Transcript Slide 1
“A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 [email protected] Office Hours Th&F 2-3:30 pm Module #17B: Acid Base Ionization Computations To determine if our protein unfolds or not is it sufficient to know the Ka and Kb Values of the functional groups? 2 1 3D structure of ALAD directs Reactants into proper orientation 3D structure controlled by proper hydrogen and ionic bonds, pH dependent!!!!!!! http://www.jenner.ac.uk/PPD/ http://www.biology.arizona.edu/biochemistry/problem_sets/aa/aa.htm Ionization constants for proteins O C S- S- Zn2+ - O H S RCOOHaq H2 O RCOO H O aq 3 aq RSHaq H2 O RS H O aq 3 aq R refers to rest of protein cysteine Ka ,COOH 10 . x10 2 Ka,SH 6.3x10 9 Phosphoenolate carboxylase, human, cys Ka 7.94 x10 9 Control of protein shape is due to fraction of sites charged Protein folding due to FRACTION of sites charged Ka,Val , NH3 2.5x1010 Ka ,Val ,COOH 501 . x10 3 Ka,tyr ,ROH 10 . x1010 Hemeglobin % Ionized (dissociated) HAaq H O 3 aq , from HA Aaq amount dissociated ( M ) %dissociation 100 initial concentration ( M ) Aaq % dissociation 100 HA aq ,initial This seems pretty straight forward Calculating [A-] This will require knowing [H3Oaq+] aq HA Ka aq , from HA H3 O Aaq ,eq H 3 Oaq ,eq HA eq ,aq aq A AND a new vocabulary for comparing the solution acidity from experiment to experiment Ka and Kb tell us about the possibility Of donating protons, not what the solution Acidity is Define another comparison number: pH “A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 [email protected] Office Hours Th&F 2-3:30 pm Module #17B: Acid Base Ionization Computations pH, pOH, pKa LAZY Chemists are _____ To shorten calculations use log log ab log a logb a log log a log b p x log x b x log a x log a 1 x log x loga x log a a K OH H O eq 3 eq H O 2 2 Assumption that 55.5 molar is relative unchanged K H2 O 2 H O OH eq H 3 O eq 2 K 5555 . OH eq 3 eq K5555 . KW 1014 2 KW 10 14 OHeq H3Oeq KW 10 14 OHaq H3 Oaq log KW log10 14 log OH 14 aq logOH aq log H O 14 log OH 3 aq logH O 3 aq aq log H O 3 aq p x log x 14 pOH pH pH scale runs from 0 to 14 Which is more Acidic? acid/base ave [H+] base blood 5.01x10-8 saliva 1x10-7 acid urine 2.51x10-7 cow’s milk 3.54x10-7 cheese 7.94x10-6 pH pOH ave [OH-] 7.3 6.7 7 You do the rest pH log501 . x108 7.3 # is slightly larger than 10-8, so I know it is 7….. something 14-7.3=6.7 1.99x10-7 [OH ] 10 6.7 1995 . x10 7 p x log x 14 pH pOH x 10 pX What are the two pKas? px 1log x O C pKa 1 log6.3x10 9 S- - O H pKa 1 8.2 8.2 RCOOHaq H2 O RCOO H O aq 3 a cysteine What is the Ka of a compound Whose pKa is 3.7? x 10 px 3.7 4 Ka 10 199 . x10 Ka ,COOH 10 . x10 2 Ka,SH 6.3x10 9 “A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 [email protected] Office Hours Th&F 2-3:30 pm Module #17B: Acid Base Ionization Computations Calculating [A-] This will require an equilibrium calculation aq HA Ka aq , from HA H3 O Aaq ,eq H 3 Oaq ,eq HA eq ,aq aq A Generalized Strategy involves comparing Kas 1. Write down ALL possible reactions involving a proton 2. Excluding water, identify all the proton donors as 1. Strong acid a. Strong electrolyte: HNO3, HCl, H2SO4 (No Clean Socks) b. Give all strong acid protons to water or alpha dog c. Calculate hydronium conc. d. Calculate pH 2. Weak Acid a. Identify strongest acid (omega dog, can not hold protons) b. Has largest Ka; smallest charge density anion c. Calculate how many protons omega gives up (equil) d. Calculate pH e. Use to determine what alpha gets Example Calculations 1.HCl 2.Acetic acid (vinegar) 2.HF 3.B(OH)3 (Boric acid (eye wash)) 4.Mixture (HF and phenol) 5.Mixture (H2SO4, HSO4-) 6.Triethylamine 7.NaAcetate 8.Our heme example Calculate the pH of 0.004 M HCl Generalized Strategy involves comparing Kas 1. Write down ALL possible reactions involving a proton HClaq H Cl aq aq H2 O H OH aq aq Kw 10 14 2. Excluding water, identify all the proton donors as 1. Strong acid a. Strong electrolyte: HNO3, HCl, H2SO4 (No Clean Socks) Cl low ch arg e density Omega dog aq b. Give all strong acid protons to water or alpha present H2 O HClaq give all bone to water complete reaction H3Oaq Claq c. Calculate hydronium conc. d. Calculate pH H3Oaq 0.004 M H3Oaq 0.004 M Scientific notation allows you to quickly check if Your answer is in the right “ballpark” pH log4x10 3 3 pH log 4 log10 pH log 4 3 pH 0.602 3 pH 2.39 pH has to be slightly less Than 3 Example Calculations 1.HCl 2.Acetic acid (vinegar) 2.HF 3.B(OH)3 (Boric acid (eye wash)) 4.Mixture (HF and phenol) 5.Mixture (H2SO4, HSO4-) 6.Triethylamine 7.NaAcetate 8.Our heme example Example: What is the % ionization of commercial vinegar? The label reads 5% acidity (by weight). Vinegar is acetic acid which has the formula HC2H3O2. (CH3COOH) Ka = 1.8x10-5 Density of 5% acetic acid 1.0023 g/mL 1. Write down ALL possible reactions involving a proton CH3COOHaq H2 O H O CH COO 3 aq , 3 aq H2 O H OH aq aq Ka 18 . x10 5 Kw 10 14 2. Excluding water, identify all the proton donors as 1. Strong acid a. Strong electrolyte: HNO3, HCl, H2SO4 (None) 2. Weak Acid: CH3COOHaq H2 O H3 Oaq , CH3 COOaq Ka 18 . x10 5 a. Calculate how many protons omega gives up (equil) Example: What is the % ionization of commercial vinegar? The label reads 5% acidity (by weight). Vinegar is acetic acid which has the formula HC2H3O2. (CH3COOH) Ka = 1.8x10-5 Density of 5% acetic acid 1.0023g/mL Don’t Know Know Need the initial molarity need the final dissociation % by wt. Ka = 1.8x10-5 5g acetic acid 100 g solution 5g acetic acid 100 g solution 1moleacetic acid 5gacetic acid 5g acetic acid 60 g acetic acid 0.083mole 0.835 M 0.0997 L 0.0997 L 1mLsolution 1L 100g solution 10023 . g solution 10 3 mL 1moleacetic acid 212 41 216 . M HC H O 08355 2 3 2 Why complicate this situation by adding in 10-7 When we get rid off it with an assumption? Because it creates a habit necessary of multiple rx H2O OH55.5 10-7 HC2H3O2 C2H3O2stoic 1 1 conc. init 5% 0 [Init] 0.8355 0 Change -x +x Assume 0.8355>>x +x [Equil] 0.8355 +x What is the % ionization of commercial vinegar? The label reads 5% acidity (by weight). Density of 5% acetic acid is 1.0023 g/mL. Vinegar is acetic acid which has the formula HC2H3O2. (CH3COOH) Ka = 1.8x10-5 Ka x x 10 7 H+ 10-7 H+ 1 10-7 10-7 +x 10-7 << x +x x2 HA x HA init init 18 . x10 5 x2 0.8355 HA 0.8355>>x Assume 08355 . Ka x A +x 2 0.8355 Ka x x 18. x105 0.8355 0.003878 7 10 0.003878 Check: 0.0038780 + 0.0000001 0.0039779 Sig figs H+ 10-7 << x 08355 . 0003878 . ? 0.835500 0.003878 0.831622 Original sig figs were = 0.83 So if we round to 2 sig fig, have Same answer pH =-log(0.003878)= 2.41 A aq ,eq % dissociation 100 HA aq ,initial 0.003878 100 0.46% 0.835 What is the % ionization of commercial vinegar? The label reads 5% acidity (by weight). Density of 5% acetic acid is 1.0023 g/mL. Vinegar is acetic acid which has the formula HC2H3O2. (CH3COOH) Ka = 1.8x10-5 How does % dissociation or ionization vary with concentration? [Acetic Acid] 1.00 M 0.835M 0.1 M % ionization 0.42% 0.46% 1.3% Observations? % ionization increases with the lower molarity. Why should this be so? What is the % ionization of commercial vinegar? The label reads 5% acidity (by weight). Density of 5% acetic acid is 1.0023 g/mL. Vinegar is acetic acid which has the formula HC2H3O2. (CH3COOH) Ka = 1.8x10-5 H A Ka HA Dilute by 10 (make less concentrated): H A 10 10 H A Q , , K ? HA HA10 10 What does this tell us, if anything? We have too many reactants, need to shift to the right, or dissociate some more. general rule of thumb: dilution gives more dissociation. Example Calculations 1.HCl 2.Acetic acid (vinegar) 3.HF 4.B(OH)3 (Boric acid (eye wash)) (students Do this one yourself) 5.Mixture (HF and phenol) 6.Mixture (H2SO4, HSO4-) 7.Triethylamine 8.NaAcetate 9.Our heme example Calculate the F- of a solution of 1.00 M HF. Ka= 7.2x10-4 1. Write down ALL possible reactions involving a proton HFaq H F aq , F aq H2 O H OH aq aq Ka 7.2 x10 4 Kw 10 14 2. Excluding water, identify all the proton donors as 1. Strong acid a. Strong electrolyte: HNO3, HCl, H2SO4 (No Clean Socks) No Strong Acids (SA) 2. Weak Acid a. Identify strongest acid (omega dog, can not hold protons) b. Has largest Ka; smallest charge density anion HFaq H F aq , F aq Ka 7.2 x10 4 c. Calculate how many protons omega gives up (equil) stoic. Init Change Assum Equil H 2O 55.5 HF(aq) 1 1.0 -x 1>>x 1 H+ 10-7 H+from HF 1 10-7 +x 10-7 <<x x OH10-7 F1 0 +x x Init Change Assum Equil x x Ka HA 1 K x init 2 a x 2.7 x10 H+from HF F10-7 0 +x +x 10-7 <<x x x HF(aq) 1.0 -x 1>>x 1 Check assumptions 1 2.7 x10 2 1 10 7 2.7 x10 2 0.027 0.027 0.0000001 0.983 0.0270001 2 Calculate the pH of a solution of 1.00 M HF. K1 = 7.2x10-4 Sig fig is here 0983 . 1 00270001 . 0027 . Init Change Assum Equil HF(aq) 1.0 -x 1>>x 1 x 2.7 x10 2 x F 2.7x10 2 pH log2.7x10 2 1568 . 16 . Calculate the F- of a solution of 1.00 M HF. K1 = 7.2x10-4 H+from HF F10-7 0 +x +x 10-7 <<x x x Example: Boric acid is commonly used in eyewash solutions to neutralize bases splashed in the eye. It acts as a monoprotic acid, but the dissociation reaction looks different. Calculate the pH of a 0.75 M solution of boric acid, and the concentration of B(OH)4-. B OH 3,aq H2 O B OH H O 4 ,aq 3 aq Ka 58 . x10 10 1. Write down ALL possible reactions involving a proton B OH 3,aq H2 O B OH 4 ,aq H3Oaq H2 O H OH aq aq Ka 58 . x10 10 Kw 10 14 2. Identify proton donors 1. strong acids: No Clean Socks? 2. Weak acids: No SA Students do B(OH)3 This on your own Set up ICAE chart stoic [Init] Change Assume Equil Ka x2 HA Students do This on your own OHH+ 10-7 10-7 B(OH)4- + H+ 1 1 0 10-7 +x +x x 10-7<<x x x H 2O 55.5 B(OH)3 + H2O 1 n.a. 0.75 -x 0.75>>x 0.75 58. x1010 0.75 x 2.1x10 5 init 2 x 58 . xcheck?? 10 10 two assumptions. B(OH) + H O B(OH) + H K = 5.8x10 Calculate the pH of a 0.75 M solution of boric acid. 0.75 3 2 4 - + a -10 B(OH)4- + H+ 0 10-7 +x +x x 10-7<<x x x B(OH)3 + H2O 0.75 -x 0.75>>x 0.75 [Init] Change Assume Equil 58. x1010 0.75 075 . x ? yes x 10 7 ? 0.000021 x 2.1x10 5 5 x B OH 4 2.1x10 x H 21 . x105 pH log21 . x105 4.68 4.7 0.0000001 0.0000211two assumptions. check?? B(OH) Sig fig Students do This on your own + H2O B(OH)4- + H+ Ka = 5.8x10-10 Calculate the pH of a 0.75 M solution of boric acid. 3 Example Calculations 1.HCl 2.Acetic acid (vinegar) 3.HF 4.B(OH)3 (Boric acid (eye wash)) (students Do this one yourself) 5.Mixture (HF and phenol) 6.Mixture (H2SO4, HSO4-) 7.Triethylamine 8.NaAcetate 9.Our heme example Mixtures of Acids Calculate the pH of a solution that contains 1.0 M HF and 1.0 M HOC6 H5. Calculate the conc. of -OC6 H5 at this concentration. 1. Write down ALL possible reactions involving a proton HFaq H F aq , F aq C6 H5OH H C H O aq 6 5 aq H2 O H OH aq aq Ka 7.2 x10 4 Ka 18 . x10 5 Kw 10 14 2. Excluding water, identify all the proton donors as 1. Strong acid NONE 2. Weak Acid Identify strongest acid (omega dog, can not hold protons) Has largest Ka; smallest charge density anion Calculate how many protons omega gives up (equil) Calculate pH (Use to determine what alpha gets) HF will control the proton concentration, but Should include all possible sources to remind ourselves. stoic [Init] Change Assume Equil Ka OH10-7 F- + 1 0 +x x x H 2O 55.5 HF + H2O 1 n.a. 1.0 -x 1.0>>x 1.0 x2 x2 1 7.2 x10 4 HA init 7.2 x10 4 check?? H two assumptions. +F K = 7.2x10 HF HOC6 H5 + - H+ + -OC6 H5 a -4 Ka = 1.8x10-5 H+ 10-7 H+ 1 10-7 +x 10-7<<x x x 2.7 x10 2 Calculate the pH of a solution that contains 1.0 M HF and 1.0 M HOC6 H5. Calculate the conc. of -OC6 H5 at this concentration. stoic [Init] Change Assume Equil HF + H2O 1 n.a. 1.0 -x 1.0>>x 1.0 7.2 x10 4 x 2.7 x10 2 Check assumptions: 2.7 x10 2 1 10 . 0.027 F- + 1 0 +x x x H+ 1 10-7 +x 10-7<<x x 2.7 x10 2 107 0.027 0.0000001 0.0270001 0.983 Sig fig = 1.0 Sig fig = 0.027 F- + H+ 1 1 0 10-7 +x +x x 10-7<<x x x 2.7 x10 C H O HF + H2O 1 n.a. 1.0 -x 1.0>>x 1.0 stoic [Init] Change Assume Equil 7.2 x10 4 x 2.7 x10 H x 2.7x10 2 2 2 Ka 18 . x10 5 C H O pH 157 . 6 5 aq C6 H5 OH H2 O H O C H O 3 aq 6 5 aq Ka 18 . x10 5 H O C H O 3 aq 6 5 C H OH 6 5 aq 6 5 aq 1 18 . x105 4 6 . 66 x 10 2.7 x10 2 Ka 18 . x10 5 Calculate the pH of a solution that contains 1.0 M HF and 1.0 M HOC6 H5. Calculate the conc. of -OC6 H5 at this concentration. Example Calculations 1.HCl 2.Acetic acid (vinegar) 3.HF 4.B(OH)3 (Boric acid (eye wash)) (students Do this one yourself) 5.Mixture (HF and phenol) 6.Mixture (H2SO4, HSO4-) 7.Triethylamine 8.NaAcetate 9.Our heme example Example: calculate the pH of 0.0010 M sulfuric acid 1. Write down ALL possible reactions involving a proton H2 SO4 ,aq H2 O HSO H O 4 aq , F 3 aq 2 HSO4 ,aq H2 O H O SO 3 aq 4.aq H2 O H OH aq aq Ka l arg e Ka 12 . x10 2 Kw 10 14 2. Excluding water, identify all the proton donors as 1. Strong acid a. Strong electrolyte: HNO3, HCl, H2SO4 (No Clean Socks) H2 SO4 ,aq H2 O HSO H O 4 aq , F 3 aq Ka l arg e b. Give all strong acid protons to water or alpha dog 1 2 3 Pure Water Control/complete stoic. [init] complete stoic. H2O 55.5 H2SO4 1 .001 0 [Init] Change Assume? [Equil] Ka 2 12 . x10 2 H O SO 3 aq 2 4.aq HSO4,aq OH10-7 HSO41 0 0.001 HSO41 0.0010 -x 0.001>x 0.001 H+ 10-7 H+ 1 10-7 0.001+10-7 H+ SO421 1 0. 0010 0 +x +x 0.001>x +x 0.001 x 0.001 x Ka2 12 . x10 0.001 2 Ka 2 12 . x10 2 x SO42,aq Example: calculate the pH of 0.0010 M sulfuric acid; Ka2 = 1.2x10-2 Ka2 12 . x10 2 x 10 . x10 3 NO! HSO41 0.0010 -x 0.001>x 0.001-x stoic. [Init] Change Assume? [Equil] H+ 1 0. 0010 +x 0.001>x 0.001+x SO421 0 +x +x x Here is our first example in which we can not Make assumptions Ka 2 12 . x10 2 H O SO 3 aq 2 4.aq HSO4,aq 0.001 x x Ka2 12 . x10 0.001 x 2 . x10 2 0.001 x 0.001 x x 12 12 . x10 5 12 . x10 2 x 0.001x x 2 x 2 0.001x 12 . x10 2 x 12 . x10 5 0 Example: calculate the pH of 0.0010 M sulfuric acid; Ka2 = 1.2x10-2 x 2 0.013x 12 . x10 5 0 x 2 0.013x 12 . x10 5 0 2 0.013 0.013 41 0.000012 x 21 x 0.013 2.17 x10 2 4 0.013 0.0147 x 2 x 8.65x10 [SO42-]=x 4 ax 2 bx c 0 x b b 2 4ac 2a -Solution gives a neg Number which is not allowed [H+]=0.001 +0.000865 0.001865 pH=-log(0.001865)=2.73 Successive Approximations (iterations) Alternative Strategy to going to “exact equil. Expression” ITERATIVE SOLUTIONS Why? – because the real body or real world Is much too complex to always be able to Find an exact equilibrium expression Calculate proton concentration of 0.100 M HNO2 using the iterative method (Ka=6.0x10-4) Pure Water H2O OHH+ 1 55.5 10-7 10-7 HNO2 NO2 H+ stoic. 1 1 1 0.1 0 10-7 2 [Init] Change -x +x +x Assum 0.1>>x x x>>10-7 [Equil] 0.1 x x Calc 7.7x10-3 New Equil 0.1-7.7x10-3 x’’ x’’ 3 New calc 7.44x10-3 -3 x’’’ New New Equil 0.1-7.44x10 x’’’ 4 New new Calc 7.45x10-3 Ka 6.0 x10 x 4 x2 01 . . 7.7 x10 3 6.0x10 4 01 x' ' x'' . 7.7 x10 3 7.7 x10 3 6.0x10 4 01 5538 . x105 7.44 x10 3 Converging, plausible answer for iterative method: 0.100 M HNO2, Ka=6.0x10-4 Can Skip This for BLB “A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 [email protected] Office Hours Th&F 2-3:30 pm Module #17B: Acid Base Ionization Computations Weak Bases Example Calculations 1.HCl 2.Acetic acid (vinegar) 3.HF 4.B(OH)3 (Boric acid (eye wash)) (students Do this one yourself) 5.Mixture (HF and phenol) 6.Mixture (H2SO4, HSO4-) 7.Triethylamine 8.NaAcetate 9.Our heme example Calculation with Weak Base Calc. the [OH], [H], and pH of 0.20 M solns of triethylamine, Kb = 4.0x10-4 1 stoic 2 [Init] Change Assum Equil B 1 0.20 -x 0.20>>x 0.20 H 2O 55.5 H 2O 1 Calc. the [OH], [H], and pH of 0.20 M solns of triethylamine, Kb = 4.0x10-4 H+ 10-7 BH+ 1 0 +x x x OH10-7 OH1 10-7 +x 10-7 < x x 1 stoic 2 [Init] Change Assum Equil B 1 0.20 -x 0.20>>x 0.20 7 x 10 x x 2 4 Kb 4.0x10 0.20 x 0.2 4.0x10 4 0.2 x 8.94 x10 3 8.94 x10 3 10 7 ? H+ 10-7 BH+ 1 0 +x x x H2O 55.5 H2O 1 0.00894 OH10-7 OH1 10-7 +x 10-7 < x x 0.2 0.00000001 0.00894 0.00895001 019106 . Rounds to 0.2 Rounds to 0.0089 8.94 x10 3 0.2 ? Calc. the [OH], [H], and pH of 0.20 M solns of triethylamine, Kb = 4.0x10-4 x OH 8.94x10 3 pOH 2.048 pH 14 2.048 1195 . “A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 [email protected] Office Hours Th&F 2-3:30 pm Module #17B: Acid Base Ionization Computations Salts Example Calculations 1.HCl 2.Acetic acid (vinegar) 3.HF 4.B(OH)3 (Boric acid (eye wash)) (students Do this one yourself) 5.Mixture (HF and phenol) 6.Mixture (H2SO4, HSO4-) 7.Triethylamine 8.NaAcetate 9.Our heme example Write all reactions involving protons, hydroxides NaCH3COO H2 O Na CH COO aq 3 aq CH3COOaq H2 O OH aq CH3 COOHaq aq H2 O Na no reaction H2 O H OH aq aq Kw 10 14 Determine who is omega and will donate CH3COOaq H2 O OH aq CH3 COOHaq Hmm, a slight problem – we don’t know Kb If we place Na acetate in solution (to make a 0.1 M solution) what are the main species present? What will be the pH of the solution? Ka = 1.8x10-5 CH3COOHaq H2 O CH COO H O 3 aq 3 aq aq aq CH3COO H3O + 1 Ka CH3COOHaq H2 O H2 O H OH aq aq aq Ka 18 . x10 5 CH3COO H2 O Kw 10 14 CH3COOHaq OH aq 1 Kw Ka Kw Ka Kb 10 14 10 K 555 . x 10 b 18 . x10 5 If we place Na acetate in solution (to make a 0.1 M solution) what are the main species present? What will be the pH of the solution? Ka = 1.8x10-5 14 pKa pKb Kb 555 . x1010 1 2 stoich [Init] Change Sum Assume [Equil] H2O H+ OH55.5 10-7 10-7 CH3COO- + H2O = CH3COOH + OH1 1 1 0.1 0 10-7 -x +x 10-7 +x 0.1-x 0+x 10-7 +x x<<<0.1 x>>>10-7 0.1 x x If we place Na acetate in solution (to make a 0.1 M solution) what are the main species present? What will be the pH of the solution? Ka = 1.8x10-5 CH3COO- + H2O = CH3COOH + OH1 1 1 0.1 0 10-7 -x +x 10-7 +x 0.1-x 0+x 10-7 +x x<<<0.1 x>>>10-7 0.1 x x stoich [Init] Change Sum Assume [Equil] Kb 555 . x10 555 . x10 10 OH aq CH 3 COOH aq CH COO 3 555 . x10 10 x 7.45x10 6 10 aq x10 7 x x 2 01 . x 01 . . x10 10 01 . 555 x 7.45x10 6 01 . ? 7.45x10 6 10 7 ?? yes X100 rule No If we place Na acetate in solution (to make a 0.1 M solution) what are the main species present? What will be the pH of the solution? Ka = 1.8x10-5 CH3COO- + H2O = CH3COOH + OHstoich 1 1 1 [Init] 0.1 0 10-7 Change -x +x 10-7 +x Sum 0.1-x 0+x 10-7 +x Assume x<<<0.1 x>>>10-7 [Equil] 0.1 x x Equil new 0.1-x x x+10-7 7 x 10 x 10 Kb 555 . x10 01 . x . x1010 01 . x x107 x 107 x x 2 555 If we place Na acetate in solution (to make a 0.1 M solution) what are the main species present? What will be the pH of the solution? Ka = 1.8x10-5 555 . x1011 555 . x1010 x 10 7 x x 2 x 2 107 x 555 . x1010 x 555 . x1011 0 x 2 100555 . x107 x 555 . x1011 0 ax 2 bx c 0 x 100555 . x10 7 2 . x10 7 41555 . x10 11 100555 21 100555 . x10 7 101103 . x10 14 2.22 x10 10 x 2 100555 . x10 7 149 . x10 5 x 7.399 x10 6 2 Before we got 7.45x10-6 b b 2 4ac x 2a “A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 [email protected] Office Hours Th&F 2-3:30 pm Module #17B: Acid Base Ionization Computations Biological Chemistry Example Calculations 1.HCl 2.Acetic acid (vinegar) 3.HF 4.B(OH)3 (Boric acid (eye wash)) (students Do this one yourself) 5.Mixture (HF and phenol) 6.Mixture (H2SO4, HSO4-) 7.Triethylamine 8.NaAcetate 9.Our heme example Protein folding due to FRACTION of sites charged Ka,Val , NH3 2.5x1010 Ka ,Val ,COOH 501 . x10 3 Ka,tyr ,ROH 10 . x1010 Hemeglobin EXAMPLE Which pH (2, 7, 11) is most favorable for the formation of a hydrogen bond between Val and tyr in hemoglobin It would be useful to be able to predict fraction ionized at all pH values Without knowing the concentration of the protein acid sites. Skill would be useful in other equilibrium Calculations. Need to arrange equations to get Rid of equilibrium concentrations HAaq H2 O H O 3 aq , from HA HA H H init init x init A init 0 x H HA A H HA A H HA A H Aeq Ka init init init eq init init eq init A HA init init x A A A A A A A init eq Hinit A HA Aaq eq eq eq eq eq eq eq f ionized x HA init Ka H A HA A init f ionized init Aeq HA init K A H A H A K A A H K Ka HAinit A Hinit A K HA K HA Ka HAinit a init a init init a init init A a Ka a Ka A H K HA init a init H K HA init a init An alternative method To this equation is on next Slide (can be skipped) Here is an alternative way to get the equation HAaq H2 O f dissociated aq , from HA H3 O A HA f dissociated 3 eq ,aq f dissociated A H O A K aq ,eq A aq ,eq 3 aq ,eq aq ,eq a f dissociated 1 H O 1 3 A HA A aq ,eq eq aq ,eq aq ,eq a Mass balance 3 eq ,aq aq ,eq init A aq ,eq A H O HA K aq ,eq HAinit HAeq ,aq Aaq ,eq Ka aq A HO HA aq ,eq Ka aq ,eq f dissociated Ka H O K 3 aq ,eq a 1 0.9 f ionized ,val RCOO aq ,val RCOOH f ionized ,tyr init 0.8 RO aq ,tyr RCOH Fraction Ionized init 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 2 4 6 8 10 12 14 pH Which pH will allow best H-bonding? 16 “A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 [email protected] Office Hours Th&F 2-3:30 pm Module #17B: Acid Base Ionization Computations When should we Be making assumptions? Example on Using Simplifications Module 17A If 1.0 mol NOCl is placed in a 2.0 L flask what are the equilibrium concentrations of NO and Cl2 given that at 35 oC the equilibrium constant, Kc, is 1.6x10-5 mol/L? Red herrings: 35 oC is a red herring Clues? K is “small” compared to others (<<< 1) we have worked with !!!!! Example 2 EXAMPLE 3: Example 4: CO2 , g H2 , g COg H2 Og N 2 O4 2 NO2 ( g ) H2 , g I 2 , g 2 HI ( g ) Kc is 0.64. Kc = 0.36M Kp is 1x10-2. We will define Small in the Next chapter! The issue is small Ka with respect To the initial concentration!! Considering a simple system HAeq A H eq eq The issue is small Ka with respect To the initial concentration!! Considering a simple system HAeq A H eq eq A HA K Mass balance aq ,eq HA HA A init aq ,eq eq ,aq A aq ,eq % dissociated HA A eq aq ,eq Ka A HO HA aq ,eq 3 aq ,eq aq ,eq 3 aq ,eq eq ,aq aq ,eq 100 eq ,aq a HA K eq ,aq a Ka HAeq %dissociated HAeq Ka HAeq 100 OK this is not a nice equation Do you need to know it? eq ,aq A H O HA K A 2 a “A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 [email protected] Office Hours Th&F 2-3:30 pm Module #17B: Acid Base Ionization Computations What you need To know 1.pH, pOH, pKa, pKb 2.Fraction Ionized 3.ICE charts for equilibrium calculation 4.Recognize a fraction ionized chart and interpret it 5.Recognize when you can make “assumptions” “A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 [email protected] Office Hours Th&F 2-3:30 pm Module #17B: Acid Base Ionization Computations END Which pH (2, 7, 11) is most favorable for the formation of a hydrogen bond between Val and tyr in hemoglobin Ka ,Val ,COOH 501 . x10 3 % dissociated aq ,eq 100 A Ka,tyr ,ROH 10 . x1010 A H O A K aq ,eq aq ,eq 3 aq ,eq a % dissociated 100 H O 1 3 aq ,eq Ka pH 2 7 11 [H+] 1.00E-02 1.00E-07 1.00E-11 pH2 10 2 100 100 % dissociatedCOOH 33.33 % dissociatedCOOH 10 2 2 10 3 1 5.01x10 3 1 5.01x10 KaCOOH Ka ROH 5.00E-03 1.00E-10 %diss %diss 33.33333 1E-06 99.998 0.0999 100 90.90909 Repeat procedure With tyrosine Ka ,Val ,COOH 501 . x10 3 Ka,tyr ,ROH 10 . x1010 Which pH is best? pH 2 7 11 [H+] 1.00E-02 1.00E-07 1.00E-11 KaCOOH Ka ROH 5.00E-03 1.00E-10 %diss %diss 33.33333 1E-06 99.998 0.0999 100 90.90909