(2.8) Strength of Acids and Bases (pp. 664-669)
How do acid dissociation constants vary between strong acids and weak acids?
A strong acid is completely ionized in aqueous solution and has a large Ka. A weak acid is ionized only slightly in aqueous solution and has a small Ka.
Which of the acids in Table 19.6 would you expect to have the lowest dissociation constant?
hypochlorous acid
weak acid
ionizes only slightly in aqueous solution
weak base
reacts with water to form the conjugate acid of the base and hydroxide ions.
base dissociation constant (Kb)
the ratio of the concentration of the conjugate acid times the concentration of the hydroxide ion to the concentration of the base
acid dissociation constant (Ka)
the ratio of the concentration of the dissociated form of an acid to the concentration of the undissociated form.
How are acids and bases classified as either strong or weak?
Acids and bases are classified as strong or weak based on the degree to which they ionize in water.
A 0.500M solution of an acid has a hydronium-ion concentration of 5.77×10−6M Calculate the Ka of this acid.
Ka= 6.66x10^-11
How do you determine the Ka of a weak acid or the Kb of a weak base?
Substitute the measured concentrations of all the substances present at equilibrium into the expression for Ka or Kb.
What factor determines whether an acid or base is strong or weak?
The degree to which they ionize in water.
Acid HX has a very small Ka. How will the relative amounts of H+ and HX compare at equilibrium?
[HA] will be much greater than [H+] at equilibrium
strong acid
completely ionized in aqueous solution.
strong base
dissociates completely into metal ions and hydroxide ions in aqueous solution.
