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Chapter 2

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BIOL 2000

CHAPTER 2 – WATER & CARBON : THE CHEMICAL BASIS OF LIFE LEARN HOW TO MAKE A CHEMICAL SOLUTION – 15 POINTS ON THE FIRST TEST MOLES, MOLECULAR WEIGHT, MOLARITY 23 mole = 6.022 X 10 molecular weight – sum of all the mass numbers of all the atoms in a molecule, grams/mol molarity – number of moles in an atom, mol SOLUTION CHEMISTRY solutions – composed of solutes (dissolved) in solvents (liquid) ex. NaCl (solvent) in water (universal solvent) Find MW of 5M NaCl MW NaCl = MW Na + MW Cl 23 + 35.5 58.5 g/mol 5M NaCl g = MxLxMW = mol/L x L x g/mol (5M0 (1L) (58.5 g/mol) = 292.5 g need to be dissolved in 1 L2H O to make a 5M NaCl solution to dilute a solution –initial inifinal final (what you want / what you have) (final V) = volume needed from original solution ex. make 250 mL of a 2M NaCl solution from a 5M NaCl 2M/5M (.25L) = .1L add 100 mLs of 5M NaCl to 150 mls of water KEY CONCEPTS molecules form when atoms bond to each other chemical bonds are based on electron sharing electron sharing varies from nonpolar covalent bonds, to polar covalent bonds, to ionic bonds of all small molecules, water is the most important for life chemical reactions tend to be spontaneous if they lead to lower potential energy and higher entropy most of the important compounds in organisms contain carbon ACID pH – measure of acidity or basicness log scale – each number represents a power of 10 water is neutral – pH of 7 acidic numbers go down to 0 (10 ) 0 -14 basic numbers go up to 14 (10 ) acid – a substance which releases a proton (positive hydrogen atom) when dissolved in water the extent of dissociation (the amount of protons released compared to the total amount of compound) is a measure of the strength of the acid weak acids & bases act as buffers in biology accept protons and electrons to balance the body’s pH + - HCl dissociates completely in water (very strong) generates free H and Cl an acid is a compound that in an aqueous solution will readily shed a proton a base is a compound that in an aqueous solution will readily accept a proton most living cells have very narrow range of tolerance for pH + every factor of 2 difference in H represents .3 pH to determine the pH of a solution use a pH meter or paper titrate the solution with an indicator dye getting rid of CO 2ecreases acidity in the body – exhaled breath is an acid THE HYDRATION OF CARBON DIOXIDE IN WATER - + CO +2H O 2 H CO 2carb3nic acid) HCO + H (bica3bonate) as carbon dioxide goes into solution, carbonic acid is formed, which partially dissociates, liberating protons & thus causing the solution to become more acidic, lowering the pH NEGATIVE pH [H ] must be greater than 1M indicates a very, very concentrated acid not biologically relevant (battery acid) WEAKACIDS some substances, like acetic acid (vinegar) dissociate poorly in water they release only a small amount of protons serve as good buffers because they only partially dissociate and can reaccept protons weak acids are in equilibrium with their ionized species governed by the Law of MassAction & characterized by an equilibrium constant for any chemical reaction at equilibrium, increasing the amount of any ingredient will drive the reaction in the opposite direction WATER :AVERY WEAKACID + - dissociates from 2 H O2into H O 3 OH not a good buffer, but a good solvent perfect medium for life COMPARATIVE EQUILIBRIUM CONSTANTS water : K eq1.8 * 10 -16 acetic acid : Keq 1.7 * 10 -5 blood pH is between 6.8 to 8.0 slightly basic is optimal to raise pH in blood, add bicarbonate & reduce acidity weak acids have only a modest tendency to shed their protons the corresponding negatively charged anion becomes a willing proton acceptor & is called the conjugate base the properties of a buffer rely on a balance between a weak acid & its conjugate base buffering range : only small pH changes result from addition of base or acid a buffer is a solution of a weak acid & its conjugate base that resists changes in pH in BOTH directions works best in the middle of its range, where the amount of undissociated acid is about equal to the amount of the conjugate base one can soak up excess protons (acid) & the other can soak up excess hydroxide (base) pH control is important, as many enzymes have a narrow range in which they function optimally buffering capability is essential for the well-being of organisms, to protect them from unwelcome changes in pH many compou
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