Acids, Bases, and Neutralization: Key Concepts in General Chemistry

Acids and Bases

Definition and Etymology

The term acid is derived from the Latin word "acidus," meaning sour. Acids and bases are fundamental chemical species that participate in a wide range of chemical reactions, especially in aqueous solutions.

• General Behavior: Acids release hydrogen ions (H+) in solution, while bases release hydroxide ions (OH-).

• Example: $\mathrm{HCl} \rightarrow \mathrm{H^+} + \mathrm{Cl^-}$ (acid dissociation)

Models of Acids and Bases

• Arrhenius Model:

  • Acid: Donates H+ ions in water.

  • Base: Donates OH- ions in water.

• Brønsted-Lowry Model:

  • Acid: Donates H+ ions (proton donor).

  • Base: Accepts H+ ions (proton acceptor).

Brønsted-Lowry Theory: Conjugate Pairs

Conjugate Acid-Base Pairs

When an acid donates a proton, it forms its conjugate base. When a base accepts a proton, it forms its conjugate acid.

• General Reaction: $\mathrm{HA} + \mathrm{B} \rightleftharpoons \mathrm{A^-} + \mathrm{BH^+}$

• Example: $\mathrm{HCl} + \mathrm{H_2O} \rightarrow \mathrm{H_3O^+} + \mathrm{Cl^-}$ Acid: HCl Base: H2O Conjugate Acid: H3O+ Conjugate Base: Cl-

• Another Example: $\mathrm{HNO_3} + \mathrm{H_2O} \rightarrow \mathrm{NO_3^-} + \mathrm{H_3O^+}$

Acid Strength

Strong vs. Weak Acids

Acid strength is determined by the degree of dissociation in water. Strong acids dissociate completely, while weak acids do not.

• Six Common Strong Acids (100% dissociation):

  • HCl

  • HBr

  • HI

  • HNO3

  • HClO4

  • H2SO4

• Weak Acids: All other acids that do not dissociate completely in water.

Neutralization

Neutralization Reactions

When an acid and a base react, they neutralize each other, forming water and a salt. This is the basis for titration reactions in analytical chemistry.

• General Reaction: $\mathrm{HCl} + \mathrm{NaOH} \rightarrow \mathrm{NaCl} + \mathrm{H_2O}$

• Products: Salt (NaCl) and water (H2O)

Applications

• Titration: Neutralization reactions are used to determine the concentration of an unknown acid or base.

Special Cases

Ammonia and Water

• Ammonia (NH3): A weak base that reacts with water:

• $\mathrm{NH_3} + \mathrm{H_2O} \rightleftharpoons \mathrm{NH_4^+} + \mathrm{OH^-}$

• Water (H2O): Amphoteric, meaning it can act as either an acid or a base depending on the reaction partner.

Additional info: Amphoterism is a property of substances that can both donate and accept protons, such as water.