H2O F H OH OH bonds are polar and can dissociate heterolytically Bond breaking in which the bonding electron pair is split unevenly between the products Products are a proton ti and a hydroxide 10h 01 1 Dissociation of water is a rapid reversible process Most water molecules remain un ionized thus pure water has very low electrical conductivity The equilibrium is strongly to the left 110W Kea H Hydronium ion gives up a proton Hyo I1 11 1107 yy H Proton hop H 1 11110 H V Go H 1 H H 0 1 1 The extent of dissociation depends on the temperature 21 1 0 1 130 A 81k OH a protons do not exist freely in solution They are immediately hydrated to form hydronium 10ns 1 130 1 keg can be determined experimentally it is 1 8 10 1 1 at 25 C Keg HHj 1 1 0 can be determined from water density 1 1555 5119 A hydronium ion is a water molecule with a proton associated with one of the nonbonding electron pairs tonic product Of water Kw keg 1 10 1 1 1 OH 7 1 1 0 M2 In pure water H 01 1 10 74 2 Hydronium ions are solvated by nearby water molecules The covalent and hydrogen bonds are interchangeable allows for an extremely fast mobility of protons in water 111A proton hopping pH log H Kw H OH 1 1 10 11 12 log H log 01 5 14 PH POH 4 pH and POH must always add up 1014 In neutral and pH can be negative 1 1 1 614 pH Scale OH JCM Poti 0 IN HCl 2 Lemon Juice 4 acidic 5 Red wine Beer Black coffee I h Gastric Juice g a 9lY Cola vinegar gg Milk Human blood tears seawater egg white 9 Increasingly solution of baking 7 N 7dral Household ammonia Household bleach Saliva 11 IMNAOH 13 14 H M 10 l 1 10 ii 10 3 4 10 5 10 6 10 10 105 10 10 3 10 10 14 pH 0 1 a 3 5 6 8 a 10 I 12 13 14 Strong Acids THEE iM EE E E cid 15482 E E E THE P TREE THAT Hydrochloric Acid Nitric Hydrolodlc Acid Perohloric Acid Chloric Acid Dissociate completely into their 10ns in water yielding one or more proteins per molecule 14 10 10 13 ion 10 11 10 10 4 8 10 14 13 n It 10 9 8 Weak Acids 7 10 7 io oc MN TFcqM qTFF IF E E E E ii 10 4 10 3 10 2 Phosphoric Methanol C Sulfurous Acid Acid Acid s 3 4 2 MMF 9M E T E cid 15482 E Hydrofluoric Acid Do Not Dissociate completely into their 10ns In water yielding one or more proteins per molecule Most organic acids are weak adds significant in biological functions 10 10011 1 0 Weak Electrolyte Dissociation Hzc 1 120 ea Hzc 0 1 130 Acetic Acid Weak electrolytes dissociate only partially in water Ka H CH COO c 4 10 74 Extent of dissociation is determined by the acid dissociation constant ka Hzc 41 F Hzc H ka O 0 0 OH A 0 1 B 0 1 can calculate pH if Kats known A M Ka l 4 10 2 1 74 10 G 1 74 10 B Ka L 4 l M 1 74 10 b 11 0 001310 pH 2 883 11 0 00132 pH 2 880 PKa Measures Acidity pka 1091ha CHGC CH3C pka 4 6 N Hj t NH I CHI 0 pKa 2 34 Hzcoz HCO H pka 3 7 NHI cid 15482 1111 13 1 1 pka 9 25 HCO 3 F CO 11 1 pKa 10 2 cid 15482 pKa 9 60 Hypo Hzpo 4 1 1 1 pKa 2 14 HZPO 4 HPO PKa 6 86 HPO cid 15482 PO H mospnonca io EFTTF 59 oo mFE EI cid 15482 oE Trlprotlc Acids 2 3 4 5 6 7 8 9 10 11 12 13 Monoprotlc acids Acetic acids 11149 1 74 10 514 Ammonium ton ka 5 62 10 1 1 Dlprotlc acids carbonic Acids ka 1 70 10 m Bicarbonate ka 6 31 10 M Glycine Carboxyl ka 4 57 10 3114 Glycine amino Ika 2 51 10 1 1 ka 7 25 10 314 I Dihydrogen phosphate ka 1 38 10 7M Monohydrogen Phosphate Ka 3 98 10 13M Buffers Mixtures of Weak Acids and Their Conjugate Base At pH pka there is a 50 50 mixture f d and f MP Buffering capacity of acid Anton system IS greatest at pH pKa guy mg aapa y wn p g from pKa by more than I PH UNIT Henderson Hasselbatch Equation HA 1 i A ka H P 6 7 j Buffering q cid 15482 5 G 4 a 2 oH com g 3 re pH 3 76 0 10 2 0 30 4 0 50 6 0 70 8 0 9 1 0 OH added equivalents 5 0 O 100 Percent titrated H ka 10g H tog ka 109 H fg pH pKa 110g HA Biological Buffer Systems Maintenance Of Intracellular pH is vital to all cells Enzyme catalyzed reactions have optimal pH solubility of polar molecules depends on H bond donors and acceptors Equilibrium between CO2 gas and dissolved Hcoj depends on pH Buffer systems in vivo are mainly based on phosphate concentration in mini molar range bicarbonate important for blood plasma histidine efficient buffer at neutral pH Buffer Systems in vitro are often based on sulfonic acids of cyclic amines HEPES PIPES HO CHES N N SO Na