Unit 5: Equilibrium
Section 12.2 pH and pOH
With the electrolytic dissociation of an ________ or a _________, equilibrium will
be established. The quantification of the acidity of the solution, that is the
concentration of ___ ions, is called the _____. The ____ scale goes from ___ to
____. The concentration of _____ ions in solution is called the ____.
Since the measurement of [H+] ions can vary from say small concentrations, say
_______________________, (__________) and very large concentrations, say
_________, (________) for convenience the scale needs to be _____________.
____ = pH value
____ = Hydronium ion concentration in _______
____ = pOH value
____ = Hydroxide ion concentration in _______
Example A Find the pH of a solution with an H3O+ concentration of 4.7x10-11
mol/L. Is the solution acidic or neutral?
Example B Determine the [OH-] given a pOH of 3.60.
Unit 5: Equilibrium
pH and pOH Practice
a) What is the pH of a solution that
contains 1.0 x10–2 M of H+?
b) What is the pH of black coffee at
25oC if [OH-] is 2.0 x 10-10 M?
c) What is the pH of a solution that
contains 5.0 x10–12 M of H+?
d) A solution of 0.09M NH3 is prepared
in water at 25oC. What is the pH?
e) What is the pH of a solution that
contains 1.0 x10–7 M of H+?
f) What is the [H+] of a solution if the pH
is 3.7?
g) What is the pOH and pH of a solution h) What is the [H+] of a solution if the pH
that contains 6.4 x10–10 M of OH-?
is 9.62?
i) A solution of 0.25M HCN (Full
dissociation) is prepared in water at
25oC. What is the pH of the solution?
pOH?
j) What is the [OH-] of a solution if the
pOH is 5.4?
Unit 5: Equilibrium
Section 12.2 Calculations with Ka and Kb
Recall that ____ and ____ are the equilibrium constants for acids and bases in
solution respectively.
If Ka or Kb is >> 1 the solution contains a ______________ acid or base. _____
If Ka or Kb is << 1 the solution contains a ______________ acid or base. _____
Example A Calculate the Ka of a 0.10 M CH3COOH solution if the concentration
of [H3O+] and the concentration of [CH3COO-] is 1.34 x 10-3 M.
Example B Calculate the [H3O+] & the pH of a 0.25 M solution of CH3COOH.
Ka = 1.80 x 10-5.
Unit 5: Equilibrium
Example C Determine the pH of an aqueous solution of formic (methanoic) acid
(HCOOH) at 0.2 mol/L, if the value of its acidity constant is 1.8 x 10-4.
Example D Ammonia dissolve in water to from ammonium hydroxide. The value
of the basicity constant is 1.8 x10-5. What is the pH of the ammonium hydroxide
solution at 0.40 mol/L?
NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq)
Hmwk: pg. 338-340 #3, 5-7, 21,23 & 25