Equilibrium: Acids, Bases, and Buffers

Comprehensive vocabulary flashcards covering chemical equilibria, acid-base theories, pH, pKa, dissociation constants, and biological buffer systems.

Equilibrium Constant ($K_c$)

A numerical value describing the relationship between reactant and product concentrations at dynamic equilibrium, calculated using $K_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}$, where stoichiometric coefficients serve as power exponents.

Ionic Product of Water ($K_w$)

The equilibrium constant for the self-ionization of water, given by $K_w = [H_3O^+][OH^-]$, which equals $1.0 \times 10^{-14}$ at $25\,^\circ\text{C}$ ($298\,\text{K}$).

Arrhenius Acid

A substance that dissociates in aqueous solution to produce hydrogen ions ($H^+$), reacting with water molecules to increase the concentration of hydronium ions ($H_3O^+$).

Arrhenius Base

A substance that dissociates in aqueous solution to produce hydroxide ions ($OH^-$), increasing the hydroxide ion concentration in water.

Brønsted-Lowry Acid

A molecule or ion that acts as a proton ($H^+$) donor in an acid-base reaction.

Brønsted-Lowry Base

A molecule or ion that acts as a proton ($H^+$) acceptor in an acid-base reaction.

Conjugate Acid-Base Pair

Two chemical substances related in a reaction that differ from one another by exactly one single proton ($H^+$) and a single ionic unit of charge.

Polyprotic Acid

An acid capable of donating two or more protons during successive ionization reactions (e.g., sulfuric acid, $H_2SO_4$, and carbonic acid, $H_2CO_3$).

Amphoteric Substance

A chemical substance that can either donate or accept protons depending on conditions, enabling it to act as either an acid or a base (e.g., $H_2O$ and $HSO_4^-$).

Zwitterion

A dipolar molecule containing both a distinct positive and negative electrical charge simultaneously while maintaining zero net electrical charge, typical of amino acids in neutral solutions.

pH

A logarithmic measure of hydronium ion concentration defined by the inverse base-10 logarithm equation: $\text{pH} = -\log_{10}[H_3O^+]$.

pOH

A logarithmic measure of hydroxide ion concentration defined by the inverse base-10 logarithm equation: $\text{pOH} = -\log_{10}[OH^-]$.

Strong Acid

An acid that completely ($100\%$) ionizes and dissociates in aqueous solution into protons and conjugate base anions (e.g., $HCl$, $HNO_3$, $H_2SO_4$).

Weak Acid

An acid that ionizes only partially in water, establishing a dynamic chemical equilibrium between the intact undissociated acid and its dissociated conjugate base and hydronium ions.

Strong Base

A base that dissociates completely into metal cations and hydroxide ions in aqueous solution, including $LiOH$, $NaOH$, $KOH$, $RbOH$, and $CsOH$.

Acid Dissociation Constant ($K_a$)

The equilibrium constant for the dissociation of a weak acid, calculated via the ratio $K_a = \frac{[A^-][H_3O^+]}{[HA]}$, quantifying acid strength by the extent of ionization.

Base Dissociation Constant ($K_b$)

The equilibrium constant for the ionization of a weak base in water, calculated via the ratio $K_b = \frac{[BH^+][OH^-]}{[B]}$.

Henderson-Hasselbalch Equation

An equation relating pH, $pK_a$, and the ratio of dissociated to undissociated forms of an acid: $\text{pH} = pK_a + \log_{10}\left(\frac{[A^-]}{[HA]}\right)$.

Buffer Solution

A solution containing balanced concentrations of a weak acid and its conjugate base (or a weak base and its conjugate acid) that resists significant changes in pH when small amounts of acid or base are added.

Major Biological Buffer Systems

Physiological buffer mechanisms maintaining stable internal fluid pH, including the bicarbonate buffer system in blood and the phosphate buffer system in intracellular fluid and urine.

pH Meter

An electrochemical laboratory apparatus that measures voltage differences generated by hydrogen ion concentrations across a reference electrode and a measurement electrode submerged in solution.