Lecture 1: Physico-Chemical Chemistry PDF

‫ب ِّزد ِّني ِّعل ًما‬ ‫ُ‬ ‫َوقل َّر ِّ‬ ‫سورة طه ‪ -‬اآلية ‪114‬‬ Physico-chemical Chemistry Directed by Pro.Dr/ Maathir kamel  Solutions Definition: Solutions are substances dissolved in solvents e.g., water. Expressions of concentrati...

‫ب ِّزد ِّني ِّعل ًما‬ ‫ُ‬ ‫َوقل َّر ِّ‬ ‫سورة طه ‪ -‬اآلية ‪114‬‬ Physico-chemical Chemistry Directed by Pro.Dr/ Maathir kamel  Solutions Definition: Solutions are substances dissolved in solvents e.g., water. Expressions of concentration: Concentration of a solution is expressed in molarity or normality (1) Molar Solution (M): Molar solution contains one mole of a substance in grams dissolved in one liter of the solvent. For example: - Molar solutions of NaOH contain 40 grams / liter. - Molar solutions of HCL contain 36.5 grams / liter. - Molar solutions of H2SO4 contain 98 grams / liter. (2) Normal solutions (N): Normal solution contains one mole of a substance in grams divided by an equivalence factor, dissolved in one liter of the solvent. For example: - Normal solution of H2SO4= 98/2= 49 gm H2SO4 dissolved in one liter of H2O - Normal & molar solutions of NaOH are equal = 40 grams / liter. - Normal & molar solutions of HCL are equal = 36.5 grams / liter. (3) Molal solution: Molal solution contains one mole of a substance in grams dissolved in 1000 g of solvent.  Osmolarity and Osmolality ❑Osmolarity define the relationship between concentration of substance and volume of solvent as the volume differs with change in temperature, so osmolarity depends on temperature. ❑Osmolality defines the relationship between concentrations of substance and mass of solvent (concentration of substance/kg water), so osmolality does not depend on temperature.  PH PH is defined as the negative logarithm of hydrogen ion concentration to base 10. pH = - Log [H+] = - Log 10-7= - (-7) = 7 Low pH values correspond to high concentration of H+ and high pH values correspond to low concentrations of H+. * Maintenance of the extracellular fluid between pH 7.35 and 7.45 is essential for health. Thus, A neutral solution has pH = 7 An acidic solution has pH less than 7 An alkaline solution has pH more than 7  Acids, Bases and Alkalies Acids: They are proton or hydrogen donors. 2 types exist: 1) Strong acids e.g., HCl, H2SO4, which completely dissociate even in strongly acidic solutions (at low pH). 2) Weak acids e.g., acetic acid which dissociate only partially in acidic solutions. Bases: They are proton or hydrogen acceptors. There are 2 types: 1) Strong bases e.g., KOH, NaOH which are dissociated at high pH. 2) Weak bases e.g., Fe[OH]3 which dissociate only partially at high pH.  BUFFERS Buffers are solutions, which resist a change in pH following the addition of strong acid or strong base. Buffers are composed of mixtures of either: (1)A weak acid and its salt with a strong base e.g., carbonic acid + bicarbonate. This is the most common in physiologic systems. (2)A weak base and its salt with strong acid e.g., ammonium hydroxide + ammonium chloride. Mechanism of action of buffers: On addition of a strong acid for example to bicarbonate buffer, a neutral salt and weakly dissociated acid are produced which have no effect on pH. HCL + NaHCO3 NaCL + H2CO3 Neutral weak Salt acid  On addition of a strong base e.g., NaOH to bicarbonate buffer, weakly dissociated base and water are produced which have no effect on pH. NaOH + H2CO3 NaHCO3 + H2O Weakly dissociated base Types of buffers: (A) Non-physiologic buffers: These are used in biochemical experimentation and include TRIS and HEPES. (B) Physiologic buffers: Any acid or base formed inside the body should be rapidly buffered since enzymes, which control metabolic reactions, are very sensitive to change in pH. The physiologic buffer systems present in various tissues and body fluids function to keep the pH stable For example, blood pH must be maintained within a range of 7.35 - 7.45. Physiologic buffers include the following: (1) Bicarbonate buffer (HCO3): It is formed of carbonic acid and sodium or potassium bicarbonate. It is the most efficient for buffering of all acids added to the blood. The ratio of bicarbonate salt to carbonic acid is 20/1 at pH 7.4.  (2) Phosphate buffer: This is the chief buffer in urine. The ratio of base to acid is 4/1. (3) Protein buffer: The protein buffers include the plasma proteins: albumin, globulins and fibrinogen in the plasma and the hemoglobin and oxyhemoglobin systems in the red blood cells. The hemoglobin and oxyhemoglobin systems are responsible for the buffering of most of the CO2 added to the blood by tissues.  In the plasma, the base is Na while in the red cells, it is mainly K. The buffer systems are so efficient that they keep the blood pH within a very limited range (7.35 - 7.45), in spite of continuous addition of acids e.g., sulfuric, phosphoric, uric, acetic, lactic, amino and fatty acids. These buffers present either in plasma &extracellular tissue or inside RBCS A.Plasma buffers include: 1. Bicarbonate buffer (NaHCO3/ H2CO3) 2. Phosphate buffer (Na2HPO4/NaH2PO4) 3. Plasma proteins (H protein/Na proteinate) A.RBCS buffers include: 1. Bicarbonate buffer (KHCO3/ H2CO3) 2. Hemoglobin buffer (H-Hb / K-Hb) 3. Oxyhemoglobin buffer (H-HbO2 / K-HbO2)  ACIDOSIS Acidosis is a condition in which the blood pH tends to decrease. It may be divided into respiratory acidosis or metabolic acidosis. (A) Respiratory acidosis: In respiratory acidosis, the lungs fail to excrete CO2 at the proper rate causing increased blood CO2 and hence blood H2CO3. Respiratory acidosis is caused by: a. Obstructive lung disease e.g., bronchial asthma and emphysema. b. Depression of the respiratory center as in morphine poisoning.  In, respiratory acidosis, the blood ratio of HCO3- /H2CO3 is decreased, causing decreased blood pH. This stimulates the kidney to reabsorb more HCO3-till the ratio HCO3-/H2CO3 returns to 20/1. (B) Metabolic acidosis: In metabolic acidosis, the blood HCO3- tends to decrease due to one of the following causes: 1) Increased production of acids as in muscular exercise (lactic acid), ketosis (ketone bodies), high protein diet (sulfuric, phosphoric, and uric acids). 2) Failure of excretion of acids as in kidney failure 3) Increased loss of bases as in diarrhea (loss of pancreatic and intestinal juices)  In metabolic acidosis, decreased blood ratio of HCO3- /H2CO3 lowers the blood PH. This stimulates the respiration causing loss of CO2 through the lungs leading to decreased blood H2CO3 until the ratio HCO3- /H2CO3 reaches 20/1 and blood pH returns to 7.4.  ALKALOSIS Alkalosis is a condition in which the blood pH tends to increase. It may be respiratory alkalosis or metabolic alkalosis. (A) Respiratory alkalosis: In respiratory alkalosis, there is increased loss of CO2 through the lungs causing decreased blood H2CO3. This occurs in cases of hyperventilation due to fevers, salicylate poisoning, high altitudes and hysteria.  In respiratory alkalosis, increased blood pH inhibits the renal tubular reabsorption of HCO3-, decreasing the blood, HCO3- until the ratio HCO3-/H2CO3 becomes 20/1 and blood pH returns to 7.4, but the alkali reserve is decreased. (B) Metabolic alkalosis: In metabolic alkalosis, there is increased blood HCO3-, caused by: (1)Increased loss of acids As in vomiting (loss of gastric HCL) after major operation, hypokalemia and Cushing’s syndrome. (1)Increased absorption of bases as in cases of: High vegetable and fruit diet which are rich in sodium and potassium citrates. These are converted to bicarbonates in the body. Administration of sodium and potassium citrates and bicarbonates for treatment of hyperacidity and peptic ulcer.  In metabolic alkalosis, increased blood pH inhibits the respiration, causing decreased loss of CO2 through the lungs, increased blood H2CO3 until the ratio HCO3- /H2CO3 becomes 20/1, and blood PH returns to 7.4 but the alkali reserve is increased.