Chapter 2.pdf

Chapter 2 Water 1 Outline 1.Function of Water 2.Distribution of Water in the Body 3.Physical and chemical properties of water 4. Ionization of Water, Weak Acids, and Weak Bases 1. Function of Water Sources of water 20% of water is provided by food such as soups, yogurts, fruit...

Chapter 2 Water 1 Outline 1.Function of Water 2.Distribution of Water in the Body 3.Physical and chemical properties of water 4. Ionization of Water, Weak Acids, and Weak Bases 1. Function of Water Sources of water 20% of water is provided by food such as soups, yogurts, fruit and vegetables. The other 80% is provided by drinks such as water, milk and juice. Water is a good choice of drink because it hydrates without providing energy. 1. Function of Water Our bodies lose water all the time, when we go to the toilet, from sweat and also through respiration. We need to replace this water by drinking regularly to prevent dehydration. Even mild dehydration can lead to headaches, irritability and loss of concentration. Did you know? Humans can survive for a few weeks without food, but they can only survive for a much shorter time without fluids.  2. Distribution of Water in the Body Function of water in human body systems ▪ Water is the most abundant substance in living systems, making up 70% or more of the weight of most organisms. ▪ Water is an essential material in biological reaction especially metabolism. https://www.fsis.usda.gov/food-safety/safe-food-handling-and-preparation/food-safety-basics/water-meat-poultry  2. Distribution of Water in the Body Fluid compartments in the body is paramount for the maintenance of health, function, and survival. For the average 70 kg man, 60% of the total body weight is comprised of water, equaling 42L.  2. Distribution of Water in the Body Water is essential substance for human survival. Water is the most abundant component of the human body, accounting for 60 to 70% of total body weight. This percentage of water in human being is required to be maintained by water as a foodstuff. Water balance in healthy adult subject  2. Distribution of Water in the Body Source of water: The body has three sources of water. Besides drinking water, the following are the sources of water. Fruits and vegetables contain 80-90 percent water. Milk contain 80-88 percent. Meat contains 40-75 percent Flour, cracks and bread contain 5-35 percent of water. Major functions of water Carrier of Food Nutrients: most nutrient in soluble form in water is carried from intestines to tissues through blood. Constituent of Liquid: Water is the major constituent of all liquids of body as blood, urine, sweat, lymph. Regulate body temperature: Water helps to regulate and control body temperature. Safety/Security of Delicate Organs: Water is around lungs, heart, brain which protects them from outer injury. Thus provide security to these organs and thereby to human being.  3. Physical and chemical properties of water ▪ The "universal solvent" and most abundant surface on Earth is water (H20). Water molecules are extremely polar and form hydrogen bonds. ▪ Water has five main properties: high polarity, high specific heat, high heat of vaporization, low solid density, and attraction to other polar molecules.  1. Physical and chemical properties of water In ice, each water molecule forms four hydrogen bonds, the maximum possible for a water molecule, creating a regular crystal lattice. This crystal lattice structure makes ice less dense than liquid water, and thus ice floats on liquid water. By contrast, in liquid water at room temperature and atmospheric pressure, each water molecule hydrogen-bonds with an average of 3.4 other water molecules.  1. Physical and chemical properties of water ▪ Polar biomolecules dissolve readily in water because they can replace water-water interactions with more energetically favorable water-solute interactions. ▪ In aqueous solutions, nonpolar molecules tend to cluster together. 12  1. Physical and chemical properties of water Water Forms Hydrogen Bonds with Polar Solutes Common hydrogen bonds in biological systems. The hydrogen acceptor is usually oxygen or nitrogen; the hydrogen donor is another electronegative atom. 13  1. Physical and chemical properties of water ▪ Hydrogen bonds between water molecules provide the cohesive forces that make water a liquid at room temperature and that favor the extreme ordering of molecules that is typical of crystalline water (ice). The difference in electronegativity between the oxygen and It has a bent molecular geometry with the hydrogens causes the oxygen to have a partial negative charge oxygen having two lone pairs of electrons. and the hydrogen to have a partial positive charge. Water has a higher melting point, boiling point, and heat of vaporization than most other common solvents. Why Group Activity Important notes 1. Entropy Increases as Crystalline Substances Dissolve. Explain why? What is entropy? 2. Nonpolar Gases Are Poorly Soluble in Water Explain why? What is Non-polar Gases? 3. Nonpolar Compounds Force Energetically Unfavorable Changes in the Structure of Water How the structure of water change?  3. Ionization of Water, Weak Acids, and Weak Bases ▪ Water can be explained in terms of the uncharged Pure Water Is Slightly Ionized H2O molecule, the small degree of ionization of water to hydrogen ions (H+) and hydroxide ions ▪ Like all reversible reactions, the ionization of (OH-). water can be described by an equilibrium Autoionization of water Reversible ionization constant. When weak acids are dissolved in water, they contribute H+ by ionizing; weak bases consume H+ by becoming protonated. The ionization of water can be measured by its electrical conductivity; pure water carries electrical current as H3O+ 19  3. Ionization of Water, Weak Acids, and Weak Bases As a result of the high ionic mobility of H+, acid-base reactions in aqueous solutions are exceptionally fast. The equilibrium constant Keq can be defined in terms of the concentrations of reactants (A and B) and products (C and D) at equilibrium: The equilibrium constant of a chemical reaction (usually denoted by the symbol K) provides insight into the relationship between the products and reactants when a chemical reaction reaches equilibrium. The pH Scale Designates the H+ and OH Concentration The total hydrogen ion concentration from all sources is experimentally measurable and is expressed as the pH of the solution. Kw 21 Calculate pH value of solution. 22 The pH of some aqueous fluids. 23  Weak Acids and Bases ▪ Hydrochloric, sulfuric, and nitric acids, commonly called strong acids, are completely ionized in dilute aqueous solutions; the strong bases NaOH and KOH are also completely ionized. ▪ Of more interest to biochemists is the behavior of weak acids and bases—those not completely ionized when dissolved in water. These are ubiquitous in biological systems and play important roles in metabolism and its regulation. Weak Acids Weak Bases Find out what the different between Weak acid and bases Weak Acids and Bases Have Characteristic Dissociation Constants 25  Titration Curves Reveal the pKa of Weak Acids The titration curve of acetic acid. After addition of each increment of NaOH to the acetic acid solution, the pH of the mixture is measured. This value is plotted against the amount of NaOH added, expressed as a fraction of the total NaOH required to convert all the acetic acid (CH3COOH) to its deprotonated form, acetate (CH3COO–). 26 Titration is used to determine the amount of an acid in a given solution. A measured volume of the acid is titrated with a solution of a strong base, usually sodium hydroxide (NaOH). 28