1.) If a STRONG ACID is added to a buffer system… Review: 1.) If a STRONG ACID is added to a buffer system… H3O+ + HCO3 -  H2O + H2CO3 The strong acid reacts with the conjugate base of the buffer solution 2.) If a STRONG BASE is added… OH- + H2CO3  H2O + HCO3- The strong base reacts with the weak acid of the buffer solution

Finding the pH of a buffer solution: What is the pH of a 1.00 Liter acetic acid / sodium acetate buffer with [CH3CO2H] = 0.70 M and [CH3CO2-] = 0.60 M? (CH3CO2H, Ka=1.8x10-5) What buffering reaction would take place if sodium hydroxide were added to this buffer? How many moles of NaOH could be added before the buffer stopped working?

Objectives: 1. Describe how to produce a buffer solution with certain pH

Preparing a Buffer Solution: 1. Buffers are prepared by combing an acid solution with a salt containing the conjugate base ie. Mix hydrofluoric acid, HF, solution with sodium fluoride, NaF You must also be sure to use a salt that is actually soluble in water! (alkali metals are the safest bet)

Preparing a Buffer Solution: 1. Buffers are prepared by combing an acid solution with a salt containing the conjugate base 2. pH is controlled primarily by the pKa of the acid being used.

Preparing a Buffer Solution: 1. Buffers are prepared by combing an acid solution with a salt containing the conjugate base 2. pH is controlled primarily by the pKa of the acid used. 3. pH is “fine tuned” by the ratio of acid : base

Preparing a Buffer Solution: Which of the following acid-base pairs would be a suitable choice for the creation of a buffer solution with a pH of 4.3? In what ratio should they be? HSO4- SO42- Ka=1.2x10-2 pKa=1.92 HC2H3O2 C2H3O21- Ka=1.8x10-5 pKa=4.75 HCO3- CO32- Ka=4.8x10-11 pKa=10.32

Buffer Creation: Available chemicals: Unlimited 6 M stock solutions of acetic acid Unlimited amounts of sodium acetate solid salt Unlimited deionized water Describe steps on how to produce 100 mL of a buffer with assigned pH. Be specific about how much 6 M acid solution to dilute and what mass of salt to add. This should be types/written and turned in at the end of the period.

Acids and Bases