Water, Acids, Bases, and Buffers PDF

Water, Acids, Bases and Buffers Sopio Dzneladze 1 Biochemistry is the study of the chemical reactions that take place inside organisms. It combines elements from both biology and chemistry. Sopio Dzneladze 2 Water Solvent of life; Dissolves and transp...

Water, Acids, Bases and Buffers Sopio Dzneladze 1 Biochemistry is the study of the chemical reactions that take place inside organisms. It combines elements from both biology and chemistry. Sopio Dzneladze 2 Water Solvent of life; Dissolves and transport compounds; Provides medium for movement of molecules into and throughout cellular compartment; Separates charged molecules; Dissipates heat; Participate in chemical reactions. Sopio Dzneladze 3 formula Sopio Dzneladze 4 A water molecule is formed when two atoms of hydrogen bond covalently with an atom of oxygen. In a covalent bond electrons are shared between atoms. Sopio Dzneladze 5 A molecule, with electrical charge distributed asymmetrically about its structure is a dipole. Sopio Dzneladze 6  Covalent bond, in chemistry, the interatomic linkage that results from the sharing of an electron pair between two atoms. Sopio Dzneladze 7 The hydrogen bond in water is a dynamic attraction between neighboring water molecules involving one hydrogen atom located between the two oxygen atoms. Sopio Dzneladze 8  Covalent bond is a primary chemical bond formed by the sharing of electron pairs. Covalent bonds are strong bonds with greater bond energy. Hydrogen bond is a weak electrostatic attraction between the hydrogen and an electronegative atom due to their difference in electro negativity. Sopio Dzneladze 9 Water as a solvent Water molecules have a polar arrangement of the oxygen and hydrogen atoms—one side (hydrogen) has a positive electrical charge and the other side (oxygen) has a negative charge. This allows the water molecule to become attracted to many other different types of molecules. Sopio Dzneladze 10 Water can become so heavily attracted to a different molecule, like salt (NaCl), that it can disrupt the attractive forces that hold the sodium and chloride in the salt molecule together and, thus, dissolve it. Sopio Dzneladze 11  Hydrogen bonds are strong enough to dissolve polar molecules in water and to separate charges; Electonegativity – measures the tendency of an atom to attract a shared pair of electrons. Sopio Dzneladze 12  Water and thermal regulation The structure of water allows it to resist temperature change Sopio Dzneladze 13 Electrolytes Electrolytes are minerals in your body that have an electric charge. They are in your blood, urine, tissues, and other body fluids. Electrolytes are important because they help. Balance the amount of water in your body. Balance your body's acid/base level. Sopio Dzneladze 14 Sopio Dzneladze 15 Sopio Dzneladze 16 Sopio Dzneladze 17 Sopio Dzneladze 18 Sopio Dzneladze 19 Sopio Dzneladze 20  The pH of water pH is the negative log of the hydrogen ion concentration expressed in mole per liter (mol/l). pH=-log[H+] pH=-log10-7=-(-7)=7 (“p” is negative log) Sopio Dzneladze 21  Strong and weak acids Inorganic acids such as sulfuric acid and hydrochloric acid are strong acids that dissociate completely in solution Organic acids, containing carboxylic acid groups are weak acids that dissociated to only limited extent in water. Acids are compounds that donate a Hydrogen ion to a solution (H+); Bases are compounds (such as a OH- ion) that accept hydrogen ion. Sopio Dzneladze 22 The quantitative relationship between the pH of the solution and concentration of a weak acid (HA) and its conjugate base (A-) is described as Henderson - Hasselbalch equation. Sopio Dzneladze  Neutral pH of water Dissociation constant of water Kd expresses the relationship between the hydrogen ion concentration, the hydroxide ion concentration, and the concentration of water at equilibrium: Sopio Dzneladze 24  Henderson - Hasselbalch equation Describes the behavior of weak acids and buffers; Describes the derivation of pH as a measure of acidity in biological and chemical systems; For estimating the pH of a buffer solution and finding the equilibrium pH in acid-base reaction. Sopio Dzneladze  Larger Ka – stronger the acid; Smaller Ka – weaker the acid, the less acid has dissociated; Smaller pKa – stronger acid; Sopio Dzneladze Sopio Dzneladze  The pKa value is one method used to indicate the strength of an acid. pKa is the negative log of the acid dissociation constant or Ka value. A lower pKa value indicates a stronger acid. That is, the lower value indicates the acid more fully dissociates in water. Sopio Dzneladze Sopio Dzneladze 29  Acidosis - A process causing increased acidity in the blood and other body tissues (increased hydrogen ion concentration); Alkalosis - is a condition in which the body fluids have excess base (alkali); Your blood has a normal pH range of 7.35 to 7.45. This means that blood is naturally slightly alkaline or basic. In comparison, your stomach acid has a pH of around 1.5 to 3.5. This makes it acidic. Sopio Dzneladze 30  buffers Buffers, which consist of a weak acid and its conjugate base cause a solution to resist changes in pH when hydrogen ions or hydroxide are added. Sopio Dzneladze 31 Sopio Dzneladze 32 Sopio Dzneladze 33  Maximum amount of either strong acid or strong base that can be added before a significant change in the pH will occur is a buffer capacity. The maximum buffering capacity occurs at a pH equal to the pKa; If the amount of HA and A are equal, the pH is equal to the pKa; Sopio Dzneladze  The major buffer systems in the body Bicarbonate-carbonic acid buffer system, which operates principally in ECF; The hemoglobin buffer system in RBC; The phosphate buffer system in all types of cells; Protein buffer system of cells and plasma. Sopio Dzneladze 35  Metabolic acids and buffers Metabolism – a term that is used to describe all chemical reactions involved in maintaining the living state of the cells and the organism; Metabolic activity produces roughly 22000 mEq of acids per day; pH of blood is normally maintained between 7.36-7.44. Sopio Dzneladze 36  Bicarbonate buffer system (ECF) CO2+H2O H2CO3 HCO3-+H+ H2CO3 + OH- HCO3 + H2O HCO3 + H+ H2CO3 Enzyme is : carbonic anhydrase Carbonic acid is both: The major acid produced by the body; Its own buffer. Sopio Dzneladze 37  Bicarbonate and hemoglobin in RBC Bicarbonate buffer system (in ECF) and Hb (in RBC) cooperate in buffering the blood and transporting CO2 to the lungs. HbO2 / HHb HHb / KHb Strong acid/ weak acid weak acid/weak base KHb + H2CO3 KHCO3 + HHb HHb + OH- H2O +Hb Sopio Dzneladze 38  Phosphate buffer system in ICF H2PO4- /HPO42- H2PO4- + OH- HPO42- + H2O HPO4- + H+ H2PO4- Sopio Dzneladze 39 Protein buffer system Sopio Dzneladze 40  Urinary hydrogen, ammonium and phosphate ions Nonvolatile acids from metabolism cannot be excreted as expired CO2 and its excreted in the urine. pH of urine is 5,5 – 7,0 Phosphate and ammonium ions, uric acid, dicarboxilic acid, citric acid, sulfuric acid. Sopio Dzneladze 41 Buffering system of a body Sopio Dzneladze 42  References: Mark’s Medical Biochemistry: pp. 42-50. Sopio Dzneladze 43