1. ACIDS AND
BASES
(The pH and pOH
Concepts)

2. OBJECTIVES OF
THE LESSON:
At the end of the lesson, the
students are expected to:
 Identify a pH value as
acidic, neutral, or basic;

3. 2. Solve problems
correctly involving
pH, pOH, H and
+
OH ;-

4. 3. Cite some practical
importance of
knowing the pH of
substances.

5. pH= -log [H ] +
For coffee it’s 5; for
tomatoes it’s 4;
While household ammonia’s
11 or more.
It’s 7 for water, if in a pure
state,

6. But rainwater’s 6 and
seawater’s 8.
It’s basic at 10, quite
acidic at 2,
And well above 7 when
litmus paper turns blue.

7. Some find it a
puzzlement.
Doubtless their fog
Has some thing to do
with that negative
log!

8. pH OF THE SOLUTION
“ power of hydrogen”
 The negative logarithm
of the hydrogen ion
concentration.
 pH= -log [H+]

9. The concentration of hydrogen
ion in a solution is a measure of
its acidity or basicity.
The pH value is the negative
power to which 10 must be raised
to give the hydrogen ion
concentration.
[H+]= 10 –ph
M

10.  In a neutral solution, [H ]=
+
[OH] and a pH of 7 at 25 C.
o
 In an acidic solution,
[H ]>[OH] and has a pH of
+
less than 7.
 A basic solution has a pH of
greater than 7; [H ]< [OH].
+

11. pOH of the SOLUTION
 The negative logarithm of the
hydroxide ion concentration.
pOH= -log [OH ] -
 A neutral solution has a pOH of 7 at
25oC, the pOH of an acidic
solution is greater than 7, and the
pOH of a basic solution is less
than 7.

12. The pH Scale
 It was proposed in 1909 by the Danish
biochemist S.P.L. Sorensen, to describe
the degree of acidity or basicity.
 It ranges from 0-14
 The neutral point on the scale is 7.
 Values below 7 indicate increasing
acidity and those below 7 indicate
basicity.

13. pH + pOH= 14.00
pH = 14 - pOH
pOH = 14 - pH

14. pH VALUES OF COMMON
SUBSTANCES
SUBSTANC pH SUBSTANC pH
E E
1 M HCl 0 Coffee 5.1
Gastric 1.6-1.8 Urine 6.1
juice
Kalamansi 2.2 Milk 6.3-6.6
Vinegar 2.4-3.4 Blood 7.4

15. pH VALUES OF COMMON
SUBSTANCES
SUBSTANC pH SUBSTANCE pH
E
Apple 3.0 Baking Soda 9
Carbonated 3.1 Detergent 9.5-10
drink .5
Orange 3.5 Ammonia 11
Tomato 4.2 1 M NaoH 14

16. SAMPLE EXERCISES:
 The concentration of the
HCl secreted by the
stomach after a meal is
about 1.2 x 10 M. What
-3
is the pH of stomach
acid?

17. 2. Calculate the pH of a
0.10M of nitric acid and
of 0.10 M solutions of
acetic acid (1.3% ionized)
and nitrous acid (6.5 %
ionized).

18. 3. Water in equilibrium with
air contains 4.4x 10 % -5
carbon dioxide. The
resulting carbonic acid gives
the solution a [H ] of 2.0
+
x10 M, about 20 times
-6
larger than that of pure
water. Calculate the pH of
the solution.

19. 4. Calculate
the [H+] of a solution
whose pH is 9.
pH= -log [H ]
+
log [H ]= -9.0
+
[H ]= 10 or [H ]=antilog of
+ -9.0 +
-9.0
[H ]= 1x10 M
+ -9

20. 5. What are the pOH and pH of a 0.0125 M
solution of potassium hydroxide?
pOH= -log [OH-]
= -log (0.0125)
= -(-1.9)
pOH = 1.9
pH + pOH = 14
pH = 14 – pOH
= 14- 1.9
pH = 12.1