1. Water, pH and dissociation of water
DR.SADIA HAROON

2. Lecture 3 Outline Homeostasis The structure and function of water
Dissociation of weak acids and weak bases
pH and the Henderson-Hasselbalch equation
Buffers, biological/physiological examples

3. HOMEOSTASIS
The dynamic that defines the distribution of water and the maintenance of pH and electrolyte concentrations
Water distribution maintained by the kidneys, antidiuretic hormone, hypothalamic thirst response, respiration and perspiration
Clinically, need to be aware of water depletion caused by decreased intake (coma, wandering the desert) or increased loss (diarrhea, renal malfunction, over-exercise), and excess body water due to increased intake (too much I.V.) or decreased excretion (renal failure)

4. Importance of water 70% of earths surface is water Cell contains
Water is present intra cellular and extra cellularly
Water is essential for life
Chemical reaction takes place in aqueous environment

5. Water Chemistry All living organisms are dependent on water.
The structure of water is the basis for its unique properties.
The most important property of water is the ability to form hydrogen bonds.

6. Water Chemistry
Within a water molecule, the bonds between oxygen and hydrogen are highly polar.
Partial electrical charges develop:
- oxygen is partially negative
- hydrogen is partially positive

7. Water Chemistry
Hydrogen bonds are weak attractions between the partially negative oxygen of one water molecule and the partially positive hydrogen of a different water molecule.
Hydrogen bonds can form between water molecules or between water and another charged molecule.

9. Hydrophobicity/Micelles
From Lehninger, 2nd ed., Ch 4

10. Water Solubility / Hydrophilic
From Lehninger, 2nd ed., Ch 4

11. Water Chemistry

12. Structure of H20
From Lehninger, 2nd ed., Ch 4

13. Water Chemistry
The polarity of water causes it to be cohesive and adhesive.
cohesion: water molecules stick to other water molecules by hydrogen bonding
adhesion: water molecules stick to other polar molecules by hydrogen bonding

14. Water Chemistry

15. Structure of water Water has dipolar structure
V –shaped structure ,bend geometry
Two light atoms; hydrogen
One heavy atom oxygen
H-O-H
Angle between them109.47

16. Why ice floats on water It expands on freezing
It has density of 0.92g/ml
Water at 0 degree has density of 1.0 g/ml
Important in maintaining life and enviornment.

17. Structure of water
Hydrogen bonding :non covalent bonding between hydrogen and oxygen of two water molecules
Vander walls forces
Electrostatic interaction
Hydrophobic interactions; results in formation of droplet water water interaction)

18. Other properties of water
Thermal properties ;liquid at room temp
At 0 degree melts ,at 100 degree boils
Ice formation; maximum hydrogen bonding
Water vapour at 100 boiling

19. Properties of Water 1. Water has a high specific heat.
- A large amount of energy is required to change the temperature of water.
2. Water has a high heat of vaporization.
- The evaporation of water from a surface causes cooling of that surface.

20. Properties of Water 3. Solid water is less dense than liquid water.
- Bodies of water freeze from the top down.
4. Water is a good solvent.
- Water dissolves polar molecules and ions.

21. Other properties Solvent properties Remarkable solvent
Ionic substances and polar substances due to hydrogen bonding
Nonpolar lacks hydrogen bonding
Amphipathic rearrange to form micelles;non polar aggregate at centre non polar out side

22. Properties of Water 1. Water has a high specific heat.
- A large amount of energy is required to change the temperature of water.
2. Water has a high heat of vaporization.
- The evaporation of water from a surface causes cooling of that surface.

24. Hydrophilic/Hydrophobic
From Lehninger, 2nd ed., Ch 4

25. Water Chemistry

26. Water Chemistry

27. Properties of Water

28. Other properties Solvent properties Remarkable solvent
Ionic substances and polar substances due to hydrogen bonding
Nonpolar lacks hydrogen bonding
Amphipathic rearrange to form micelles;non polar aggregate at centre non polar out side

29. Ionization of water Water very less ionize [H+]+[OH-]
[H+]+[H2O]=H3O=hydronium ion
Hydrated proton
Ke=ionization constant of water
=[H+]+[OH-]/[H2O]
(1.8x10-16)(55.5)=1.0x10-14

30. Properties of Water 5. Water organizes nonpolar molecules.
- hydrophilic: “water-loving”
-hydrophobic: “water-fearing”
- Water causes hydrophobic molecules to aggregate or assume specific shapes.
6. Water can form ions.
H2O  OH H+1
hydroxide ion hydrogen ion

31. Ionization of water Water very less ionize [H+]+[OH-]
[H+]+[H2O]=H3O=hydronium ion
Hydrated proton
Ke=ionization constant of water
=[H+]+[OH-]/[H2O]
(1.8x10-16)(55.5)=1.0x10-14

32. pH =pH+pOH
The product of both ion s as gram mole in one liter of water is the ionic product of water.
P= -log (logarithm) to base 10
Log means ratio number
Log of a number is the index by which 10 is to be raised to get that number

33. Ionization of water Water very less ionize [H+]+[OH-]
[H+]+[H2O]=H3O=hydronium ion
Hydrated proton
Ke=ionization constant of water
=[H+]+[OH-]/[H2O]
(1.8x10-16)(55.5)=1.0x10-14

34. Ph scale Kw=[H+][OH-]=10-14 [H+]=[OH-]=10-7 pH =-log [H+]

35. Function of Water:
Most of cellular activities are performed in water solutions.

36. Body Fluid 4% TBW 40% TBW - makes up ~60% of total body weight (TBW)
- distributed in three fluid compartments.
16% TBW

37. 4% TBW
40% TBW
Fluid is continually exchanged between the three compartments.
16% TBW

38. 4% TBW
40% TBW
Exchange between Blood & Tissue Fluid
- determined by four factors:
capillary blood pressure
plasma colloid osmotic pressure
interstitium Hydrostatic Pressure
Interstitium colloid osmotic pressure
16% TBW

39. 4% TBW
40% TBW
Exchange between Blood & Tissue Fluid
- not affected by electrolyte concentrations
- Edema = water accumulation in tissue fluid
16% TBW

40. Water Gain Water is gained from three sources. 1) food (~700 ml/day)
2) drink – voluntarily controlled
3) metabolic water (200 ml/day) --- produced as a byproduct of aerobic respiration

41. Routes of water loss
1) Urine – obligatory (unavoidable) and physiologically regulated, minimum 400 ml/day
2) Feces -- obligatory water loss, ~200 ml/day
3) Breath – obligatory water loss, ~300 ml/day
4) Cutaneous evaporation -- obligatory water loss, ~400 ml/day
5) Sweat – for releasing heat, varies significantly

42. ACID-BASE BALANCE

43. Acid Base An acid is any chemical that releases H+ in solution.
A base is any chemical that accepts H+.

44. Acids and Bases
Most biological buffers consist of a pair of molecules, one an acid and one a base.

45. Acids and Bases Hydrogen ion (H+1) is the basis of the pH scale.
Greater H+1 concentration --- lower pH (acidic)
Lower H+1 concentration --- higher pH (basic)

46. pH
is the negative logarithm of H+ concentration, and an indicator of acidity.
  pH = - log [H+ ]
Example: [H+ ] = 0.1 M = 10 –7 M

47. pH
is the negative logarithm of H+ concentration, and an indicator of acidity.
  pH = - log [10 –7 ]
= 7 log 10 = 7
Example: [H+ ] = 0.1 M = 10 –7 M

48. pH  [ H+ ] =  pH  [ H+ ] =  pH
is the negative logarithm of H+ concentration, and an indicator of acidity.
  pH = - log [10 –8 ]
Example: [H+ ] = 0.01 M = 10 –8 M
= 8 log 10 = 8
0.01 M [ H+ ] = pH 8
0.1 M [ H+ ] = pH 7
 [ H+ ] =  pH
 [ H+ ] =  pH

49. Normal functions of proteins (especially enzymes) heavily depend on an optimal pH.
pH7.35-pH7.45

50. Acids and Bases Acid: a chemical that releases H+1 ions.
Base: a chemical that accepts H+1 ions.
Buffer: a chemical that accepts/releases H+1 as necessary to keep pH constant

51. Regulation of acid-base balance
1) Chemical Buffers
2) Respiratory Control of pH
3) Renal Control of pH

52. Properties of Water 1. Water has a high specific heat.
- A large amount of energy is required to change the temperature of water.
2. Water has a high heat of vaporization.
- The evaporation of water from a surface causes cooling of that surface.

53. Properties of Water 3. Solid water is less dense than liquid water.
- Bodies of water freeze from the top down.
4. Water is a good solvent.
- Water dissolves polar molecules and ions.

54. Acids and Bases Hydrogen ion (H+1) is the basis of the pH scale.
Greater H+1 concentration --- lower pH (acidic)
Lower H+1 concentration --- higher pH (basic)

55. Acids and Bases

56. Acids and Bases Acid: a chemical that releases H+1 ions.
Base: a chemical that accepts H+1 ions.
Buffer: a chemical that accepts/releases H+1 as necessary to keep pH constant

57. Acids and Bases

58. WATER
Comprises approx 70% of human mass (45-60% intracellular, 25% extracellular/blood plasma)
dipolar: partial negative charge on oxygen, partial positive charge on hydrogens
dipolar nature leads to formation of many low energy hydrogen bonds

59. Water Solubility / Hydrophilic
From Lehninger, 2nd ed., Ch 4

60. Hydrophilic/Hydrophobic
From Lehninger, 2nd ed., Ch 4

61. Hydrophobicity
From Lehninger, 2nd ed., Ch 4

62. Hydrophobicity/Micelles
From Lehninger, 2nd ed., Ch 4

63. Summary of water and pH relationship
Very low dissociation of H2O to H+ or OH-
The ion product of H2O, Keq X 55.5 M, leads to this: [H+] = [OH-] = 1 X 10-7 M for pure H2O which is a constant in biological systems
Therefore, if [H+] > 10-7 M, then [OH-] must be less than 10-7 M, and vice versa.
Thus, if the negative logarithm of [H+] is derived ( pH = -log [H+] ), pure water would be pH = 7, acids pH < 7, and bases pH > 7

64. Ionization properties of water
Water disociate

65. Polarity
Covalent bonds (electron pair is shared) between oxygen and hydrogen atoms with a bond angle of 104.5o.
Oxygen atom is more electronegative that hydrogen atom --> electrons spend more time around oxygen atom than hydrogen atom --> result is a POLAR covalent bond.
Creates a permanent dipole in the molecule.
Can determine relative solubility of molecules “like dissolves like”.

67. pH scale is widely used in biological applications
^pH 7is neutral ,means no acidity or
alkalinity
^when excess of H+ ions are added the solution are acidic
^when OH are added they become basic
^biomolecules have acidic or basic properties

69. The Relationship Between pH and pOH
[H+] mol/L
[OH-] mol/L 14
1.0
10-14 2 12
0.01
10-12 4 10
0.0001
10-10 6 8
10-6
10-8

73. pH measurement pH paper: 1.Broad range (1-14whole no)
2.Narrow range ( pH unit)
Universal indicator solution:
-It is a mixture of many indicators.
-Shows change of colour peculiar to the
composition of that mixture.
Litmus paper:
-Its neutral point is pH 7.
-Blue colour on alkaline side and red colour on acid side.

75. pH measurement pH meter: -Electrometric method with
automatic temp compensating
device.
-Precision potentiometer.
-Controlled dial is calibrated in pH
units & milli volts

77. pH measurement Calomel electrode: -It is used as reference electrode
Glass electrode: -glass separates two solutions of different H+ conc. A small potential arises across the membrane this is propotional to the difference in pH and can be measured by amplifier.

79. ACIDS AND BASES Acids are defined as hydrogen donor or proton donor.
Bases are defined as hydrogen acceptor
Strong acids and bases ionize completely in water.
HCl=H+ Cl and Na OH=Na+ OH
Strong acids are=sulfuric acid, nitric
Acid, hydrochloric acid and strong bases are Na OH and KOH.

81. ACIDS AND BASES Acids are defined as hydrogen donor or proton donor.
Bases are defined as hydrogen acceptor
Strong acids and bases ionize completely in water.
HCl=H+ Cl and Na OH=Na+ OH
Strong acids are=sulfuric acid, nitric
Acid, hydrochloric acid and strong bases are Na OH and KOH.

83. ACIDS AND BASES Acids are defined as hydrogen donor or proton donor.
Bases are defined as hydrogen acceptor
Strong acids and bases ionize completely in water.
HCl=H+ Cl and Na OH=Na+ OH
Strong acids are=sulfuric acid, nitric
Acid, hydrochloric acid and strong bases are Na OH and KOH.

85. Weak Acids and weak bases
Weak acids partially ionize to release a H+ ,and lower the pH.
Weak bases accept a H+ and increase the pH+

87. ACID BASE CONGUGATE PAIR

89. pH of various common fluids
Blood plasma
Liver
Muscle
Saliva
Urine
Orange juice
Vinegar
Gastric juice

91. Acids produce by the body
Carbonic acid
Sulphuric acid
Phosphoric acid
Lactic acid
Citric acid
Ammonium ion
Ketone bodies
-Acetoactic acid
-Betahydroxy butyric acid

93. Classification of acids
First is based on strength:
1.Strong acids:
-That ionizes completely.
-High concentration of H ions.
-Free H+ show less tendency to
combine with base. (weakest conjugate)
2.Weak acids:
-Slowly dissociates.
-Give less no of H+ ions.
-Has the strongest conjugate base.

95. Classification of acids
Second is based on
volatile/non-volatile:
1.Volatile acid:
-Carbonic acid:20000 m eq/day
2.Non-volatile acid:
-Lactic acid
-Sulphuric acid
-phosphoric acid

96. Classification of acids
Second is based on
volatile/non-volatile:
1.Volatile acid:
-Carbonic acid:20000 m eq/day
2.Non-volatile acid:
-Lactic acid
-Sulphuric acid
-phosphoric acid

97. From Devlin, 3rd ed., Ch 1

98. Dissociation Constant and pH
From Marks, Marks, Smith, Ch 4

99. Henderson-Hasselbalch Equation

100. From Devlin, 3rd ed., Ch 1

101. From Devlin, 3rd ed., Ch 1

102. Sample pH problems
From Devlin, 3rd ed., Ch 1

103. Sample pH Problem (cont)
From Devlin, 3rd ed., Ch 1

104. Buffers
Definition: A weak acid plus its conjugate base that cause a solution to resist changes in pH when an acid or base are added
Effectiveness of a buffer is determined by: 1) the pH of the solution, buffers work best within 1 pH unit of their pKa ) the concentration of the buffer; the more present, the greater the buffering capacity

105. Buffers and weak acids
Buffers are solutions that resist change in pH when acid or base is added to it.
It consist of weak acid and its salt (acetic acid and sodium acetate )or a weak base and its salt (ammonium hydro oxide and ammonium chloride )

106. Mechanism of buffer action
Added H+ ions = in the form of strong acid ,combine with anions A-( largely form the salt component of buffer), to form the weakely dissociable HA, so that pH does become as acid as it would be in the absence of the buffer.

107. Mechanism cont.. Acetic acid freely ionizable
Sodium acetate to a large extent
CH3COOH=CH3COO+H+
CH3COONa=CH3COO +Na+
H Cl is added acetate will combine with H+ to form acetic acid and NaCl is formed

108. Mechanism contd..
When NaOH is added the H+ of the buffer (acetic acid) combine with OH- to form water ,which is weakely dissociated .
Thus pH change due to base addition is also prevented by buffer
OH+H+ =H2O

110. BUFFERING CAPACITY
The efficiency of a buffer in maintaining a constant pH on the addition of acid or base is referred to as buffering capacity.
The capacity to combine with added acid remains so long as there is supply of the buffer salt in the medium.
OH can be buffered as long as some of the acid HA remains to supply the H+.

112. H-H EQUATION
The quantitative relationship between the concentrate of weak (HA) and its conjugate (A-) is Henderson equation.
HA=weak acid =H+ +A-
H+ =proton

114. H-H EQUATION
The quantitative relationship between the concentrate of weak (HA) and its conjugate (A-) is Henderson equation.
HA=weak acid =H+ +A-
H+ =proton

116. H-H EQUATION
Is important for under standing buffer action and acid –base balance in the blood and tissue.
Restating the expression for dissociation constant of an acid
The pH of a solution of a weak acid (or base) and its salt is given by
pH=pKa _log [HA/A-]

118. H-H EQUATION Ke =equilibrium constant K e =ionization constant
Or dissociation constant of an acid or Ka
Stronger acids :phosphoric acid, carbonic acid ,acetic acid have larger dissociation constant

120. Cont..
Weaker acids mono hydrogen PO4 have smaller dissociation constant
Pka=log 1/Ka
pKa =-logka
The stronger the tendency to dissociate a proton ,the stronger is the acid lower the pKa

122. H-H eq… Ka=[H+][A-]/HA First solve for [H+]=Ka [HA]/[A-]
Take neg log on both side log [H+]=-log Ka –log [HA]/A-
Putting values pH=pKa -log[HA]
pH=pKa+log[A-]/[HA]
pH=pKa

124. Determination of pH Take three test tubes
To one add 1ml sodium acetate+acetic acid=(log 1/10)=-1
10 ml both(log 10/10)=0
10ml Na acetate +1ml acid (log10/1)=1

126. Buffers of the body fluids
Intracellular buffers;phosphate buffers cossist of disodium hydrogen phosphate and sodium dihydrogen phosphate.
This has pka close to physiological ph
Pka=6.8

128. Contd. Protein buffers :depend on ionizable side chain
Histine imidazole group pka=6.1
16 histidine in albumin
38 histidine in haemoglobin

130. Buffers … Extracellular ;comprise43%(intracellular 57%)
65%=bicarbonate buffers
30%=haemoglobin
4%=protein
1%=phosphate buffers
Buffers are first line of defence against acid load

132. Bicarbonate buffer system
Consist of HCO3 and H2CO3
Most significant
65% of plasma buffering
40% of buffering of body
CO2 andHCO3 can diffuse easily across membranes
HCO3 (Metabolic component) regulated by kidney and co2 by respiration.

134. Buffers .. HCO3 22-26 mmol/lt (24mmol) Pka=6.1
H2CO3=(CO2 in forms dissolved)
pCO2=40
Solubility coeffeciant=0.3
pH=Pka+logHCO3/H2CO3
7.4=6.1+LOg24/1.2
7.4=6.1+LOg20
7.4=

136. Body buffers
Three mechanism: to regulate pH and acid base balance and maintain the blood pH (around 7.4)
1.blood buffers
2.respiratory mechanism
3.renal mechanism

138. EFFECTS OF ACID BASE DISTURBANCES
H+increased= acidosis,depression of C.N.S, Disorientation, death in coma.
H+decreased= alkalosis, overexcitability of C.N.S,convulsions.
First in peripheral Nerves than C.N.S
Sensory effects,Tingling(pins and needle sensation
Motor effects, muscle twitches, spasm
Extreme alkalosis- spasm of respiratory muscles, death

140. EFFECTS….. 2. CHANGES IN ENZYMES ACTIVITY
Altering shape and activity of protein molecule.
Some reactions are accelerated and some are depressed.

142. EFFECTS….. 3. CHANGES IN CELLULAR pH
Reduced contractility of actin and myosin in muscles.
CHANGES IN POTASSIUM LEVEL
H+ ions enters the cells for sodium and potassium.
H+ ions are eliminated more than potassium so hyperkalemia, cardic disfunction.

144. Blood buffers Bicarbonate buffer system: NaHCO/H2CO3
H2CO3 >H+ +HCO3
pH=pKa +log [salt]/[acid]
20:1 is the ratio
Alkali reserve : responsible for effective buffering of H+,generated in the body.

146. Blood buffers.
Bicarbonate buffers ;is index to understand the disturbances.
Phosphate buffers; this is important buffer intracellular .
Sodium di hydrogen phosphate and disodium hydrogen phosphate
Ratio of base to acid for phophate buffer is 4:1
Pk is 6.8

147. Body buffers
Three mechanism: to regulate pH and acid base balance and maintain the blood pH (around 7.4)
1.blood buffers
2.respiratory mechanism
3.renal mechanism

148. Physiological Buffers
Carbon Dioxide-Bicarbonate System; a major regulator of blood pH
Phosphate System; major regulator of cytosolic pH
[CO2] and [HCO3] are much higher than [PO4] in blood; the reverse is true in the cytosol, [PO4] >>> [HCO3]

149. Examples - Physiological Buffers
From Marks, Marks, Smith, Ch 4

150. From Marks, Marks, Smith, Ch 4

151. pH Titration Curves
From Lehninger, 2nd ed., Ch 4

152. Blood Bicarbonate and Metabolic Acidosis
The bicarbonate blood buffer in a normal adult
maintains the blood pH at about If the blood
pH drops below 7.35, the condition is referred to
as an ACIDOSIS. A prolonged blood pH below
7.0 can lead to death. Clinically for an acidosis,
the acid-base parameters (pH, [HCO3- ], [CO2] )
of the patients blood should be monitored. The
normal values for these are pH = 7.40;
[HCO3- ] = 24 mM; [CO2] = 1.2 mM.

153. Sample Problem – Metabolic Acidosis
The blood values of a patient were pH = and [CO2] = 1.1 mM. What is the patient’s blood [HCO3-] and how much of the normal [HCO3-] has been used in buffering the acid causing the condition?
The pK’ for [HCO3-]/[CO2] = 6.10

154. Solution Substitute into Henderson-Hasselbalch equation:
7.03 = log [HCO3-]/1.1 mM, or
0.93 = log [HCO3-]/1.1 mM
The anti-log of 0.93 = 8.5, thus:
8.5 = [HCO3-]/1.1 mM, or [HCO3-] = 9.4 mM
Since normal [HCO3-] equals 24 mM, there was a decrease of 14.6 mmol of [HCO3- per liter of blood in this patient. This would be approaching the point where, if left untreated, the HCO3- buffering capacity would be no longer effective in this patient.