1. Medical Biochemistry Department
pH and Buffers By
All Staff Members of
Medical Biochemistry Department

2. Identify different pH solutions
By the end of this topic, the student will be able to:
Identify different pH solutions

3. 1-PH
Term of pH and its importance
pH scale
principles of water dissociation and Kw applications in calculating pH
2-Acid and Bases, general properties
Definition
General properties
Classification (strong , weak) with part B
3 MEASURING THE pH
Indicators
PH Meter

4. Term of pH and its importance
pH is a measure of the acidity or alkalinity of an aqueous solution.
pH Level - Similar to the body temperature, which has to be maintained; the pH level in the various body fluids are kept at a narrow range for the metabolic reactions to proceed properly.

5. pH scale ranges from 0 – 14 pH < 7 acid pH = 7 neutral2 3 4 5 6 7 8 9 10 11 12
acidic
(H+) > (OH-)
Neutral 25oC
(H+) = (OH-)
distilled water
basic or alkaline
(H+) < (OH-)
ranges from 0 – 14
pH < 7 acid
pH = 7 neutral
pH > 7 base

6. Water has limited capacity to dissociate (ionize) into H+ & OH-
Dissociation Of Water
H2O
H+ + OH-
Water has limited capacity to dissociate (ionize) into H+ & OH-

7. Ka Is The Dissociation Constant Of Water
[H2O]
[H+] [OH-] = Ka
Since water is too little dissociated
So,
Ka X [H2O] = Kw
[H+] [OH-] = Kw
10-7 X 10-7 = Kw
= mol/L
Kw = The Ion Product Of Water

8. The probability that hydrogen exist in water as ion = 1.8 x 10-9
The number of moles in one litre (1000 g) of H2O is
= Weight in g/ Molecular weight
So, (1000 g) / (18 g mol–1) = 55.5 mol.
The molar concentration of [ H+] = The probability that hydrogen exist in water as ion X molar conc. of water
= 1.8 x 10-9 x 55.5 = 99.9x 10-9 ~ 102x 10-9= 10-7 mol/L
The probability that hydrogen exist in water as ion = 1.8 x 10-9

9. Sorensen (1909) suggested that the
Since those values involving such –ve powers of 10 which is difficult to use in calculations So
Sorensen (1909) suggested that the
[H+]concentration of DILUTE aqueous solutions
would be better expressed as PH value

10. What is pH?
The pH of a solution is the negative of the logarithm to the base 10 of its hydrogen ion concentration in (mol/L)
pH = -log[H+]

11. pH= -log of H+ Concentration
P= -Log
H= H+ Concentration
pH= -log of H+ Concentration

12. [OH-] may be represented as pOH value
P= -Log
OH= [OH- Concentration]
pOH= -log of [OH- Concentration]

13. Since [H+] x [OH-] =10 -14 –log [H+] + -log [OH-] =14
By –log of both sides
–log [H+] + -log [OH-] =14
i.e. pH + pOH =14

14. Q- What is the pH of 0.0001 N HCL sol.?
A- [H+] = = mol/L
pH = - log = 4
Q - What is the pH of N NaOH sol.?
A- [OH-] = = mol/L
pOH = - log = 3
Since pH+ pOH=14
So, pH = 14 - pOH= 14 -3= 11

15. Acids and bases 1-Definition 2-Properties 3-Classification
4-Neuteralization

16. Acids and bases Acids Bases Taste sour Taste bitter
Turn blue litmus paper red
form hydrogen ions (H+) in water
Bases
Taste bitter
Turn red litmus paper blue.
form hydroxide ions in water

17. Bases cause OH- to increase
Acids cause H+ to increase

18. Amphoteric Substance
They can act as Proton DONORS with bases & Proton ACCEPTORS with acids Eg. Amino acid –H2O

19. In dilute aqueous solution, as [H+] increases:
A. pH decreases
B. pOH increases
C. [OH–] decreases
D. all of the above

20. Determining pH
1-Indicators
2-pH Meter

21. Indicators
Compounds that change color when in contact with an acid or base
They might be in the form of
Solutions or litmus paper

22. How Simple Indicators Work?

23. Mechanism of action of the litmus paper indicator
indicator act as acid and loss protons
ionized form
Blue color
In basic solutions
indicator act as bases and accept protons
mostly non-ionized form
Red color
In acidic solutions
ionized form+non-ionized form
no change in color in litmus paper or Intermediate color in other indicators
In intermediate pH

24. Different Indicators

25. pH meter
Much more precise method

26. Neutralization HCl + NaOH → H2O + NaCl reaction between an acid & base
acid base water salt
reaction between an acid & base
produces water & a salt
an ionic compound

27. Lab activities
3.understand the concept of neutralization reaction (home activity )
2.Demonstrate how indicators can be used to test for the presence of acids or bases and the effect of pH on them
1.Identify the pH of different solutions using litmus paper indicator

28. home activity Observe? and Explain
Add a spoon of vinegar
Concentrated
Baking Soda solution
Observe? and Explain
In half a glass of water, put a few teaspoons of baking soda and mix in order to obtain a quite concentrated solution. In the same glass, pour a spoon of vinegar.

30. Extended Modular Program