Acids, Bases, and pH

Water Ionization

• Covalent bonds in water can spontaneously break, leading to ionization.

• Water molecule loses a hydrogen atom, resulting in a hydroxide ion.

• Measuring Water Ionization

• [H^+] in pure water is 1 \times 10^{-7} M.

• [OH^-] in pure water is also 1 \times 10^{-7} M.

• [H^+] \times [OH^-] = 1 \times 10^{-14} M^2.

• Hydronium ions are represented as H^+.

Acids

• Acids are H^+ donors, increasing [H^+] and decreasing pH [OH^-] in solutions.

Bases

• Bases are H^+ acceptors, decreasing [H^+] in solutions, often by releasing OH^- ions (increasing pH [OH^-]).

• Not all bases directly release OH^- but all accept H^+ ions.

Acids vs. Bases

• Acidic solution: More H^+, less OH^-.

• Basic solution: Less H^+, more OH^-.

• Neutral solution: H^+ = OH^-.

pH

• pH measures the concentration of H^+ in a solution on a logarithmic scale.

• pH = -log[H^+].

• In pure water at equilibrium: [H^+] = 1 \times 10^{-7} M, [OH^-] = 1 \times 10^{-7} M, pH = 7.

• [H^+] and [OH^-] always equals 1 \times 10^{-14} M.

Buffers

• Buffers minimize pH changes by absorbing or releasing H^+ ions.

• Accept H^+ when pH is too low (acidic).

• Donate H^+ when pH is too high (basic).

• Buffers are combinations of weak acid and its conjugate base (or vice versa).

Buffer Chemical Behavior

• Add acid: Buffer accepts added H^+.

• Add base: Buffer gives up H^+.