Acid-Base Equilibria

What does the Arrhenius definition of an acid state?

An acid is a hydrogen-containing compound in an aqueous solution that ionizes to yield hydrogen ions (H+).

What does the Arrhenius definition of a base state?

A base is a compound that ionizes to yield hydroxide ions (OH-) in an aqueous solution.

According to Bronsted-Lowry theory, what is an acid?

A hydrogen-ion (or proton) donor.

According to Bronsted-Lowry theory, what is a base?

A hydrogen-ion (or proton) acceptor.

What is the general reaction equation for an acid reacting with water?

Acid + water → acid-anion + hydrogen-anion (HA + H2O → H+ + A-).

What is the general reaction equation for a base reacting with water?

Base + water → hydroxide-ion + base-cation (B + H2O → OH- + B+).

What defines a conjugate acid-base pair?

A conjugate acid-base pair consists of an acid and its conjugate base that are related through the donation and acceptance of a proton.

What does the self-ionization of water involve?

One water molecule donates a hydrogen ion to another water molecule, establishing a dynamic equilibrium.

What is the equilibrium constant expression for water?

[H3O+] · [OH-] = Kc.

What is the specific ion-product constant for water represented by Kw?

Kw is the equilibrium constant for the self-ionization of water.

What is the fundamental role of pH indicators?

They change color depending on the pH of the solution due to their weak acid or base nature.

What is the reaction equation for an indicator in acid form?

Hln (acid form) ⇋ H+ + ln- (base form).

How do stronger acids and bases behave in solution?

Stronger acids and bases dissociate almost completely and have a low pKa or pKb.

What is a characteristic of weaker acids and bases?

Weaker acids and bases only partially dissociate and have a high pKa or pKb.

In titration of a strong acid with a strong base, what occurs at the equivalence point?

All hydronium ions have reacted with hydroxide ions, resulting in a neutralized salt solution.

How is pH calculated before the equivalence point in a strong acid-base titration?

pH = -log[H3O+].

What does the Henderson-Hasselbalch equation express?

The pH of a buffer system in terms of the concentrations of its acid and conjugate base.

How can you define buffer capacity?

The amount of acid or base that can be added to a buffer solution before a significant pH change occurs.

What happens to acid concentration when a base is added to a buffer?

The concentration of the acid decreases to neutralize the added base.

What types of solutions are typically used in buffer systems?

A mixture of a weak acid and its conjugate base or a weak base and its conjugate acid.

Give an example of a buffer system.

Ethanoic acid (CH3COOH) and ethanoate ion (CH3COO-).

What does the base dissociation constant (Kb) indicate?

The extent to which a base dissociates in water.

What does the term 'strong acid' refer to?

An acid that dissociates completely in solution.

What is the pKa value of a stronger acid compared to a weaker acid?

A lower pKa indicates a stronger acid that dissociates more in water.

What is the significance of the half-equivalence point in titrations?

At the half-equivalence point, the concentration of the acid equals that of the conjugate base.

How can you assess whether an acid is strong or weak based on its dissociation?

By examining its pKa; a lower pKa means a stronger acid.

What is the equation for calculating the pH from the concentration of hydronium ions?

pH = -log[H3O+].

What happens to the pH after the equivalence point in a titration?

The solution becomes increasingly basic since there are no more H3O+ ions left to react.

What important role do buffers play in biological systems?

They help maintain stable pH levels despite the addition of acids or bases.