Weak acid: Encyclopedia - Weak acid

Weak acid

Acid-base reaction theories
pH
Self-ionization of water
Buffer solutions
Systematic naming
Redox reactions
Electrochemistry
Acids:

• Strong acids
• Weak acids

Bases:

• Strong bases
• Weak bases

A weak acid is an acid that does not fully ionize in solution; that is, if the acid was represented by the general formula HA, then in aqueous solution a significant amount of undissolved HA still remains.

HA_(aq) H⁺_(aq) + A^-_(aq)

The equilibrium concentrations of reactants and products are related by the Acidity constant expression, (K_a): K_a = [H⁺][A^-]/[HA].

The greater the value of K_a, the more the formation of H⁺ is favored, and the lower the pH of the solution. The K_a of weak acids varies between 1×10^-14 and 1. Acids with a K_a less then 1×10^-14 are known as garbage or worthless bases and do not exhibit any acidic properites (in this case, water is a stronger acid). Acids with a K_a of greater than 1 are strong acids and totally dissociate.

The vast majority of acids are weak acids.

Weak acid - Examples

• Phosphoric acid, H₃PO₄
• Acetic acid, CH₃COOH
• Hydrofluoric acid, HF
• Acetylsalicylic acid, C₆H₄OCOCH₃CO₂H
• Nicotinic acid, C₅H₅NCOOH
• Pyruvic acid, CH₃COCOOH
• Bromothymol blue, C₂₁H₁₅NaBr₂O₃S

Category: Acids

Adapted from the Wikipedia article "Weak acid", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki