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“A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 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 K a and K b 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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Zn Control of protein shape is due to fraction of sites charged R refers to rest of protein Ionization constants for proteins Phosphoenolate carboxylase, human, cys cysteine

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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 [H 3 O aq +] AND a new vocabulary for comparing the solution acidity from experiment to experiment K a and K b 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 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/baseave [H + ]pHpOH ave [OH - ] baseblood5.01x10 -8 saliva1x10 -7 acidurine2.51x10 -7 cow’s milk 3.54x10 -7 cheese7.94x # is slightly larger than 10 -8, so I know it is 7….. something = x10 -7 You do the rest

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- - cysteine What are the two pK a s? What is the K a of a compound Whose pK a is 3.7?

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“A” students work (without solutions manual) ~ 10 problems/night. Dr. Alanah Fitch Flanner Hall 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 K a s 1.Write down ALL possible reactions involving a proton 2.Excluding water, identify all the proton donors as 1.Strong acid a. Strong electrolyte: HNO 3, HCl, H 2 SO 4 (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 K a; smallest charge density anion c.Calculate how many protons omega gives up (equil) d.Calculate pH e.Use to determine what alpha gets

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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 (H 2 SO 4, HSO 4 - ) 6.Triethylamine 7.NaAcetate 8.Our heme example Calculate the pH of M HCl

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Generalized Strategy involves comparing K a s 1.Write down ALL possible reactions involving a proton 2.Excluding water, identify all the proton donors as 1.Strong acid a.Strong electrolyte: HNO 3, HCl, H 2 SO 4 (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 1.HCl 2.Acetic acid (vinegar) 2.HF 3.B(OH) 3 (Boric acid (eye wash)) 4.Mixture (HF and phenol) 5.Mixture (H 2 SO 4, HSO 4 - ) 6.Triethylamine 7.NaAcetate 8.Our heme example

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1.Write down ALL possible reactions involving a proton 2.Excluding water, identify all the proton donors as 1.Strong acid a. Strong electrolyte: HNO 3, HCl, H 2 SO 4 (None) 2. Weak Acid: 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 HC 2 H 3 O 2. (CH 3 COOH) K a = 1.8x10 -5 Density of 5% acetic acid 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 HC 2 H 3 O 2. (CH 3 COOH) K a = 1.8x10 -5 Density of 5% acetic acid g/mL % by wt. K a = 1.8x10 -5 KnowDon’t Know Need the initial molarity need the final dissociation

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HC 2 H 3 O 2 C 2 H 3 O 2 - H + stoic111 conc. init5% [Init] Change-x+x+x Assume0.8355>>x+x10 -7 << x [Equil] x+x H 2 OOH - H Why complicate this situation by adding in 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 g/mL. Vinegar is acetic acid which has the formula HC 2 H 3 O 2. (CH 3 COOH) K a = 1.8x10 -5

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Check: HAAH + Assume0.8355>>x+x10-7 << 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 g/mL. Vinegar is acetic acid which has the formula HC 2 H 3 O 2. (CH 3 COOH) K a = 1.8x10 -5

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How does % dissociation or ionization vary with concentration? [Acetic Acid]% ionization 1.00M0.42% 0.835M0.46% 0.1M1.3% 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 g/mL. Vinegar is acetic acid which has the formula HC 2 H 3 O 2. (CH 3 COOH) K a = 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 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 (H 2 SO 4, HSO 4 - ) 7.Triethylamine 8.NaAcetate 9.Our heme example

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1.Write down ALL possible reactions involving a proton 2.Excluding water, identify all the proton donors as 1.Strong acid a. Strong electrolyte: HNO 3, HCl, H 2 SO 4 (No Clean Socks) 2. Weak Acid a.Identify strongest acid (omega dog, can not hold protons) b.Has largest K a; smallest charge density anion c.Calculate how many protons omega gives up (equil) Calculate the F- of a solution of 1.00 M HF. K a = 7.2x10 -4 No Strong Acids (SA)

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H 2 OH + OH HF (aq) H + from HF F - stoic.111 Init Change-x +x+x Assum1>>x10 -7 <

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Calculate the pH of a solution of 1.00 M HF. K 1 = 7.2x10 -4 Check assumptions HF (aq) H + from HF F - Init Change-x +x+x Assum1>>x10 -7 <

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Calculate the F- of a solution of 1.00 M HF. K 1 = 7.2x10 -4 HF (aq) H + from HF F - Init Change-x +x+x Assum1>>x10 -7 <

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1.Write down ALL possible reactions involving a proton 2.Identify proton donors 1.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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H 2 OOH - H B(OH) 3 + H 2 O B(OH) H + stoic1n.a.1 1 [Init] Change-x+x +x Assume0.75>>xx <

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B(OH) 3 + H 2 O B(OH) H + [Init] Change-x+x +x Assume0.75>>xx <

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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 (H 2 SO 4, HSO 4 - ) 7.Triethylamine 8.NaAcetate 9.Our heme example

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1.Write down ALL possible reactions involving a proton 2.Excluding water, identify all the proton donors as 1.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 HOC 6 H 5. Calculate the conc. of -OC 6 H 5 at this concentration. NONE

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H 2 OOH - H HF + H 2 O F - + H + stoic1n.a.1 1 [Init] Change-x+x +x Assume1.0>>xx <

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HF + H 2 O F - + H + stoic1n.a.1 1 [Init] Change-x+x +x Assume1.0>>xx <

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HF + H 2 O F - + H + stoic1n.a.1 1 [Init] Change-x+x +x Assume1.0>>xx <

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HF + H 2 O F - + H + stoic1n.a.1 1 [Init] Change-x+x +x Assume1.0>>xx <

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C 6 H 5 OH+ H 2 O C 6 H 5 O - + H + stoic1n.a.1 1 [Init] x10 -2 Change-x+x +x Assume1.0>>xx x<<2.7x10 -2 Equil1.0x 2.7x10 -2 Calculate the pH of a solution that contains 1.0 M HF and 1.0 M HOC 6 H 5. Calculate the conc. of -OC 6 H 5 at this concentration.

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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 (H 2 SO 4, HSO 4 - ) 7.Triethylamine 8.NaAcetate 9.Our heme example

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1.Write down ALL possible reactions involving a proton 2.Excluding water, identify all the proton donors as 1.Strong acid a.Strong electrolyte: HNO 3, HCl, H 2 SO 4 (No Clean Socks) b. Give all strong acid protons to water or alpha dog Example: calculate the pH of M sulfuric acid

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Example: calculate the pH of M sulfuric acid; K a2 = 1.2x10 -2 Pure WaterH 2 OOH - H Control/complete H 2 SO 4 HSO 4 - H + stoic.111 [init] complete stoic.HSO 4 - H + SO [Init] Change-x +x+x Assume?0.0010>x >x +x [Equil] x NO!

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Example: calculate the pH of M sulfuric acid; K a2 = 1.2x10 -2 stoic.HSO 4 - H + SO [Init] Change-x +x+x Assume?0.001>x 0.001>x+x [Equil]0.001-x xx Here is our first example in which we can not make assumptions

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[SO 4 2- ]=x -Solution gives a neg Number which is not allowed [H + ]= pH=-log( )=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 M HNO 2 using the iterative method (K a =6.0x10 -4 ) Pure WaterH 2 OOH - H HNO 2 NO 2 H + stoic.111 [Init] Change-x+x+x Assume0.100>>xxx>>10 -7 [Equil]0.100xx Calc 17.7x10 -3 New Equil x10 -3 x’’ x’’ Calc x10 -3 New New Equil x10 -3 x’’’x’’’ Calc x

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Converging, plausible answer for iterative method: M HNO 2, K a =6.0x10 -4

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

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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 (H 2 SO 4, HSO 4 - ) 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, K b = 4.0x10 -4 Calc. the [OH], [H], and pH of 0.20 M solns of triethylamine, K b = 4.0x10 -4 H 2 OH + OH BH 2 OBH + OH- stoic1111 [Init] Change-x+x+x Assum0.20>>xx10 -7 < x Equil0.20xx 1 2

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Calc. the [OH], [H], and pH of 0.20 M solns of triethylamine, K b = 4.0x10 -4 H 2 OH + OH BH 2 OBH + OH- stoic1111 [Init] Change-x+x+x Assum0.20>>xx10 -7 < x Equil0.20xx 1 2 Rounds to Rounds to 0.20

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

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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 (H 2 SO 4, HSO 4 - ) 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? K a = 1.8x10 -5 Write all reactions involving protons, hydroxides Determine who is omega and will donate Hmm, a slight problem – we don’t know K b

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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? K a = 1.8x10 -5

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H 2 OH + OH CH 3 COO - + H 2 O = CH 3 COOH + OH - stoich111 [Init] Change-x+x x Sum0.1-x0+x x Assumex >>10 -7 [Equil]0.1xx 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? K a = 1.8x10 -5

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CH 3 COO - + H 2 O = CH 3 COOH + OH - stoich111 [Init] Change-x+x x Sum0.1-x0+x x Assumex >>10 -7 [Equil]0.1xx 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? K a = 1.8x10 -5 yes No

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CH 3 COO - + H 2 O = CH 3 COOH + OH - stoich111 [Init] Change-x+x x Sum0.1-x0+x x Assumex >>10 -7 [Equil]0.1xx Equil new0.1-xxx 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? K a = 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 Office Hours Th&F 2-3:30 pm Biological Chemistry Module #17B: Acid Base Ionization Computations

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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 (H 2 SO 4, HSO 4 - ) 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 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 Cl 2 given that at 35 o C the equilibrium constant, K c, is 1.6x10 -5 mol/L? Red herrings: Clues? 35 o C 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! K c is Example 2 EXAMPLE 3: K c = 0.36M Example 4: K p is 1x Module 17A

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We want to know when assumptions are valid. HA (aq) H + from HA A - InitHA INIT Change-x +x+x EquilHA INIT -x xx %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=KA= x x Error too large Error OK Never make assumption Safe to make assumptioniffy

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Small K ~ <10 -6 Rule of Thumb Sort of small

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K= %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 Office Hours Th&F 2-3:30 pm Module #17B: Acid Base Ionization Computations

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ExamplesKInit Conc.x>10 -7 ? HSO x yes Triethylamine4x yes HF7.2x yes Acetic Acid1.8x yes Acetate5.55x no Boric Acid5.8x

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