Review- Acid/Base theory

Br¯nsted-Lowry Acid- Substance that increases [H⁺]

Br¯nsted-Lowry Base- Substance that decreases [H⁺]

ÝÝÝÝÝÝÝÝÝ pH = -log[H⁺] ;ÝÝÝÝÝ higher [H⁺] = lower pH

Equilibrium ConstantÝÝÝÝÝÝ K_eq =Ý [products]

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ [reactants]

ÝÝÝÝÝÝÝÝÝ for self-ionization of waterÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ H₂O Ý DÝÝ H⁺ÝÝÝ +ÝÝÝ OH^-

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ K_eqÝÝÝÝ =ÝÝÝ [ H⁺ ] [OH^-]ÝÝÝÝÝÝÝÝÝÝÝÝÝ for [H₂O] =Ý 1000g/LÝÝ =Ý 55.5 M

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ ÝÝÝÝÝÝÝÝÝÝ [H₂O]ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ 18 g/mol

ÝÝÝÝÝÝÝÝÝ given that [ H⁺ ]Ý = [OH^-]Ý =Ý 1.0 x 10^-7 M

ÝÝÝÝÝÝÝÝÝ then ÝÝÝÝÝÝÝÝÝÝÝ K_eq = (1.0 x 10^-7)( 1.0 x 10^-7)ÝÝÝÝ =ÝÝÝ 1.8 x 10^-16

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ 55.5

thereforeÝÝÝÝÝ [ H⁺ ] [OH^-] =(K_eq )(55.5) = (1.8 x 10^-16)(55.5)Ý = 1.0 x 10^-14Ý = K_w

K_w ý Ion Product of water.Ý This describes that the concentration of hydrogen ions

and hydroxide ion are inversely proportional.

Ý

Can we calculate pH whenÝ [ H⁺ ]Ý = [OH^-]Ý

ÝÝÝÝÝÝÝÝÝ pH =Ý - log [ H⁺ ]ÝÝ =ÝÝ - log (1.0 x 10^-7)ÝÝÝ =ÝÝ 7

So, whenÝ [ H⁺ ]Ý = [OH^-] , the solution is neutral.

Ionization Constant (K_a)- describes the ability of an acid to form ions in solution.

ÝÝÝÝÝÝÝÝÝ For strong electrolytes: ( like strong acids)

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ HClÝÝÝ +ÝÝ H₂0ÝÝ ý H₃O⁺Ý ÝÝ +ÝÝÝ Cl^-

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ So K_eq ÝÝÝÝÝÝÝ =Ý [ H₃O⁺ ] [Cl^- ] Ý >> 1 (much larger than one)

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ ÝÝÝÝ [ HCl ][ H₂0 ]ÝÝÝÝÝÝÝ

ÝÝÝÝÝÝÝÝÝ SoÖ this says that in solution, the prevalent forms areÝ H₃O⁺Ý and Cl^-

ÝÝÝÝÝÝÝÝÝ Weak Electrolytes.Ý Do they strongly dissociate?

ÝÝÝÝÝÝÝÝÝ Acetic AcidÝ (CH₃COOH)

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ CH₃COOHÝ +Ý H₂OÝÝ ý CH₃COO^-ÝÝÝ +Ý H₃O⁺

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ ÝK_eq = ÝÝÝ Ý[CH₃COO^- ][H₃O⁺] ÝÝÝÝ, but with weak electrolytes, [H₂O] remains

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ ÝÝÝÝÝ [CH₃COOH][H₂O]ÝÝÝÝÝÝ very large and almost unchanged. IGNORE IT.

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ ÝÝÝÝÝÝÝÝÝ Ý K_aÝ =ÝÝÝÝ Ý[CH₃COO^- ][H₃O⁺] ÝÝÝÝ=ÝÝÝ 1.74 x 10^-5

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ ÝÝÝÝÝÝÝÝÝÝÝÝÝ ÝÝÝÝÝÝÝ[CH₃COOH]

ÝÝÝÝÝÝÝÝÝ So what does this mean?

Strength of Acids/Bases with conjugates.

Relating pH and K_a values. The Henderson-Hasselbalch Equation

ÝÝÝÝÝÝÝÝÝ K_a describes the equilibrium concentrations of the ionic forms and acid forms.

ÝÝÝÝÝÝÝÝÝ What does pH depend on?

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ

ÝÝÝÝÝÝÝÝÝ The amount of H⁺ in solution is dependent upon the amount of acid that has been

dissociated.

In other words [H⁺] = [A^-], given the equation:Ý HAÝ +Ý H₂O ý H₃O^+Ý +Ý A^-

Deriving Henderson-Hasselbalch,

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ K_aÝ =ÝÝÝÝ Ý[A^- ][H₃O⁺] ÝÝÝÝÝ

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ [HA]

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ [H₃O⁺]ÝÝ =ÝÝ K_aÝ [HA]

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ Ý [A^- ]ÝÝÝÝÝÝÝÝÝ

ÝÝÝÝÝÝÝÝÝ Take (-log) of both sidesÝÝÝÝÝÝÝÝÝÝ pHÝ =Ý pKaÝ - log [HA]

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ ÝÝÝÝÝÝÝÝ [A^-]

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ pH = pKaÝ +Ý log [A^-]

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ ÝÝÝÝÝÝ [HA]

ÝÝÝÝÝÝÝÝÝ

ÝÝÝÝÝÝÝÝÝ Can we find the pH when a weak acid is ‡ dissociated if we know the K_a ?

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ pHÝ = -log K_aÝÝ when [A^-]= [HA],ÝÝÝÝÝÝÝÝÝÝÝ because if [A^-] = [HA], then log 1 = 0

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ

pH of HAc (@ [Ac^-] = [HAc])Ý = - log (1.74 x 10^-5)Ý = 4.76

ÝÝÝÝÝÝÝÝÝ Does the initial concentration of HCl affect the pH?

ÝÝÝÝÝÝÝÝÝ Does the initial concentration of HAc affect the pH?

Changes in pH as a function in changes in [A^-] or [HA]

What happens if the pH of an amino acid solution is decreased? Increased?

Example.Ý If the pH is 2 units below the pK_a

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ pH =Ý pK_a + log [A^-]ÝÝ ýÝ pH =Ý pK_a +(-2)

ÝÝÝÝ [HA]

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ therefore:ÝÝÝÝ log [A^-]ÝÝÝÝÝ =ÝÝ -2

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ ÝÝÝÝÝ [HA]

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ (take 10^ of both sides)ÝÝÝÝÝÝÝÝÝÝÝÝ [A^-]ÝÝ = 0.01

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ ÝÝÝÝ ÝÝÝÝÝÝÝÝÝÝÝÝÝ ÝÝÝÝÝÝÝÝÝÝ[HA]

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ What does this mean?

ÝÝÝÝÝÝÝÝÝ The pK_a of Formic Acid is 3.75.Ý Calculate using the Henderson-Hasselbalch equation the pH of a solution containing 200 mL of 0.1 M Formic acid and 150 mL of 0.1 NaOH with enough water bring the entire solution volume to 1 L.

Titrations of Amino Acids

ÝÝÝÝÝÝÝÝÝ

ÝÝÝÝÝÝÝÝÝ ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ Ý

ÝÝÝÝÝÝÝÝÝÝÝÝ

What doÝ pK_a1 Ý& pK_a2 mean?

ÝÝÝÝÝÝÝÝÝ Where does the Isoelectric point exist?Ý What does it mean?

Solving for Isoelectric point

pIÝ =Ý pK_a1 Ý+Ý pK_a2ÝÝÝ

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ 2

ÝÝÝÝÝÝÝÝÝ For alanine, the pI equals

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ pI =Ý 2.3 + 9.7Ý = 6

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ ÝÝ 2

ÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝÝ

ÝÝÝÝÝÝÝÝÝ So, what does this mean?

ÝÝÝÝ

ÝÝÝÝÝÝÝÝÝ

ÝÝÝÝÝÝÝÝÝ Calculate the pI for Glutamic Acid.