Acids & Bases
Lesson 6
Strong Acid-Base Calculations
Strong Acids & Bases
Calculations
Strong Acids & Bases
Calculations
When we consider strong acids and bases, remember
this:
They ionize 100%
In other words, [strong acid] = [H3O+]
[strong base] = [OH-]
When you mix the acid with the base, consider which concentration of H3O+ or
OH- is in excess.
Strong Acids & Bases
Calculations
Part I: strong acid or strong base only in water
Part II: Mixing the strong acid and the strong
base together.
Part I: strong acid or strong base only in water
1.
Calculate the pH of 0.40 M HI.
HI

0.40 M
0.40 M
H+
pH = -Log[H+]
pH = -Log[0.40]
pH = 0.40
+
0.40 M
I-
2.
Calculate the pH of 0.030 M Ba(OH)2.
Ba(OH)2
0.030 M

Ba2+
+
0.030 M
2OH0.060 M
pOH = -Log[OH-]
pOH = -Log[0.060]
pOH = 1.22
pH + pOH = 14.00
pH + 1.22 = 14.00
pH = 12.78
Try: Calculate the pH of 0.020 M Mg(OH)2
3.
Calculate the pH of 100.0 mL of 1.0 M HCl after 300.0 mL of
water is added to it.
100
400

HCl
1.0 M
H+
0.25 M
pH = -Log[H+]
pH = -Log[0.25]
pH
=
0.60
+
Cl0.25 M
Try: Calculate the pH and pOH of 200.0 mL of 2.0 M
HCl after 300.0 mL of water is added to it.
Part II: Mixing solutions of the strong acid
and the strong base together.
Helpful hints:
-
Start as always by getting your [H3O+] And [OH-]
Hydronium ion and Hydroxide ion will neutralize each other, however if there is extra
of one of the two…
Find the excess/extra you have.
- If you have extra [OH-], your solution will be basic.
-
If you have extra [H3O+], your solution will be acidic.
Example: 200.0 mL of 0.200 M HCl is mixed with 400.0 mL of
0.250 M NaOH. Calculate the pH of the new solution.
TRY: calculate the final [H3O+], [OH-] and new pH in a solution formed when
150.0 mL of 1.5 M HNO3 is added to 250.0mL of 0.80 M KOH
example
How many moles of HCl(g) must be added to 40.0mL of 0.180 M NaOH to
produce a solution having pH= 12.500, if it is assumed that there is no change
in volume when the HCl is added?
TRY:
How many moles of HCl(g) must be added to 30.0mL of 0.170 M Ca(OH)2 to
produce a solution having pH= 10.500, if it is assumed that there is no change
in volume when the HCl is added?
Example: calculate the pH resulting from mixing 25.0 mL of
0.0420 M Ba(OH)2 with 125.0 mL of 0.0120 M HCl.
TRY: calculate the pOH resulting from mixing 50.0 mL of 0.0185 M Sr(OH)2 with
35.0 mL of a solution containing 0.130 g of HCl.
Ex:
A chemist has 2.000 L of 0.00120 M KOH soltuion. What mass of HCl(g)
would have to be added to the KOH solution to produce a solution having a pH of
10.857?
-assume no change in volume occurs.
Homework:
p.143
#58, 59, 62, 63, 64, 66,67.