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: (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:

• Example: Acid: HCl Base: H2O Conjugate Acid: H3O+ Conjugate Base: Cl-

• Another Example:

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:

• 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:

• 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.