Ionic Equilibria Lecture Flashcards

This set of vocabulary flashcards covers the fundamental concepts of ionic equilibria, including theories of acids and bases, dissociation constants, Ostwald's dilution law, pH/pOH scales, salt hydrolysis, buffer solutions, and solubility products.

Ionic Equilibrium

The equilibrium between ions and unionized molecules in solution.

Electrolytes

Substances which give rise to ions when dissolved in water.

Strong electrolyte

Electrolytes that ionize completely or almost completely in dilute aqueous solutions, such as strong acids, strong bases, and salts.

Weak electrolyte

Electrolytes which dissociate to a smaller extent and only partially in dilute aqueous solutions, establishing an equilibrium between ions and nonionized molecules.

Degree of dissociation ($\alpha$)

The fraction of total number of moles of the electrolyte that dissociates into its ions when the equilibrium is attained, calculated as $\frac{\text{number of moles dissociated}}{\text{total number of moles}}$.

Arrhenius Acid

A substance which contains hydrogen and gives rise to $H^+$ ions in aqueous solution.

Arrhenius Base

A substance that contains an $OH$ group and produces hydroxide ions ($OH^-$) in aqueous solution.

Bronsted-Lowry Acid

A substance that donates a proton ($H^+$) to another substance.

Bronsted-Lowry Base

A substance that accepts a proton ($H^+$) from another substance.

Conjugate acid-base pair

A pair of an acid and a base differing by a single proton ($H^+$).

Lewis Acid

Any species that accepts a share in an electron pair.

Lewis Base

Any species that donates a share in an electron pair.

Amphoteric nature of water

The ability of water to act as both an acid (towards bases like $NH_3$) and a base (towards acids like $HCl$).

Acid-dissociation constant ($K_a$)

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

Base-dissociation constant ($K_b$)

The equilibrium constant for the dissociation equilibrium of a weak base, represented as $K_b = \frac{[B^+][OH^-]}{[BOH]}$.

Ostwald's dilution law

A quantitative expression of the Arrhenius concept stating that the degree of dissociation of a weak electrolyte is inversely proportional to the square root of its concentration (e.g., $\alpha = \sqrt{\frac{K_a}{c}}$).

Ionic product of water ($K_w$)

The product of molar concentrations of hydronium ions and hydroxyl ions at equilibrium in pure water; at $298\,K$, $K_w = 1.0 \times 10^{-14}$.

pH

The negative logarithm to the base 10 of the concentration of $H^+$ ions in solution in $mol\,dm^{-3}$, mathematically expressed as $pH = -\log_{10}[H^+]$.

pOH

The negative logarithm to the base 10 of the molar concentration of $OH^-$ ions in solution, expressed as $pOH = -\log_{10}[OH^-]$.

Hydrolysis of salt

The reaction in which cations or anions (or both) of a salt react with ions of water to produce acidity, alkalinity, or sometimes neutrality.

Buffer solution

A solution which resists drastic changes in pH when a small amount of strong acid, strong base, or water is added to it.

Acidic buffer solution

A solution containing a weak acid and its salt with a strong base, such as $CH_3COOH$ and $CH_3COONa$.

Basic buffer solution

A solution containing a weak base and its salt with a strong acid, such as $NH_4OH$ and $NH_4Cl$.

Henderson-Hasselbalch equation

Equations used to calculate the pH or pOH of buffer solutions, such as $pH = pK_a + \log_{10}\frac{[\text{salt}]}{[\text{acid}]}$.

Molar solubility

The number of moles of a compound that dissolve to give one litre of saturated solution, calculated as $\frac{\text{solubility in g/L}}{\text{molar mass in g/mol}}$.

Solubility product ($K_{sp}$)

The product of equilibrium concentrations of the constituent ions in a saturated solution, each raised to the power equal to its coefficient in the balanced equilibrium expression.

Ionic product (IP)

The product of concentrations of constituent ions under any condition; if $IP > K_{sp}$, precipitation occurs.

Common ion effect

The suppression of the ionization of a weak electrolyte in the presence of a strong electrolyte containing an ion common to the weak electrolyte.