Chemistry Reference
In-Depth Information
Given: V
a
= 0.50 L; M
a
= 8.0 M; V
b
= 2.0 L
Find: M
b
Original Formula: V
a
M
a
= V
b
M
b
We can isolate the unknown, M
b
, by dividing both sides of the equation
by V
b
. Then we substitute, solve, and round, as shown here:
Given: V
a
= 0.50 L; M
a
= 8.0 M; V
b
= 2.0 L
Find:
M
b
V
a
M
a
V
b
(0.50 L)(8.0 M)
(2.0 L)
M
b
=
=
= 2.0 M
Of course, the titration formula can be used to determine the volume
of a solution with a known concentration needed to neutralize another
volume of a known concentration. Because this will be our third example
with this formula, I will risk solving Example 3 in one step. The only poten-
tially confusing aspect of this next problem will be that it involves the base
Ca(OH)
2
. Because Ca(OH)
2
releases two moles of OH
-
for every mole of
the base (as indicated by the subscript of “2” on the outside of the paren-
theses), we will multiply the molarity of the base by 2 in order to get the
molar concentration of the ions.
Example 3
How many liters of a 1.0 M Ca(OH)
2
solution would be required to
completely neutralize 3.0 L of a 2.0 M HCl solution?
Given: M
b
= 2.0 M; V
a
= 3.0 L; M
a
= 2.0 M
Find:
V
b
V
b
=
V
a
M
a
(3.0 L)(2.0 M)
2.0 M
=
= 3.0 L
M
b
Try the following practice problems and check your answers before
moving on to the chapter examination.
Lesson 9-6 Review
For the following titration reactions, assume the ionization of the acids
and bases are complete.
1.
How many liters of 3.0 M H
2
SO
4
would be required to completely neu-
tralize 2.0 L of 3.0 M NaOH?
2.
A student finds that it takes 150 ml of standard 3.0 M NaOH solution
to neutralize 450 ml of HCl. What is the molarity of the acid?
