17B Acid Base Equilibria final version

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“A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours Th&F 2-3:30 pm Module #17B: Acid Base Ionization Computations

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To determine if our protein unfolds or not is it sufficient to know the Ka and Kb Values of the functional groups?

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3D structure of ALAD directs Reactants into proper orientation 2 1 3D structure controlled by proper hydrogen and ionic bonds, pH dependent!!!!!!!

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Zn2+ Control of protein shape is due to fraction of sites charged R refers to rest of protein Phosphoenolate carboxylase, human, cys cysteine http://www.biology.arizona.edu/biochemistry/problem_sets/aa/aa.html

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Protein folding due to FRACTION of sites charged Hemeglobin

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% Ionized (dissociated) This seems pretty straight forward

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Calculating [A-] This will require knowing [H3Oaq+] 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

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“A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours Th&F 2-3:30 pm pH, pOH, pKa Module #17B: Acid Base Ionization Computations

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Chemists are _____ To shorten calculations use log LAZY

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Assumption that 55.5 molar is relative unchanged

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pH scale runs from 0 to 14 Which is more Acidic?

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acid/base ave [H+] pH pOH ave [OH-] base blood 5.01x10-8 saliva 1x10-7 acid urine 2.51x10-7 cow’s milk 3.54x10-7 cheese 7.94x10-6 7.3 7 # is slightly larger than 10-8, so I know it is 7….. something 14-7.3=6.7 6.7 1.99x10-7 You do the rest

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cysteine What are the two pKas? What is the Ka of a compound Whose pKa is 3.7?

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“A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours Th&F 2-3:30 pm Module #17B: Acid Base Ionization Computations

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Calculating [A-] This will require an equilibrium calculation

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Generalized Strategy involves comparing Kas Write down ALL possible reactions involving a proton Excluding water, identify all the proton donors as 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 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

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Example Calculations HCl Acetic acid (vinegar) HF B(OH)3 (Boric acid (eye wash)) Mixture (HF and phenol) Mixture (H2SO4, HSO4-) Triethylamine NaAcetate Our heme example Calculate the pH of 0.004 M HCl

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Generalized Strategy involves comparing Kas Write down ALL possible reactions involving a proton Excluding water, identify all the proton donors as Strong acid Strong electrolyte: HNO3, HCl, H2SO4 (No Clean Socks) b. Give all strong acid protons to water or alpha present c. Calculate hydronium conc. d. Calculate pH Omega dog

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Scientific notation allows you to quickly check if Your answer is in the right “ballpark” pH has to be slightly less Than 3

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Example Calculations HCl Acetic acid (vinegar) HF B(OH)3 (Boric acid (eye wash)) Mixture (HF and phenol) Mixture (H2SO4, HSO4-) Triethylamine NaAcetate Our heme example

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Write down ALL possible reactions involving a proton Excluding water, identify all the proton donors as Strong acid a. Strong electrolyte: HNO3, HCl, H2SO4 (None) 2. Weak Acid: 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 1.0023 g/mL

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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 % by wt. Ka = 1.8x10-5 Know Don’t Know Need the initial molarity need the final dissociation

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HC2H3O2 C2H3O2- H+ stoic 1 1 1 conc. init 5% 0 10-7 [Init] 0.8355 0 10-7 Change -x +x +x Assume 0.8355>>x +x 10-7 << x [Equil] 0.8355 +x +x H2O OH- H+ 55.5 10-7 10-7 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 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

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Check: HA A H+ Assume 0.8355>>x +x 10-7 << x Sig figs + - Original sig figs were = 0.83 So if we round to 2 sig fig, have Same answer

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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

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How does % dissociation or ionization vary with concentration? [Acetic Acid] % ionization 1.00 M 0.42% 0.835M 0.46% 0.1 M 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

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Dilute by 10 (make less concentrated): 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.

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Example Calculations HCl 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

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Write down ALL possible reactions involving a proton Excluding water, identify all the proton donors as Strong acid a. Strong electrolyte: HNO3, HCl, H2SO4 (No Clean Socks) 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 the F- of a solution of 1.00 M HF. Ka= 7.2x10-4 No Strong Acids (SA)

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H2O H+ OH- 55.5 10-7 10-7 HF(aq) H+from HF F- stoic. 1 1 1 Init 1.0 10-7 0 Change -x +x +x Assum 1>>x 10-7 <<x Equil 1 x x

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Calculate the pH of a solution of 1.00 M HF. K1 = 7.2x10-4 Check assumptions HF(aq) H+from HF F- Init 1.0 10-7 0 Change -x +x +x Assum 1>>x 10-7 <<x Equil 1 x x Sig fig is here

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Calculate the F- of a solution of 1.00 M HF. K1 = 7.2x10-4 HF(aq) H+from HF F- Init 1.0 10-7 0 Change -x +x +x Assum 1>>x 10-7 <<x Equil 1 x x

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Write down ALL possible reactions involving a proton Identify proton donors strong acids: No Clean Socks? 2. Weak acids: 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-. No SA B(OH)3 Students do This on your own

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H2O OH- H+ 55.5 10-7 10-7 B(OH)3 + H2O B(OH)4- + H+ stoic 1 n.a. 1 1 [Init] 0.75 0 10-7 Change -x +x +x Assume 0.75>>x x 10-7<<x Equil 0.75 x x check?? two assumptions. Set up ICAE chart B(OH)3 + H2O B(OH)4- + H+ Ka = 5.8x10-10 Calculate the pH of a 0.75 M solution of boric acid. Students do This on your own

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B(OH)3 + H2O B(OH)4- + H+ [Init] 0.75 0 10-7 Change -x +x +x Assume 0.75>>x x 10-7<<x Equil 0.75 x x check?? two assumptions. B(OH)3 + H2O B(OH)4- + H+ Ka = 5.8x10-10 Calculate the pH of a 0.75 M solution of boric acid. yes Sig fig Students do This on your own

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Example Calculations HCl 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

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Write down ALL possible reactions involving a proton Excluding water, identify all the proton donors as Strong acid 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) 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. NONE

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H2O OH- H+ 55.5 10-7 10-7 HF + H2O F- + H+ stoic 1 n.a. 1 1 [Init] 1.0 0 10-7 Change -x +x +x Assume 1.0>>x x 10-7<<x Equil 1.0 x x check?? two assumptions. HF will control the proton concentration, but Should include all possible sources to remind ourselves. 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. HF H+ + F- Ka = 7.2x10-4 HOC6 H5 H+ + -OC6 H5 Ka = 1.8x10-5

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HF + H2O F- + H+ stoic 1 n.a. 1 1 [Init] 1.0 0 10-7 Change -x +x +x Assume 1.0>>x x 10-7<<x Equil 1.0 x x Sig fig = 1.0 Check assumptions: Sig fig = 0.027

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HF + H2O F- + H+ stoic 1 n.a. 1 1 [Init] 1.0 0 10-7 Change -x +x +x Assume 1.0>>x x 10-7<<x Equil 1.0 x x 1.0 2.7x10-2 2.7x10-2 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.

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HF + H2O F- + H+ stoic 1 n.a. 1 1 [Init] 1.0 0 10-7 Change -x +x +x Assume 1.0>>x x 10-7<<x Equil 1.0 2.7x10-2 2.7x10-2 C6H5OH+ H2O C6H5O- + H+ stoic 1 n.a. 1 1 [Init] 1.0 0 2.7x10-2 Change -x +x +x Assume 1.0>>x x x<<2.7x10-2 Equil 1.0 x 2.7x10-2

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C6H5OH+ H2O C6H5O- + H+ stoic 1 n.a. 1 1 [Init] 1.0 0 2.7x10-2 Change -x +x +x Assume 1.0>>x x x<<2.7x10-2 Equil 1.0 x 2.7x10-2 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.

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Example Calculations HCl 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

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Write down ALL possible reactions involving a proton Excluding water, identify all the proton donors as Strong acid Strong electrolyte: HNO3, HCl, H2SO4 (No Clean Socks) b. Give all strong acid protons to water or alpha dog Example: calculate the pH of 0.0010 M sulfuric acid

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Example: calculate the pH of 0.0010 M sulfuric acid; Ka2 = 1.2x10-2 Pure Water H2O OH- H+ 55.5 10-7 10-7 Control/complete H2SO4 HSO4- H+ stoic. 1 1 1 [init] .0010 0 10-7 complete 0 0.0010 0.0010+10-7 0 0.0010 0.0010 stoic. HSO4- H+ SO42- 1 1 1 [Init] 0.0010 0. 0010 0 Change -x +x +x Assume? 0.0010>x 0.0010>x +x [Equil] 0.0010 0.0010 x 1 2 3 NO!

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Example: calculate the pH of 0.0010 M sulfuric acid; Ka2 = 1.2x10-2 stoic. HSO4- H+ SO42- 1 1 1 [Init] 0.0010 0. 0010 0 Change -x +x +x Assume? 0.001>x 0.001>x +x [Equil] 0.001-x 0.001+x x Here is our first example in which we can not make assumptions

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[SO42-]=x Solution gives a neg Number which is not allowed [H+]=0.001 +0.000865 0.001865 pH=-log(0.001865)=2.73

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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 Successive Approximations (iterations)

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Calculate proton concentration of 0.100 M HNO2 using the iterative method (Ka=6.0x10-4) Pure Water H2O OH- H+ 55.5 10-7 10-7 HNO2 NO2 H+ stoic. 1 1 1 [Init] 0.100 0 10-7 Change -x +x +x Assume 0.100>>x x x>>10-7 [Equil] 0.100 x x Calc 1 7.7x10-3 New Equil 0.100-7.7x10-3 x’’ x’’ Calc 2 7.44x10-3 New New Equil 0.100-7.44x10-3 x’’’ x’’’ Calc 3 7.45x10-3 1 2 3 4

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Converging, plausible answer for iterative method: 0.100 M HNO2, Ka=6.0x10-4

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“A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours Th&F 2-3:30 pm Weak Bases Module #17B: Acid Base Ionization Computations

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Example Calculations HCl 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

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Calculation with Weak Base Calc. the [OH], [H], and pH of 0.20 M solns of triethylamine, Kb = 4.0x10-4 Calc. the [OH], [H], and pH of 0.20 M solns of triethylamine, Kb = 4.0x10-4 H2O H+ OH- 55.5 10-7 10-7 B H2O BH+ OH- stoic 1 1 1 1 [Init] 0.20 0 10-7 Change -x +x +x Assum 0.20>>x x 10-7 < x Equil 0.20 x x 1 2

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Calc. the [OH], [H], and pH of 0.20 M solns of triethylamine, Kb = 4.0x10-4 H2O H+ OH- 55.5 10-7 10-7 B H2O BH+ OH- stoic 1 1 1 1 [Init] 0.20 0 10-7 Change -x +x +x Assum 0.20>>x x 10-7 < x Equil 0.20 x x 1 2 Rounds to 0.0089 Rounds to 0.20

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“A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours Th&F 2-3:30 pm Salts Module #17B: Acid Base Ionization Computations

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Example Calculations HCl 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

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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 Write all reactions involving protons, hydroxides Determine who is omega and will donate Hmm, a slight problem – we don’t know Kb

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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

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H2O H+ OH- 55.5 10-7 10-7 CH3COO- + H2O = CH3COOH + OH- stoich 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 1 2 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

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CH3COO- + H2O = CH3COOH + OH- stoich 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 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 yes No

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CH3COO- + H2O = CH3COOH + OH- stoich 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 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

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Before we got 7.45x10-6

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“A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours Th&F 2-3:30 pm Biological Chemistry Module #17B: Acid Base Ionization Computations

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Example Calculations HCl 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

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Hemeglobin

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Which pH (2, 7, 11) is most favorable for the formation of a hydrogen bond between Val and tyr in hemoglobin assuming that we define favorable as having the most possible H bonds. Mass balance

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Which pH (2, 4.7, 7, 11) is most favorable for the formation of a hydrogen bond between Val and tyr in hemoglobin assuming that we define favorable has having the most possible H bonds Repeat procedure With tyrosine

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Which pH is best? Hint: Want Val ionized Tyr not ionized

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“A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours Th&F 2-3:30 pm Module #17B: Acid Base Ionization Computations When should we Be making assumptions?

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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: Clues? 35 oC is a red herring K is “small” compared to others (<<< 1) we have worked with !!!!! Example on Using Simplifications We will define Small in the Next chapter! Kc is 0.64. Example 2 EXAMPLE 3: Kc = 0.36M Example 4: Kp is 1x10-2. Module 17A

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We want to know when assumptions are valid. HA(aq) H+from HA A- Init HAINIT 10-7 0 Change -x +x +x Equil HAINIT-x 10-7 +x x %ionized Consider a generic Weak Acid

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The issue is small Ka with respect To the initial concentration!! Mass balance Considering a simple system Do you need to know it? OK this is not a nice equation Hint: no red box

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KA= 10-1 10-2 10-3 10-4 5x10-5 5x10-6 10-7 Error too large Error OK Never make assumption Safe to make assumption iffy

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Small K ~ <10-6 Rule of Thumb Sort of small 10-6<K<10-4 Large K ~>10-3

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K=10-11 10-10 10-9 10-8 10-7 5%error What about the other assumption? contribution of OH- or H+ – x>>10-7

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Rule of thumb Must worry about proton contribution

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“A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 402 508-3119 afitch@luc.edu Office Hours Th&F 2-3:30 pm Module #17B: Acid Base Ionization Computations

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Examples K Init Conc. x>10-7? HSO4- 1.2x10-2 0.001 yes Triethylamine 4x10-4 0.2 yes HF 7.2x10-4 1.0 yes Acetic Acid 1.8x10-5 0.8355 yes Acetate 5.55x10-10 0.1 no Boric Acid 5.8x10-10 0.75