Chemical Buffers
Chemical Buffers
Chemical Buffers
HCl
donor-K1
H2O
acceptor-B2
acceptor-B1
NH3 + H2O
+
donor-K2
donor-K1 NH4+(aq)
acceptor-B2
+ +
+OH- (aq) -
H 3O + +
A-
Weak acids dont dissociate completely and the equilibrium is moved toward undissociated acid. Concentrations of H3O+ and (A-) are low. CH3COOH + H2O CH3COO- + H3O+ HA + H2O H 3O + + AKeq = [H3O+][A-] [HA][H2O] Ka = Keq[H2O] = [H3O+][A-] [HA]
H 2 O + H2 O
+ acid (H+)
+ base (OH-)
Basic solution
Acidic
0
Basic
1 2 3 4 5 6 7 8 9 10 11 12 13 14
pH of Blood
pH of blood is 7,4, [H+] = 4 x 10-8 = 40 nmol H+ / L of blood Allowed variation of pH of blood is pH 0,05 or concentration of H+ 5 nmol / L blood
pH > 7,8
pH = 7,3 [H+] = 5 x 10-8 = 50 nmol H+ / L of blood Decreasing of pH for 0,1 unit, the concentration of [H+] increases for 25%. pH = 7,1 [H+] = 8 x 10-8 = 80 nmol H+ / L of blood Decreasing of pH for 0,3 unit, the concentration of [H+] increases twice.
CHEMICAL BUFFERS
Buffers are mixtures of weak acids and their conjugated
strong bases (salts) or mixtures of weak bases and their conjugated strong acids.
Chemical buffers confer resistance to a change in the pH of a solution when hydrogen ions (protons) or hydroxide ions are added or removed.
CHEMICAL BUFFERS
BUFFER: HA (weak acid)/A- (strong conjugated base)
- If [HA] = [A-], then pH = pKa -pH of buffer does not change with dilution of solutions - Efficiency of buffer:
pH pKa log 10 pKa 1 1 pH pKa log
[A ] pH pK a log [HA]
1 pKa 1 10
pH = pKa 1
MECHANISM OF BUFFERS ACTION Buffer: HA/AHA H+ + A- NaA Na+ + A[A ] pH pK a log [HA]
HA + OH H2O + A
Henderson-Hasselbach equilibrium
A-
AHA
HA AHA A-
A-
H+
HA
A-
BLOOD BUFFERS
Blood buffers are:
Bicarbonate buffer, H2CO3 HCO3-, It is the most important inorganic blood buffer. It represents 5% of buffer systems in blood. Phosphate buffer, H2PO4- HPO42-; It represents 1% of buffer capacity of blood.
Proteins buffer, proteine proteinate, It represents 93% of buffer capacity of blood, 80% of it corresponds to hemoglobin and 13% corresponds to the rest of proteins of blood serum.
Bicarbonate buffer H2CO3 /HCO3The carbonic acid-hydrogen carbonate ion buffer works throughout the body to maintain the pH of blood plasma close to 7.40. The body maintains the buffer by eliminating either the acid (carbonic acid) or the base (hydrogen carbonate ions).
CO2(aq) + H2O(l)
CO2(aq) + H2O(l) CO2(g) CO2(aq)
H2CO3 (aq)
HCO3-(aq) +H+(aq)
HCO3-(aq) + H+(aq)
MECANISM OF ACTION:
HCO3-(aq) + H+ (aq) H2CO3(aq) + OH-(aq) H2CO3 (aq) H2O(l) + HCO3-(aq) CO2(aq) + H2O(l)
Bicarbonate buffer
H2CO3 /HCO3-
Changes in carbonic acid concentration can be effected within seconds through increased or decreased respiration.
Changes in hydrogen carbonate ion concentration, however, require hours through the relatively slow elimination through the kidneys
Respiratory Alkalosis
Respiratory alkalosis is a condition in which the pH of the blood is above
normal (pH > 7.4). The increase in pH value is often caused by hyperventilation (excessively deep breathing). When a person hyperventilates they exhale more carbon dioxide than normal. As a result the carbon dioxide concentration in the blood is reduced and the bicarbonate/carbonic acid equilibrium shifts to the left. The corresponding drop in H3O+ concentration causes an increase in pH.
2 H2O + CO2
H2CO3 + H2O
H3O+ + HCO3-
breathe into a paper bag. In doing so, they rebreathe some of expelled carbon dioxide, and blood carbon dioxide levels return to normal.
Respiratory Acidosis
Respiratory acidosis is caused by the reverse process (pH< 7.4). A hypo ventilating (excessively shallow breathing) person does not expel enough carbon dioxide and has elevated blood carbon dioxide levels. This causes the equilibrium to shift to the right, the H3O+ concentration increases and pH drops. 2 H2O + CO2 H2CO3 + H2O H3O+ + HCO3-
Metabolic Acidosis
Metabolic acidosis is a condition of low blood pH resulting from nonrespiratory causes. Those processes that remove bases from the body or produce acids may cause metabolic acidosis. A common example is overexertion. When a person overly exerts themselves an insufficient supply of oxygen to the active muscles results in the production of large amounts of lactic acid. If the amount of lactic acid produced exceeds the buffering capacity of the blood, the blood pH will be lowered.
Metabolic Alkalosis
Any condition in which a high blood pH is present due to non-respiratory
causes is called metabolic alkalosis. In general, those processes that remove acids from the body or produce bases may cause metabolic alkalosis. One example is the overuse of diuretics. Diuretics increase the amount of urine excreted from the body and, if the urine carries with it large amounts of acids, the blood pH will be increased.
performed. Bicarbonate (basic) solutions are used for patients experiencing extreme acidosis and ammonium chloride (acidic) solutions are used for those with extreme alkalosis.
PHOSPHATE BUFFER H2PO4- /HPO42(KH2PO4 i K2HPO4 in cells) (NaH2PO4 i Na2HPO4 in intercellular solutions) MECANISM OF ACTION: HPO42- + H+ H2PO4- + OHH2PO4H2O + HPO42-
Phosphate buffer takes place in homeostasis of HCO3- in kidneys H2PO4- + HCO3H2CO3 + HPO42H2O +CO2 CO2 (aq) + H2O
CA
HCO3- + H+
PHOSPHATE BUFFER H2PO4- /HPO42Phosphate buffer takes place in homeostasis of HCO3- in kidneys H2PO4- + HCO3H2CO3 + HPO42CO2 (aq) + H2O
CA
H2O +CO2
cells
HCO3- + H+
kidneys
H2PO4- + Na+
+ OHH2PO4+ H+
Blood circulation HPO42-
urine
HPO42- + 2Na+
Pr COOH Pr COO- + H+; pH = pK(Pr COOH) + log [Pr COO-] / [Pr COOH];
Henderson-Hasselbach equilibria obtained from dissocitation of acidic proteins
NH3
Pr R
COOH
OH H
+
NH3
Pr R
COO-
OH H
+
NH2
Pr R
COO-
BLOOD GASSES
1. Blood rich in carbon dioxide is pumped from the heart into the lungs through the pulmonary arteries. (Arteries are blood vessels carrying blood away from the heart; veins are blood vessels carrying blood to the heart.) 2. In the lungs, CO2 in the blood is exchanged for O2. 3. The oxygen-rich blood is carried back to the heart through the pulmonary veins. 4. This oxygen-rich blood is then pumped from the heart to the many tissues and organs of the body, through the systemic arteries. 5. In the tissues, the arteries narrow to tiny capillaries. Here, O2 in the blood is exchanged for CO2. 6. The capillaries widen into the systemic veins, which carry the carbon-dioxide-rich blood back to the heart.
from air
O2 HbO2-
H+
in erythrocytes
H+
Just formed
HCO3-
CO2
H2 O
DEOXIGANATION
In the presence of CO2 and H+ (e.g., in the muscles), charged groups are formed on the amino acid residues lining the subunit interface. These charged groups are held together by ionic interactions, forming "salt bridges" between the two subunits, and stabilizing the deoxygenated form of hemoglobin. When blood passes through the alveolar capillaries of the lungs, CO2 and H+ are removed from the hemoglobin, and the oxygenated configuration is favored (right).
H2 O
HCO3-
H+
in erythrocytes
H+
HbO2-
HHb
in erythrocytes
O2
CO2(aq)
In tissues
HHb(aq)
Hb-CO2(aq)
H+(aq)
carbamino-hemoglobin in erythrocytes