Acids and Bases: Definitions, Classification, and Nomenclature

Acids and Bases: Definitions and Behavior

Introduction to Acids and Bases

Acids and bases are fundamental classes of compounds in chemistry, each with distinct properties and behaviors. Understanding their definitions, how to identify them, and how to name and write their formulas is essential for introductory chemistry students.

• Acids are compounds that have a loosely held hydrogen atom that can be donated to another compound in the form of a proton (H+). Thus, acids are proton donors.

• Bases are compounds that accept this incoming proton; they are proton acceptors.

Example: The hydrogen ion (H+) is formed when a hydrogen atom loses its single electron, leaving only a proton.

Acid-Base Reactions

A typical acid-base reaction is called a neutralization reaction, where an acid reacts with a base to produce a salt and water.

• General Equation:

$\mathrm{HCl} + \mathrm{OH}^- \rightarrow \mathrm{Cl}^- + \mathrm{H_2O}$

• Here, hydrochloric acid (HCl) donates a proton to hydroxide ion (OH-), forming chloride ion (Cl-) and water (H2O).

Typical Acids: Most acids have formulas that begin with "H" (e.g., HCl, HF, HNO3, H2SO4).

Classification of Acids

Binary (Mineral) Acids

Binary acids, also known as mineral acids, contain hydrogen and one other element.

• Examples: HCl (hydrochloric acid), HBr (hydrobromic acid), H2S (hydrosulfuric acid)

Oxyacids

Oxyacids contain hydrogen, oxygen, and at least one other element (usually a nonmetal).

• Examples: H2SO4 (sulfuric acid), HNO3 (nitric acid), H3PO4 (phosphoric acid)

Naming Acids

Naming Binary (Mineral) Acids

To name a binary acid:

1. Identify the name of the monoatomic anion the acid contains.

2. Remove the -ide suffix in the anion name and replace it with -ic.

3. Attach the prefix hydro-.

4. Pair this name with the word "acid".

Examples:

• HCl: hydrochloric acid

• HBr: hydrobromic acid

• H2S: hydrosulfuric acid

Naming Oxyacids

To name an oxyacid:

1. Do not include the prefix hydro- in the acid name.

2. Identify the polyatomic anion (oxyanion) the acid contains.

3. If the oxyanion name ends in -ate, replace this suffix with -ic.

4. If the oxyanion name ends in -ite, replace this suffix with -ous.

5. Add the word "acid" to the name.

Examples:

• H2SO4: sulfuric acid (from sulfate)

• HNO2: nitrous acid (from nitrite)

• H3PO4: phosphoric acid (from phosphate)

• HClO: hypochlorous acid (from hypochlorite)

Writing Formulas for Acids

Formulas for Binary (Mineral) Acids

When given the name of a binary acid:

1. Recognize the hydro- prefix, indicating a monoatomic anion.

2. Determine the monoatomic ion from the rest of the name.

3. Write out the formulas for a proton (H+) and the monoatomic anion.

4. Balance the charges to write the correct formula.

Examples:

• Hydroiodic acid: H+ + I- → HI

• Hydrofluoric acid: H+ + F- → HF

• Hydroselenic acid: 2H+ + Se2- → H2Se

Formulas for Oxyacids

When given the name of an oxyacid:

1. Examine the name before the word "acid".

2. If the name ends in -ic, the oxyanion name ends in -ate.

3. If the name ends in -ous, the oxyanion name ends in -ite.

4. Write down the formula for a proton and the oxyanion formula.

5. Balance the charges to write the correct formula.

Examples:

• Nitric acid: H+ + NO3- → HNO3

• Phosphorous acid: 3H+ + PO33- → H3PO3

• Perchloric acid: H+ + ClO4- → HClO4

Summary Table: Naming and Writing Formulas for Acids

Type of Acid	Naming Rule	Example Name	Formula
Binary (Mineral) Acid	hydro- + [anion root] + -ic acid	Hydrochloric acid	HCl
Oxyacid (anion ends in -ate)	[anion root] + -ic acid	Sulfuric acid	H2SO4
Oxyacid (anion ends in -ite)	[anion root] + -ous acid	Nitrous acid	HNO2

Review Questions

• Write the formula for each of the following acids: nitric acid, chloric acid, acetic acid, hydroiodic acid, sulfurous acid, dichlorous acid, phosphoric acid, nitrous acid, hydrochloric acid, perchloric acid, hydrobromic acid, carbonic acid, sulfuric acid.

• Name each of the following acids: HNO3, HF, H2SO3, HNO2, H3PO4, H2CO3, HCl, HBr, H2SO4, HClO4, H2Se, H3PO3, HClO, HI, H2S.

Additional info: The above review questions are typical practice for mastering acid nomenclature and formula writing in introductory chemistry.