gas. This is why acids are often stored in non-metal containers.
• They react vigorously with carbonates to release carbon dioxide gas.
• The pH scale, which measures acidity, shows that acids have a pH less than 7.

By observing these traits, one can reliably identify a compound as an acid in the lab or in everyday applications.

IUPAC Naming Rules

The International Union of Pure and Applied Chemistry (IUPAC) has set systematic naming rules to provide clarity and consistency across chemical nomenclatures. This is crucial for proper communication among scientists worldwide.
For acids, the naming depends on their composition:

• If the formula consists only of hydrogen and a nonmetal, it's a binary acid, typically named as "hydro-ic acid."
• If the compound involves hydrogen, oxygen, and another element (an oxyacid), it reflects the anion's name, like "ic acid" for those with an -ate anion and "ous acid" for ones with an -ite anion.

These guidelines aid in identifying and naming acids correctly, ensuring everyone speaks the same 'chemical language.'

Binary Acids

Binary acids are a special type of acid composed of hydrogen and a single nonmetal element. They do not contain oxygen, which makes them different from oxyacids.
In their naming, the nonmetal component determines the name, following the "hydro-ic acid" format. Examples include:

• HCl, known as hydrochloric acid.
• HF, called hydrofluoric acid.
• HI, referred to as hydroiodic acid.

Understanding the structure and naming of binary acids is crucial in distinguishing them from other acidic types. Their simple composition allows for straightforward identification.

Oxyacids

Oxyacids are acids that include hydrogen, oxygen, and another nonmetal element. This additional complexity necessitates a slightly different naming approach compared to binary acids.
The name of an oxyacid depends on the polyatomic ion (the anion part of the acid):

• If the anion name ends in -ate, the acid name ends in -ic. For example, H2SO4, with sulfate ( SO4^{2-} ), is sulfuric acid.
• If the anion name ends in -ite, the acid name ends in -ous. For instance, H2SO3, which contains sulfite ( SO3^{2-} ), is called sulfurous acid.

Comprehending how oxyacids are named helps in analyzing their chemical behaviors and applications.