Ionic Equilibria and pH Flashcards

Vocabulary flashcards covering ionic equilibria, autoionization of water, strong and weak acids/bases, Kw, Ka, Kb, and pH calculations based on the lecture material.

Autoionization of Water

The reaction in which water molecules ionize by transferring a proton to produce a hydronium ion ($H_3O^+$) and a hydroxide ion ($OH^-$), or dissociating into a hydrogen ion ($H^+$) and a hydroxide ion ($OH^-$).

Conjugate Acid

The species formed when a base gains or accepts a proton ($H^+$).

Conjugate Base

The species formed when an acid loses or donates a proton ($H^+$).

$K_w$ (Ionic Product of Water)

The equilibrium constant for the autoionization of water, defined mathematically as $K_w = [H^+][OH^-]$ or $K_w = [H_3O^+][OH^-]$.

Value of $K_w$ at RTP

The fixed numerical value of the ionic product of water at room temperature and pressure ($298\,K$), equal to $1 \times 10^{-14}\,mol^2\,dm^{-6}$.

Units of $K_w$

The unit of measurement for the ionic product of water, expressed as $mol^2\,dm^{-6}$ (or $mol^2\,dm^{-6}$).

Temperature Dependence of $K_w$

Since the autoionization of water is endothermic in the forward direction, increasing the temperature causes the equilibrium to shift forward, increasing the value of $K_w$.

pH

A measure of the hydrogen ion concentration in a solution, defined mathematically as $pH = -\log([H^+])$.

Formula for $[H^+]$ from pH

The mathematical expression used to calculate hydrogen ion concentration when pH is known: $[H^+] = 10^{-pH}$.

Neutral Solution

A solution in which the concentration of hydrogen ions ($[H^+]$) is exactly equal to the concentration of hydroxide ions ($[OH^-]$). At RTP, this corresponds to a pH of $7$.

Monoprotic Acid

An acid that releases or yields one mole of hydrogen ions ($H^+$) per mole of the acid upon complete dissociation.

Diprotic Acid

An acid that releases or yields two moles of hydrogen ions ($H^+$) per mole of the acid upon complete dissociation.

Monobasic Base

A base that yields one mole of hydroxide ions ($OH^-$) per mole of the base upon complete dissociation.

Dibasic Base

A base that yields two moles of hydroxide ions ($OH^-$) per mole of the base upon complete dissociation.

Strong Acid

An acid that fully or completely dissociates into its constituent ions in aqueous solution.

Strong Base

A base that fully or completely dissociates into its constituent ions in aqueous solution.

Weak Acid

An acid that only partially dissociates or ionizes into its ions in aqueous solution.

Weak Base

A base that only partially dissociates or ionizes into its ions in aqueous solution.

$K_a$ (Acid Dissociation Constant)

The equilibrium constant for the partial dissociation of a weak acid ($HA$), expressed as $K_a = \frac{[A^-][H^+]}{[HA]}$.

Units of $K_a$

The unit of measurement for the acid dissociation constant, expressed as $mol\,dm^{-3}$.

$K_b$ (Base Dissociation Constant)

The equilibrium constant for the partial dissociation of a weak base in water, expressed as $K_b = \frac{[\text{conjugate acid}][OH^-]}{[\text{weak base}]}$.

$$pK_a$$

The negative logarithm to base 10 of the acid dissociation constant, defined as $pK_a = -\log(K_a)$.

$$pK_w$$

The negative logarithm to base 10 of the ionic product of water, defined as $pK_w = -\log(K_w)$.

$$pOH$$

The negative logarithm to base 10 of the hydroxide ion concentration, defined as $pOH = -\log([OH^-])$.

Relationship between pH and pOH at RTP

The sum relationship of pH and pOH at room temperature and pressure ($298\,K$), expressed as $pH + pOH = 14$.