DRUG DELIVER 1 CHP. 4 Ionic Equilibria and Buffers

Vocabulary flashcards covering electrolytes, acids/bases/salts, ionization, buffer systems, Henderson–Hasselbalch, pH calculations, and related concepts.

Electrolyte

A substance (acid, base, or salt) that ionizes in water to yield cations and anions.

Strong electrolyte

A substance that completely ionizes in water, producing a high concentration of ions (e.g., HCl, NaCl).

Weak electrolyte

A substance that only partially ionizes in water (e.g., atropine, phenobarbital, sulfadiazine).

Nonelectrolyte

A substance that does not ionize in water and does not conduct electricity (e.g., sucrose, urea, glycerol).

Cation

A positively charged ion.

Anion

A negatively charged ion.

Acid

A substance that donates a proton (H+) to a base; increases H3O+ in solution.

Base

A substance that accepts a proton; increases OH− in solution.

Salt

A compound formed from an acid and a base; in water, ions may hydrolyze (e.g., NaCl).

Hydrolysis

Reaction of ions with water that can change the solution's pH by producing H+ or OH−.

Salts hydrolysis categories

Classifications: salts of strong acids/strong bases; salts of weak acids/strong bases; salts of strong acids/weak bases; salts of weak acids/weak bases.

Ka

Acid dissociation constant; Ka = [H+][A−]/[HA], measures acid strength.

Kb

Base dissociation constant; Kb = [BH+][OH−]/[BOH], measures base strength.

pKa

Negative logarithm of Ka; pKa = −log10(Ka).

pKb

Negative logarithm of Kb; pKb = −log10(Kb).

pH

Negative logarithm of hydronium ion concentration; measures acidity.

pOH

Negative logarithm of hydroxide ion concentration.

Buffer

A solution containing a weak acid and its conjugate base (or a weak base and its conjugate acid) that resists pH changes.

Buffer capacity

A measure of how much strong acid or base a buffer can absorb before a given pH change occurs.

Henderson–Hasselbalch equation

Relates pH to the buffer components: pH = pKa + log([base]/[acid]) for weak acid buffers (and equivalently pH = pKa + log([A−]/[HA]).

Diprotic acid

An acid that donates two protons per molecule (H2A) and has two dissociation constants Ka1 and Ka2.

Ampholyte

A substance that can act as either an acid or a base depending on the pH (amphoteric).

Amphoteric

Describes a substance capable of behaving as both an acid and a base.

pH partition hypothesis

Absorption of a weak electrolyte depends on the fraction in the unionized form at the absorption site; unionized forms are more lipid-soluble.

Ionization percentage

The percent of a weak electrolyte that exists in ionized form at a given pH.

Ionic strength

A measure of the total concentration of ions in solution, affecting ionization and activity.

pKw

Ion-product of water; at 25°C, pKw = 14.