DE_Chem_5.3.3

DE_Chem_5.3.3_What Are the Similarities and Differences between Acid and Base Strength and Concentration?

​According to the Arrhenius definition of acids and bases, the strength of an acid or base is defined as the degree of ionization or dissociation of the acid or base in aqueous solution

​Dissociation is the process by which a substance breaks up into smaller particles

​All acids dissociate, but only some will ionize.

​The strengths of acids and bases can be measured using the equilibrium constant expressions K_a (for acid strength) and K_b (for base strength).

​Strong acids and bases dissociate almost completely in water

Weak acids and bases dissociate slightly in water

​HA = H+ + A-

​Ka = [H+][A-]/[HA]

​strength can be determined by finding the acid dissociation constant (Ka).

​strength can be determined by finding the base dissociation constant (Kb)

​B = OH- + BH+

​Kb = [HB+][OH-]/[B]

​If the acid or base does not completely dissociate, then the strength can be determined by finding the acid or base dissociation constant

​According to the Brønsted-Lowry definition of acids and bases, an acid that loses a proton during dissociation is called a conjugate base. A base that gains a proton during dissociation is called a conjugate acid

​The stronger an acid is, the weaker its conjugate base is. While the stronger a base is, the weaker its conjugate acid.

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​some substances may act as either an acid or a base; it depends upon what other substances are around them. These substances are said to be amphoteric

Multiple Choice

Why is it important to distinguish between acid/base strength and concentration when studying acids and bases?

• Because strength and concentration are always the same

• Because strength refers to how much acid or base is present

• Because strength refers to the degree of dissociation, while concentration refers to the amount of solute

• Because concentration determines the pH directly

Multiple Choice

Which of the following statements correctly describes the relationship between the strength of an acid and its conjugate base according to the Brønsted-Lowry model?

• A strong acid has a strong conjugate base

• A strong acid has a weak conjugate base

• A weak acid has a weak conjugate base

• A weak acid has a strong conjugate base