Quantitative Chemistry 2nd quarter exam content

pH , ionic strengths and activities, monoprotic and polyprotic systems,

Define Acid dissociation constant

The acid dissociation constant, represented as $K_a$, is a measure of the strength of an acid in solution, defined as the ratio of the concentration of the dissociated ions to the undissociated acid at equilibrium.

Define base hydrolysis constant

The base hydrolysis constant, represented as $K_b$, is a measure of the strength of a base in solution, defined as the ratio of the concentration of the hydroxide ions produced to the undissociated base at equilibrium.

Define what a buffer is

A buffer is a solution that resists changes in pH when small amounts of acid or base are added, typically composed of a weak acid and its conjugate base, or a weak base and its conjugate acid.

What is buffer capacity?

Buffer capacity is the measure of a buffer solution's ability to resist changes in pH upon the addition of an acid or a base, often determined by the concentrations of the weak acid and its conjugate base.

What is the Henderson-Hasselbach equation?

The Henderson-Hasselbalch equation is a formula used to calculate the pH of a buffer solution, which relates the pH to the pKa of the weak acid and the ratio of the concentrations of the conjugate base and the weak acid.

pH= pka + log[a-]/{HA]

What are polyprotic acids and bases?

Polyprotic acids and bases are substances that can donate or accept more than one proton (H+ ion) per molecule during acid-base reactions. They have multiple ionization steps, each characterized by a distinct pKa value.

What are Zwitterions?

Zwitterions are molecules that contain both positive and negative charges, balancing each other out, and exist in a dipolar state. They are often found in amino acids, where the amino group is protonated and the carboxyl group is deprotonated.

What is an amphiprotic molecule?

An amphiprotic molecule is a species that can both donate and accept a proton (H+ ion) in chemical reactions. Common examples include water and amino acids, which can act as either acids or bases, depending on the circumstances.

What is the intermediate form of diprotic acid?

[H] = sqaure root (K{a1} \times K{a2}}{[F]} + K{1}K{w}/k{1}+F

What is the simplified form for solving the pH of the intermediate form of diprotic acid?

$pH = \frac{1}{2}$(pK_a1 + pK_a2)

what does mass balance equal to for monoprotic systems?

F= [HA]+ [A-]

Isoionic point:

the pH obtained when the pure, neutral polyprotic acid HA is dissolved in water.
[H]=

Isoelectric point

The pH obtained when the average charge of the polyprotic acid is 0.

Isoelectric point:

pH= (1/2) (pKa₁ +pK_a2)

What is the predominant form when pH<pk₁ in monoprotic and polyprotic species?

The predominant form is the fully protonated form (HA for monoprotic, HAn for polyprotic species), where the species retains all protons.

What is the predominant form when pK_a<pH<pk₂ in monoprotic and polyprotic species?

H_n-1A^- is favored over HnA, indicating partial deprotonation.

What is the predominant form when pH»pk₂ in monoprotic and polyprotic species?

The predominant form is the fully deprotonated form (A^- for monoprotic, A^n- for polyprotic species), where the species has lost all protons.