Acid-Base Theory Lecture Flashcards

Comprehensive vocabulary flashcards covering acid-base theories, physiological pH, functional group classifications, the pKa scale, and clinical applications like ion trapping and salt formation.

Homeostasis

The stable internal environment maintained by the body, which requires keeping fluid $pH$ within a narrow range for proper organ and cell function.

Normal Blood $pH$

A narrow range between $7.35$ and $7.45$, with a typical average of $7.4$.

Small-Molecule Drug Composition

The majority of marketed drugs behave in aqueous solutions as weak bases ($60-70 \%$) or weak acids ($15-25 \%$).

Brønsted-Lowry Acid

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

Brønsted-Lowry Base

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

Strong Electrolytes

Strong acids and bases (such as $HCl$, $H_2SO_4$, and $NaOH$) that dissociate completely in water and exist entirely in their ionized form.

Acid Dissociation Constant ($K_a$)

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

Conjugate Acid

The species formed when a base accepts a proton; for a weak base $B$, the conjugate acid is represented as $BH^+$.

Amphoteric

A substance, such as water ($H_2O$), that can act as either an acid (proton donor) or a base (proton acceptor).

Hydronium Ion

The chemical species $H_3O^+$ formed when water acts as a proton acceptor.

Conjugate Acid-Base Pair

An acid and a base that differ only by the presence or absence of a single proton ($H^+$).

Weak Acid Functional Groups

Chemical groups including Carboxylic Acids, Phenols, Sulfonic Acids, Sulfonamides, and Thiols.

Weak Base Functional Groups

Chemical groups including Aliphatic amines (Primary, Secondary, Tertiary), Aromatic amines, and Nitrogen-containing heterocycles.

Aliphatic Amines

Amines where the nitrogen is bound to carbons that are not part of an aromatic ring; classified as Primary ($1^{\circ}$, 1 carbon), Secondary ($2^{\circ}$, 2 carbons), or Tertiary ($3^{\circ}$, 3 carbons).

Aromatic Amines

Amines where the nitrogen is attached directly to an aromatic ring.

Quaternary Ammonium Ion

An electrolyte that is neither acidic nor basic because it cannot accept or donate a proton ($H^+$).

Neutral Functional Groups

Functional groups that do not behave as acids or bases, including Alcohols ($R-O-H$), Ketones, Aldehydes, Ethers, Esters, and Amides.

$$pH$$

The negative logarithm of the hydrogen ion concentration: $pH = -\log[H^+]$.

$$pOH$$

The negative logarithm of the hydroxide ion concentration: $pOH = -\log[OH^-]$. Note that $pH + pOH = 14$.

Sulfonic Acid $pK_a$ Range

A range of $-1$ to $1$.

Carboxylic Acid $pK_a$ Range

A range of $2$ to $6$.

Aromatic Sulfonamide $pK_a$ Range

A range of $6$ to $8$.

Aliphatic Amines $pK_a$ Range

A range of $8$ to $11$.

Anilines $pK_a$ Range

A range of $3$ to $5$.

Relationship between acid/base strength and $pK_a$

The stronger the acid, the smaller the $pK_a$; the stronger the base, the larger the $pK_a$.

Ion Trapping

A process where changing urinary $pH$ influences drug excretion by favoring the charged (less lipid-soluble) form; weak acids are trapped/excreted faster in alkaline $pH$, and weak bases are trapped/excreted faster in acidic $pH$.

Sodium Bicarbonate

An additive used to increase the $pH$ of urine, thereby increasing the clearance of weak acids like Salicylates or Phenobarbital.

Ammonium Chloride

An additive used to decrease the $pH$ of urine, thereby increasing the clearance of weak bases like Amphetamine or Quinine.

Weak Acid Salts

formed by reacting a weak unionized acid (like Carboxylic acid) with a strong base such as Sodium Hydroxide ($NaOH$), Potassium Hydroxide, or Ammonium Hydroxide.

Weak Base Salts

formed by reacting a weak unionized base (like an amine) with strong acids such as Hydrochloric ($HCl$), Sulfuric, Nitric, Tartaric, Succinic, Citric, or Maleic acid.