Solutions. Acid–base equilibrium in biological systems

Сентябрь 9, 2022

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Solutions. Acid–base equilibrium in biological systems

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2. Plan 0. Solutions and their colligative properties 1. The theory of electrolytic dissociation. Dissociation of bases,
19. Theory of electrolytic dissociation (Arrhenius’ theory). Protolytic theory (Bronsted – Lowry’ theory). Electronic theory (Lewis’ theory).
20. The theory of electrolytic dissociation
22. Electrolytic dissociation – process of decomposition of solutes in the solvent into ions.
23. 1) Substances dissociating in solutions or melts into positively charged Cat+(cations) and negatively charged An- (anions).
24. Dissociation of bases, acides and salts in water solutions
25. Acides are compounds dissociating in aqueous solutions with the formation of positive ions of one species
26. Strong and weak electrolytes
27. Degree of dissociation α Ni - the number of molecules, dissociating into ions; Ntot – the
29. Strong electrolytes Majority of salts. Some acids (HCl, HBr, HI, HNO3, HClO4, H2SO4). Alkalis (LiOH, NaOH,
30. Weak electrolytes Majority of acids and bases (H2S, H2CO3, Al(OH)3, NH4OH).
31. The dissociation of weak electrolytes is a reversible process CatAn Cat+ + An-
32. The equilibrium constant K is called the dissociation (ionization) constant
33. Ostwald dilution law Because in solutions of weak electrolytes, degree of dissociation of a very small
34. Acidity and basicity constants The dissociation constants of acids and bases, respectively called acidity constants (KA)
36. Dissociation of water H2O H+ + OH-
37. Kw is constant, ion product of water.
38. Hydrogen ion exponent pH= -lg [H+]
39. pH Measurement indicators pH - meters
41. Protolytic theory Danish physicist and chemist Johannes Brønsted and the English chemist Thomas Lowry in 1928-1929
42. Base - a substance (particle) that can attach proton (i.e. base - proton acceptor). Acid- a
43. Salt - the reaction product of acid and base Example: Conjugated acid Conjugated base By this
44. The homeostasis. The importancy of pH maintenance in human body The human body has mechanisms of
45. The constancy of hydrogen ions concentration is one of important constant of internal medium of organism,
46. pH values of different biological fluids and tissues of the human body
47. The concept of buffer solutions Buffer solutions are solutions that resist change in hydrogen ion and
49. The resistive action is the result of the equilibrium between the weak acid (HA) and its
50. Henderson-Hasselbah equation
51. Buffer capacity Buffer capacity (B) - the number of moles of equivalents of strong acid or
52. Buffer capacity Buffer capacity is maximal at a ratio of acid salt 1:1 => pH =
53. The relative contribution% buffer systems in the blood to maintain homeostasis it protolytic Buffer systems plasma
54. Hydrocarbonate buffer system HCO3- +H+ H2CO3 H2CO3+OH- HCO3-+ H2O CO2+ H2O H2CO3
55. pKa1(H2CO3)=6.1 pH of a blood plasma = 7.4
56. Alkaline reserve HCO3-+ H+ H2CO3 CO2+ H2O
57. Phosphate buffer system HPO42-+H+ H2PO4- H2PO4-+OH- HPO42-+H2O
58. The mechanism of action of phosphate buffer: 1. acid addition 2 Na++HPO42–+H++Cl -→ NaH2PO4+Na++Cl - 2.
59. pKa(H2PO4-)=6.8 pH of a blood plasma = 7.4
60. Protein buffer systems The plasma proteins (albumins, globulins) are less important than the hemoglobin for maintenance
61. PROTEIN acid-base buffer system
62. Hemoglobin buffer system
64. Hemoglobin acid-base buffer system BLOOD
65. Binding of hydrogen cations imidazole groups of hemoglobin.
66. Hemoglobin buffer system HHb + O2 HHbO2 Hemoglobin is a weaker acid (pKa HHb = 8.2)
67. a) the hemoglobin buffer system: HHb H+ + Hb-; b) the buffer system formed by oxyhemoglobin:
68. In erythrocytes: HHbO2 HHb + O2 (1) HHbO2 H+ + HbO2- (2) HbO2- Hb- + O2
69. In vessels of tissues
71. In vessels of tissues CO2+ H2O H2CO3 HbO2-+ H2CO3 HHbO2 + HCO3- HHbO2 HHb + O2
72. In lungs
74. In lungs HHb + O2 HHbO2 HHbO2+ HCO3- HbO2-+ H2CO3 H2CO3 CO2+ H2O
75. Acidosis and alkalosis
77. Скачать презентацию

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Plan
0. Solutions and their colligative properties
1. The theory of electrolytic dissociation.

Dissociation of bases, acides and salts in water solutions.Strong and weak electrolytes
2. Protolytic theory.
3. Dissociation of water. Hydrogen ion exponent.
The homeostasis.
4. The importancy of pH maintenance in human body. 5. The concept of buffer solutions.
6. Hydrocarbonate buffer system
7. Phosphate buffer system
8. Protein buffer systems
9. Hemoglobin buffer system
10. Acidosis and alkalosis. Treatment of acidosis and alkalosis.

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Theory of electrolytic dissociation (Arrhenius’ theory).
Protolytic theory (Bronsted – Lowry’ theory).
Electronic

theory (Lewis’ theory).

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The theory of electrolytic dissociation

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Electrolytic dissociation –
process of decomposition
of solutes in the solvent

into ions.

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1) Substances dissociating in solutions or melts into positively charged Cat+(cations)

and negatively charged An- (anions). The latter include acids, bases and salts. 2) In electric field Cat+ move to cathode, An- move to anode. 3) Electrolytes decompose into ions in different degree. 4) Dissociation depend of: a) nature of electrolyte; b) nature of solvent; c) concentration; d) temperature.

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Dissociation of bases, acides and salts in water solutions

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Acides are compounds dissociating in aqueous solutions with the formation of

positive ions of one species – hydrogen ions. HCl→H+ + Cl- Bases are compounds dissociating in aqueous solutions with the formation of negative ions of one species – hydroxide ions OH-. Ca(OH)2→Ca2++ 2OH- Medium salts dissociate to form metal cations and anion of acid radical.

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Strong and weak electrolytes

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Degree of dissociation α
Ni - the number of molecules, dissociating

into ions;
Ntot – the total number of dissolved molecules.

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Strong electrolytes
Majority of salts.
Some acids (HCl, HBr, HI, HNO3, HClO4,

H2SO4).
Alkalis (LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2 , Sr(OH)2, Ba(OH)2)

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Weak electrolytes
Majority of acids and bases
(H2S, H2CO3, Al(OH)3, NH4OH).

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The dissociation of weak electrolytes is a reversible process
CatAn Cat+ +

An-

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The equilibrium constant K is called the dissociation (ionization) constant

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Ostwald dilution law
Because in solutions of weak electrolytes, degree of dissociation

of a very small quantity, 1-α = 1, then

Dissociation constant, Kd, and the degree of dissociation,
M is the molar concentration of the solution. Very often,
instead of the dissociation constants are in their common logarithms:

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Acidity and basicity constants
The dissociation constants of acids and bases, respectively

called acidity constants (KA) and major (KB).
Product constant acidity and basicity constants, with the acid conjugate base is the ion product of water:

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Dissociation of water
H2O H+ + OH-

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Kw is constant, ion product of water.

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Hydrogen ion exponent
pH= -lg [H+]

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pH Measurement
indicators
pH - meters

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Protolytic theory
Danish physicist and chemist Johannes Brønsted and the English chemist

Thomas Lowry in 1928-1929 was offered Protolytic (protonic) theory of acids and bases, according to which:

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Base - a substance (particle) that can attach proton (i.e. base

- proton acceptor).
Acid- a substance (particle) that can donate proton (i.e. acid – proton donor)
In the general form:

А-(acid); B-(base).
Such a system, consisting of acids and bases called protolytic conjugate pair of acid and base, offsetting or appropriate

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Salt - the reaction product of acid and base
Example:
Conjugated acid
Conjugated base
By

this theory, acids and bases may be both neutral molecules and ions (cations and anions).

Conjugated base

Conjugated acid

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The homeostasis. The importancy of pH maintenance in human body
The human

body has mechanisms of coordination of physiological and biochemical processes proceeding inside it and maintenance constancy of internal medium (optimal value of pH, levels of different substances, temperature, blood preassure). This coordination and mantanance are called homeostasis.

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The constancy of hydrogen ions concentration is one of important constant

of internal medium of organism, because:

1) Hydrogen ions have catalytic effect on many biochemical processes;
2)Enzymes and hormones exhibit biological activity only at a specific range of pH values;
3)Small changes of pH in blood and interstitial fluids affect the value of the osmotic pressure in this fluids.

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pH values of different biological fluids and tissues of the human

body

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The concept of buffer solutions
Buffer solutions are solutions that resist change

in hydrogen ion and the hydroxide ion concentration (and consequently pH) upon addition of small amounts of acid or base, or upon dilution.

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The resistive action is the result of the equilibrium between the

weak acid (HA) and its conjugate base (A−):
H+(aq) + A−(aq) → HA(aq)
OH-(aq) + HA(aq) → A−(aq) +H2O(l)

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Henderson-Hasselbah equation

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Buffer capacity
Buffer capacity (B) - the number of moles of equivalents

of strong acid or alkali to be added to 1 liter of buffer solution to shift the pH unit
Вac.=
Вbas.=

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Buffer capacity
Buffer capacity is maximal at a ratio of acid salt

1:1 => pH = pK.
Good – at [pK+0.5, pK-0.5]
Sufficient – at [pK+1, pK-1]
The higher the concentration of the solution, the greater the buffer capacity. The concentration of acid and salt in the buffer solutions usually about 0.05-0.20 M.

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The relative contribution% buffer systems in the blood to maintain

homeostasis it protolytic
Buffer systems plasma
Hydrogen carbonate 35%
Protein 7%
Hydrogen phosphate 1%
TOTAL 43%
Buffer systems erythrocytes
Hemoglobin 35%
Hydrogen carbonate 18%
Hydrogen phosphate 4%

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Hydrocarbonate buffer system
HCO3- +H+ H2CO3
H2CO3+OH- HCO3-+ H2O
CO2+ H2O H2CO3

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pKa1(H2CO3)=6.1
pH of a blood plasma = 7.4

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Alkaline reserve
HCO3-+ H+ H2CO3 CO2+ H2O

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Phosphate buffer system
HPO42-+H+ H2PO4-
H2PO4-+OH- HPO42-+H2O

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The mechanism of action of phosphate buffer:
1. acid addition
2 Na++HPO42–+H++Cl -→

NaH2PO4+Na++Cl -
2. adding alkali :
NaH2PO4 + NaOH → Na2HPO4 + H2O
Excess hydrogen phosphate monobasic and removed through the kidneys. Full recovery of relations in the buffer occurs only 2-3 days.

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pKa(H2PO4-)=6.8
pH of a blood plasma = 7.4

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Protein buffer systems
The plasma proteins (albumins, globulins) are less important than

the hemoglobin for maintenance of pH.

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PROTEIN acid-base buffer system

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Hemoglobin buffer system

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Hemoglobin acid-base buffer system BLOOD

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Binding of hydrogen cations imidazole groups of hemoglobin.

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Hemoglobin buffer system
HHb + O2 HHbO2
Hemoglobin is a weaker acid

(pKa HHb = 8.2) than oxyhemoglobin (pKa HHbO2 = 6.95). Therefore Hb- ions being anions of weaker acid are capable stronger to bind H+ ions than HbO2- ions.
Undissociated molecules HHbO2 lose O2 easier than the ions HbO2-

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