Bell Work  NOTE SCHEDULE!  Wed = 8:17 am  Fri = 7:50 am  Due Dates  Acid FRQ & Buffer Sim = TODAY  Lab Notebook = Wed  Buffer FRQ = Fri

Buffers  Weak acid & salt (common ion; conjugate base) HC 2 H 3 O 2 & NaC 2 H 3 O 2  Weak base & salt (common ion; conjugate acid) NH 3 & NH 4 Cl  Resist changes in pH from [H + ] and [OH - ] Based on ratio of buffer components, [HA]/[A - ] or [B]/[BH + ] Salt;CB Weak Acid

Buffer Animation 

Choosing A Good Buffer Equally Protects Against Acids & Bases [HA] = [A - ] [B] = [BH + ] Works in the pH range you wish to maintain Acidic use a weak acid & basic salt buffer Alkaline use a weak base & acidic salt buffer

Choosing A Good Buffer Works in the pH range you wish to maintain….ex: 4.6 weak acid and salt [ ] should match [H + ] = Ka or[OH - ] = Kb [H + ] = = 2.5 x [H + ] = 2.5 x pH = -log [H + ] = 4.6 Ka = 1.8 x pKa = -log Ka= 4.7 acetic acid Small Nasty # Small Nasty # Log It Large Nice # Large Nice #

Choosing A Good Buffer Acidity of soln matches the acidity of the buffer pH = -log [H + ] pKa = - log Ka pH = pKa or pOH = pKb

Henderson – Hasselbalch Equation (H-H) weak acid salt conjugate base ion Ratio of buffer components determines pH change TAKE THE LOG OF THE ENTIER EQUATION -log [ H + ] = -log Ka [HA] [A - ] pH = pKa + log [A - ]/[HA] pOH = pKb + log [BH + ]/[B] Log vs -log Flip Log vs -log Flip

Titration Buffer Zone Half of acid has reacted ½ HA  H + + A - [HA ] acid = [A - ] conjugate Buffer Region [H+] = Ka [HA] [A - ] -log [H + ] = - log Ka pH = pKa and [H+] = Ka

Titration Indicators Choosing an Indicator  Indicator changes color over the equivalence point pH range

Titration Indicators Choosing an Indicator  pKa of indicator is within ± 1 unit of the pH

Hydrolysis Reacting (not dissolving) a salt or salt ion with water  Tool to determine if a salt is acidic of basic  Basic = proton acceptor; creates OH - ions  Acidic = proton donor; creates H + ions  pH water changes based on behavior of the salt  Ka vs Kb

Sample Problem HAH3O+A- I C x x E – 1.66 x x10 -3 Original 10 -2, ions are Can’t ignore Original 10 -2, ions are Can’t ignore

Sample Problem

1.66% = [H + ] x 100 [HC 3 H 5 O 3 ] [H + ] = x 0.50 M = M [H+] = [C 3 H 5 O 3 ] Ka = [0.0083] [0.0083] = 1.4 x [0.50] Only 1.66% Keq ~ Original Only 1.66% Keq ~ Original Account for ions Still Get Same Account for ions Still Get Same

Sample Problem [H + ] = MKa = 1.4 x pH = -log [H + ] = - log (0.0083) pH = 2.08

Sample Problem Weak acid and salt with common ion; Buffer! You have 2 options ICE or HH equation You have 2 options ICE or HH equation Ka = 1.4 x pH = -log (1.4x10 -4 ) log 0.18 =

Sample Problem Strong 100%  H + Strong 100%  H + Only 1.66% Turns into H + Only 1.66% Turns into H + Added Volumes Will Change M Added Volumes Will Change M Ka = 1.4 x 10 -4

Sample Problem Add H+ Will Shift eq Add H+ Will Shift eq Change Insignificant Change Insignificant Ka = 1.4 x 10 -4

Sample Problem Add H+ Will Shift eq Add H+ Will Shift eq Before Adding In HCl After Adding In HCl 1.66% = [C 3 H 5 O 3 - ] x 100 [HC 3 H 5 O 3 ] [C 3 H 5 O 3 - ] = x 0.50 M = M [C 3 H 5 O 3 - ] = M How Does This Illustrate LeChatelier's Principle? How Does This Illustrate LeChatelier's Principle? How Does This Illustrate conjugate pairs Relationship? How Does This Illustrate conjugate pairs Relationship?

Things To Do  Turn In Acid Base FRQ / Buffer Simulation  Lab Report = Due Wed  Buffer FRQ = Due Fri

Homework Lab Report = Due Wed Equilibrium Practice = Due Fri