Nomenclature of Acidic Compounds

Introduction

Acids are chemical compounds that donate protons (H⁺ ions). They are classified as either monoprotic (donating one proton), diprotic (donating two protons), or polyprotic (donating more than two protons). The nomenclature of acidic compounds follows specific rules depending on the acid's composition and anion.

Binary Acids

Binary acids contain only two elements: hydrogen and a nonmetal. Their names begin with the prefix "hydro-" followed by the stem of the nonmetal's name, and end with the suffix "-ic acid". For example, HCl is hydrochloric acid, and HBr is hydrobromic acid.

Oxoacids

Oxoacids contain hydrogen, oxygen, and a nonmetal. Their nomenclature is based on the oxidation state of the central nonmetal atom. The rules are more complex and involve different suffixes and prefixes:

-ite suffix: indicates a lower oxidation state of the central nonmetal. Example: H₂SO₃ is sulfurous acid.
-ate suffix: indicates a higher oxidation state of the central nonmetal. Example: H₂SO₄ is sulfuric acid.
Prefixes (hypo- and per-): These prefixes are used for oxoacids with even lower or higher oxidation states, respectively. Example: HClO is hypochlorous acid, and HClO₄ is perchloric acid.

Examples

Acid Formula	Acid Name
HCl	Hydrochloric acid
HBr	Hydrobromic acid
H₂SO₄	Sulfuric acid
H₂SO₃	Sulfurous acid
HNO₃	Nitric acid
HNO₂	Nitrous acid
H₃PO₄	Phosphoric acid

Acidity and pKa

The acidity of an acid is determined by its dissociation constant (K_a). The pK_a (=-log K_a) value is a measure of acid strength; a lower pK_a indicates a stronger acid.

Conclusion

Understanding the nomenclature of acidic compounds is crucial for effective communication and understanding of chemical reactions. The system allows for unambiguous naming of acids based on their composition and structure.

Nomenclature of Acidic Compounds

Acids are chemical compounds that can donate protons (H⁺ ions). They are named according to the following rules:

Binary acids, which contain hydrogen and only one other nonmetal element, are named using the prefix "hydro-" followed by the root name of the other element and the suffix "-ic acid". For example, HCl is hydrochloric acid and HBr is hydrobromic acid.
Oxyacids, which contain hydrogen, oxygen, and another nonmetal element, are named based on the oxidation state of the central nonmetal atom. The suffix "-ic acid" is used when the central atom is in its higher oxidation state, and the suffix "-ous acid" is used when it is in a lower oxidation state. For example:
- HNO₃ is nitric acid (nitrogen in +5 oxidation state)
- HNO₂ is nitrous acid (nitrogen in +3 oxidation state)
- H₂SO₄ is sulfuric acid (sulfur in +6 oxidation state)
- H₂SO₃ is sulfurous acid (sulfur in +4 oxidation state)
Polyprotic acids, which can donate more than one proton, are named similarly to other acids. The prefix "di-", "tri-", etc., is not typically used in the name itself to indicate the number of acidic hydrogens, although it might be used in descriptions (e.g., "diprotic acid"). For example:
- H₂SO₄ is sulfuric acid (diprotic)
- H₃PO₄ is phosphoric acid (triprotic)

The strength of an acid is determined by its ability to donate protons. Strong acids donate protons easily and completely in aqueous solution, while weak acids donate protons less readily and incompletely. The strength of an acid is quantitatively expressed by its acid dissociation constant (K_a) or its negative logarithm, the pK_a value. The lower the pK_a value, the stronger the acid.

Experiment: Nomenclature of Acidic Compounds

Materials:

Various aqueous solutions of acids (e.g., hydrochloric acid (HCl), sulfuric acid (H₂SO₄), nitric acid (HNO₃), acetic acid (CH₃COOH), phosphoric acid (H₃PO₄))
pH paper
Universal indicator solution
Buret
Volumetric flask
Sodium hydroxide (NaOH) solution of known concentration
Pipettes
Beaker

Procedure:

Obtain aqueous solutions of several acids. Note the name and formula of each acid.
Use pH paper to determine the approximate pH of each solution. Record the pH for each acid.
Using a volumetric flask and pipette, prepare a precisely measured volume (e.g., 25 mL or 50 mL) of each acid solution.
Using a buret, titrate a precisely measured volume of each acid solution with a known concentration of sodium hydroxide (NaOH) solution until the endpoint is reached (e.g., using universal indicator or pH meter). Record the volume of NaOH used for each titration.
Calculate the concentration of each acid using the titration data and stoichiometry.
Compare the calculated concentrations with the expected values (if available).

Key Procedures:

Determination of pH: pH paper is used to approximate the pH of each acid solution. The color change of the paper, compared to a color chart, indicates the approximate pH. More precise pH measurements can be obtained using a pH meter.

Titration: Titration involves the careful addition of a known concentration of base (NaOH) to a known volume of acid until the equivalence point is reached, indicated by a color change of an indicator or a sharp change in pH (using a pH meter). This allows for the calculation of the unknown acid concentration.

Significance:

This experiment demonstrates the nomenclature of acidic compounds by allowing students to work directly with several common acids. It also reinforces their understanding of acid-base chemistry and analytical techniques. By performing titrations, students can:

Classify acids based on their strength (strong or weak) based on their pH and titration behavior.
Determine the concentration of unknown acid solutions using stoichiometric calculations.
Practice using common laboratory equipment and techniques (e.g., buret, volumetric flask, pipette, pH paper).
Enhance their understanding of acid-base reactions and chemical equilibrium.

The experiment also allows for the application of nomenclature rules to correctly name the acids used.

Related Topics

Nomenclature of Acidic Compounds