Acid-Base Theory Lecture Flashcards

Flashcards covering acid-base theories, physiological pH, functional group classification, dissociation constants, and clinical applications like ion trapping and salt formation.

Homeostasis

The processes by which the body maintains a stable internal environment, such as keeping fluid pH within a narrow range for proper organ and cell function.

Normal blood pH

The vital range for human blood, defined as being between $7.35$ and $7.45$, with a typical average of $7.4$.

Small-molecule drug distribution

Approximately $60-70\%$ of marketed drugs are weak bases, while $15-25\%$ are weak acids.

Brønsted-Lowry Acid

A substance that can donate a proton ($H^+$).

Brønsted-Lowry Base

A substance that can accept a proton ($H^+$).

Strong electrolytes

Acids or bases that dissociate completely in water and exist entirely in their ionized form, such as $HCl$, $H_{2}SO_{4}$, and $NaOH$.

Weak acids and bases

Substances that only partially dissociate when added to water, forming an equilibrium among differing chemical species.

$K_{a}$ (Acid Dissociation Constant)

The equilibrium constant defined as $\frac{[H^+][A^-]}{[HA]}$; a larger value indicates a stronger acid that dissociates more readily into charged species.

Conjugate acid

The species formed (such as $BH^+$) when a base accepts a proton; it is the form capable of subsequently donating a proton.

Amphoteric

A term describing a substance, such as water, that has the ability to act as either an acid or a base.

Hydronium Ion

The species $H_{3}O^+$ formed when water acts as a proton acceptor (base) in the presence of an acid.

Conjugate acid-base pair

An acid and base that differ only by a single proton within an equilibrium relationship.

Weakly acidic functional groups

Common drug structural units including Carboxylic Acids, Phenols, Sulfonic Acids, Sulfonamides, and Thiols.

Aliphatic amines

Common weak base functional groups classified as Primary ($1^{\circ}$), Secondary ($2^{\circ}$), or Tertiary ($3^{\circ}$) depending on whether the nitrogen is bound to $1$, $2$, or $3$ carbons.

Aromatic amines

Functional groups where the nitrogen atom is attached directly to an aromatic ring.

Quaternary ammonium ion

A nitrogen-containing group that is considered an electrolyte but is neither acidic nor basic because it cannot accept or donate a proton.

Neutral functional groups

Functional groups that do not act as acids or bases, including Alcohols, Ketones, Aldehydes, Ethers, Esters, and Amides.

pH

The negative logarithm of the hydrogen ion concentration ($pH = -\log [H^+]$); a decrease in this value signifies an increase in hydrogen ion concentration.

pOH

The negative logarithm of the hydroxide ion concentration ($pOH = -\log [OH^-]$); the relationship to pH is maintained as $pH + pOH = 14$.

$$pK_{a}$$

The negative logarithm of the acid dissociation constant ($- \log K_a$); stronger acids have smaller values, while stronger bases (via their conjugate acids) have larger values.

Ion Trapping

A clinical phenomenon where changing the pH of a physiological compartment (like urine) favors the charged form of a drug to either increase its excretion or affect its absorption.

Sodium bicarbonate

An additive used to increase the pH of urine (alkalinization), which causes weak acids to be cleared more rapidly.

Ammonium chloride

An additive used to decrease the pH of urine (acidification), which causes weak bases to be cleared more rapidly.

Weak acid salt formation

The reaction of un-ionized weak acids with strong bases, most commonly Sodium Hydroxide ($NaOH$), to form salts like Sodium salts ($RCOO^-Na^+$).

Weak basic salt formation

The reaction of un-ionized weak bases with strong acids such as Hydrochloric, Tartaric, Succinic, or Maleic acid.