Acid-Base
Acid-Base
Acid-Base
Introduced in 1887
Acids are substances that dissociate in
water to yield electrically charged atoms
or molecules, called ions, one of which is
a hydrogen ion (H +)
Bases ionize in water to yield hydroxide
ions (OH −).
Lewis theory
Lewis Bases donate pairs of electrons
and acids accept pairs of electrons.
Lewis acid is therefore any substance,
such as the H+ ion, that can accept a pair
of electrons.
In other words, a Lewis acid is an
electron-pair acceptor.
Lewis base is electron-pair donor.
Lowry Bronsted theory
Brønsted–Lowry theory, also called proton
theory of acids and bases,
Introduced independently in 1923 by the
Danish chemist Johannes Nicolaus
Brønsted and the English chemist Thomas
Martin Lowry,
Compound that can transfer a proton to any
other compound is an acid
Compound that accepts the proton is a
base.
Weak and strong acids
Extent of dissociation decides the
strengt of acids and bases
Strong acids dissociate completely
Weak acids ionise incompletely
Strong acid- HCl
Weak acid – Acetic acid
Dissociation constant
pH
Negative log of the hydrogen ion concentration
pH= pK + log([base or salt]/[acid])
Represents the hydrogen concentration
Terms
Buffer
Combination of a weak acid and /or a weak
base and its salt
What does it do?
Resists changes in pH
Effectiveness depends on
pK of buffering system
pH of environment in which it is placed
Buffer action
Acid-Base Balance
Function
Maintains pH homeostasis
Maintenance of H+ concentration
pH
Normal and abnormal pH
Normal pH is 7.35-7.45
Acidosis
pH less than 7.35
CNS depression or coma
Alkalosis
pH greater than 7.45
Tetany, neuro muscular hyperexcitability
Regulation of pH
Direct relation of the production and retention of acids and
bases
Systems
Respiratory Center and Lungs
Kidneys
Buffers
Found in all body fluids
Weak acids good buffers since they can tilt a reaction
in the other direction
Strong acids are poor buffers because they make the
system more acid
19
Blood Buffer Systems
When an acid enters the ECF: When an alkali enters the ECF:
O2(Oxygenation)
Fe++ O2 (Deoxygenation)
N
e- R
N+
Acts as ‘acid’ +Acts as ‘base’
and gives up H+ H and takes up
‘proton’ ‘proton’
Lungs Tissues
Venous circulation
HCO3-
HCO3- HCO3-
HHb HHb
HHb
O2
O2
H+
H+
H2CO3
H2CO3
H2O H2O
CO2 CO2
Expired air
Metabolism
Role of Lungs in acid-base
balance
Respiratory centre – medulla
Sensitive to even slight changes in pH
and pCO2
Blood pCO2 – 1.5mmHg – 100%
stimulation of resp. centre
in pulmonary ventilation
Excess CO2 is removed from ECF
Role of Lungs in acid-base
balance
CO2 CO2
HCO3- HCO3-
H+ H+ H2CO3
NaHCO3
Na+
Na+ Na+ Na+ + HCO3-
Sodium pump
(active transport) Passive diffusion NaHCO3
Bicarbonate mechanism
Phosphate mechanism
Urine pH can become as low as 6 to
4.8
Operates in distal tubules of kidney
Phosphate mechanism –
working model
Distal tubular epithelial cells
Blood Tubular filtrate
Metabolic
CO2 CO2
H2 O H2O H2CO3
HCO3- HCO3-
H+ H+ NH4+
NaHCO3
Na+
Na+ Na+ Na+ + Cl-
Sodium pump Passive diffusion
(active transport)
NH4Cl
Ammonia mechanism
Excreted in urine