1. CLASSICAL ACID-BASE DEFINITION (ARRHENIUS) 2. THE BRONSTEDLOWERY ACID –BASE 3. THE LEWIS ACID-BASE 4. THE IONIZATION OF WATER , ACID AND BASE

1. I O N I C EQUILIBRIA
PHYSICAL PHARMACY I
LEC 4
ASSISTANT LECTURER
DR AHMAD A YOSEF
MSC PHARMACEUTICAL SCIENCES

2. Acids/ Base
1 DEFINITION
Ionization
2
Sorensen's pH
3
PBE
4
Contents

3. • Acid:- is a substance that has H in its formula and dissociates
in water to yield H3O +
,
• ex: HCl ,HNO 3
.
• Base :- is a substance that has OH in its formula and
dissociates in water to yield OH -
,
• ex: NaOH ,KOH and Ba(OH) 2
.
1
. CLASSICAL ACID-BASE DEFINITION
(ARRHENIUS.)
3

4. • Acid:- is a proton donor , any species that donates an H ion ,An
acid must contain H in its formula: HNO3and H2PO4 - are two of
many examples.
All Arrhenius acids are Bronsted-lowery acids.
• Base:- is a proton acceptor ,any species that accepts an H ion.
A base must contain alone pair of electrons to bind the H + ion .
few example are : NH3 , Co2-2, F- as well as OH -
.
2
. THE BRONSTED-
LOWERY ACID –BASE
DEFINITION
4

5. Solvents can be classified as protophilic, protogenic,
amphiprotic, and aprotic.
1. A protophilic or basic solvent is one that is capable of
accepting protons from the solute. Such solvents as acetone,
ether, and liquid ammonia NH 3
.
2. A protogenic solvent is a proton-donating compound and is
represented by acids such as acetic acid CH3COOH, sulfuric
acid, liquid HCl, and liquid HF.
3. Amphiprotic solvents act as both proton acceptors and proton
donors, e.g water H2O and the alcohols.
4. Aprotic solvents, neither accept nor donate protons, and, being
neutral in this sense, such as the hydrocarbons (e.g. CH 4
)
TYPES OF SOLVENT
5

6. 3
. THE LEWIS ACID-BASE
DEFINITION.
 Acid:- is any species that accepts an electron pair.
 BF3, ALCl3 and metal cation (M 2
+ .)
,
 Base:- is any species that donates an electron pair ,NH3 ,
C2H5‒O‒C2H 5
.
 In the Bronsted-lowery ,reaction involve Transfer of a proton,
they known as aprotolytic reactions or protolysi
6
s.

7. IONIZATION OF WEAK
ACIDS
7

8. 8

9. • The basicity constant Kb is expressed as:
IONIZATION OF WEAK
BASES:
9

10. THE IONIZATION OF WATER
10

11. 11

12. The autoprotolytic constant or ion product of water.
Kw=[OH-] [H3O]
=
1
×
10
-
14
………
. at 25 ⁰C
In pure water:
A simple relationship exists between Ka of weak acid (HB) and Kb
of its conjugate base (B-), and between Ka of BH+ and Kb of B
when the solvent is amphiprotic (e.g. water)
Ka Kb =Kw
Ka =Kw/Kb ,Kb =Kw /Ka
12

13. EXAMPLE

14. ACIDS THAT DONATE A SINGLE PROTON AND
BASES THAT ACCEPT A SINGLE PROTON ARE
CALLED MONOPROTIC ELECTROLYTES.
A polyprotic (polybasic) acid is one that is
capable of donating two or more protons, and a
polyprotic base is capable of accepting two or
more protons.
A diprotic (dibasic) acid, such as carbonic acid H2CO3,
ionizes in two stages, and a triprotic (tribasic) acid, such
as phosphoric acid H3PO4, ionizes in three stages.
A species that can be function either as an acid or base also
called amphoteric in nature. Ex. Amino acids and proteins

16. • demonstrated that in the phosphoric acid system, the species
H2PO4- and HPO42- can function either as an acid or a base.
• A species that can be function either as an acid or base also called
amphoteric in nature.
• Ex. Amino acids and proteins. If glycine hydrochloride is dissolved in
water , it ionizes as follow
• The species +NH3CH2COO- is amphoteric in that, in addition to
reacting as an acid as shown , it can react as a base with water as
follows:
AMPHOLYTES
16

17. 17
• The amphoteric species +NH3CH2COO- is called a zwitterion
and differs from the amphoteric species formed from
phosphoric acid in that it carries both a positive and a negative
charge, and the whole molecule is electrically neutral.
• The pH at which the zwitterion concentration is a maximum is
known as the isoelectric point. At the isoelectric point the net
movement of the solute molecules in an electric field is
negligible.

18. 18

19. 19

20. 20
• The pH of a solution can be considered in terms of a numeric scale
having values from 0 to 14, which expresses in a quantitative way the
degree of acidity (7 to 0) and alkalinity ( 7-14
.)
• The value 7 at which the [H+] =[OH-] at room temperature is referred
to as the neutral point, or neutrality. The neutral pH at 0°C is 7.47,
and at 100°C it is 6.15 (Table 7-3
.)

21. 21

22. The term ‘p’ ia also express the negative logarithm of each
[OH-], Ka, Kb, Kw as pOH, pKa, pKb and pKw
pKw =pOH + pH
pKw = pKa + pKb
pKa and pKb values provide a mean of comparing the strength
of weak acids and weak bases:
Lower pKa values corresponds to stronger acids
Lower pKb values corresponds to stronger bases
PKA, PKB, AND PKW
22

23. CALCULATION OF PH
23

24. PBE
(d)Each species in the PBE should be multiplied
by the number of protons lost or gained when it
is formed from
the starting species.
(e)Add [H3O+] to the left side of the equation
and [OH−] to the right side of the equation. These
result from the interaction of two molecules of water,
as shown previously.
(a) Always start with the species added to water.
(b)On the left side of the equation, place all
species that can form when protons are
consumed by the starting species.
(c)On the right side of the equation, place all
species that can form when protons are
released from the starting species.
The general method for obtaining the PBE is as follows:

25. EXAMPLES
26

26. EXAMPLE:
What is the
PBE when
Na2HPO4 is
added to
water?
]H3O+]+[H2PO4-]+2[H3PO4] = [OH-]+[PO 4 3
-
[
Na2HPO4 2Na + HPO4 2-
HPO4 2- + H2O PO4 3- +H3O+
HPO4 2- + H2O H2PO4 - + OH-
H2PO4 - + H2O H3PO4 + OH-

27. EXAMPLE:
What is the
PBE when
sodium
acetate is
added to
water?
[H3O+]+[CH3COOH] = [OH -
[
CH3COONa Na+ + CH3COO-
CH3COO- + H2O CH3COOH +OH-