Drill: A 0.100 M solution of HZ ionizes 20.0 %. Calculate: KaHZ

Review Drill & Discuss Exam (Writing on it) (A Mistake)

Second Semester Syllabus

The SSS is on Poly’s Website

Equilibrium will be a major of the second semester. Review PP-20-22

CHM II HW Review PP-23 Complete the attached assignment & turn it in tomorrow

Buffer Solutions

A solution that resists changes in pH Buffer Solution A solution that resists changes in pH

Made from the combination of a weak acid & its salt Buffer Solution Made from the combination of a weak acid & its salt

Made from the combination of a weak base & its salt Buffer Solution Made from the combination of a weak base & its salt

Buffer Examples Mix acetic acid & sodium acetate Mix ammonia & ammonium chloride

A buffer solution works best when the acid to salt ratio is 1 : 1

A buffer solution works best when the base to salt ratio is 1 : 1

Buffer Solution The buffering capacity of a solution works best when the pH is near the pKa

pKa or pKb pKa = - log Ka pKb = - log Kb

Buffer Equilibria

To solve buffer equilibrium problems, use the same 5 steps

5 Steps of Equilibrium Problems 1) Set up & balance reaction

5 Steps of Equilibrium Problems 2) Assign Equilibrium amounts in terms of x (ICE)

5 Steps of Equilibrium Problems 3) Write the equilibrium expression (K = ?)

5 Steps of Equilibrium Problems 4) Substitute Equilibrium amounts into the K

5 Steps of Equilibrium Problems 5) Solve for x

Calculate the pH of a solution containing Buffer Problems Calculate the pH of a solution containing 0.10 M HAc in 0.10 M NaAc: Ka = 1.8 x 10-5

Calculate the pH of 0.10 M NH3 in Buffer Problems Calculate the pH of 0.10 M NH3 in 0.20 M NH4NO3: Kb = 1.8 x 10-5

Calculate the pH of a solution containing Buffer Problems Calculate the pH of a solution containing 0.10 M HBz in 0.20 M NaBz: Ka = 6.4 x 10-5

Calculate the pH of a solution containing Drill: Calculate the pH of a solution containing 0.30 M HZ in 0.10 M NaZ: Ka = 3.0 x 10-5

Review Drill & Check HW

CHM II HW Review PP-23 Complete the attached assignment & turn it in tomorrow.

Calculate the pH of a solution containing Buffer Problem Calculate the pH of a solution containing 0.50 M R-NH2 in 0.10 M R-NH3I: Kb = 4.0 x 10-5

Derivations from an equilibrium constant

HA H+ + A- [H+][A-] [HA] Ka =

Cross multiply to isolate [H+] HA H+ + A- [H+][A-] [HA] Ka = Cross multiply to isolate [H+]

HA H+ + A- [Ka][HA] [A-] [H+]=

HA H+ + A- [HA] [A-] [H+] = (Ka)

HA H+ + A- [HA] [A-] [H+] = (Ka) Take –log of each side

pH = [HA] [A-] pKa - log

Henderson-Hasselbach Eq pH = pKa + log

Henderson-Hasselbach Eq pOH = pKb+ log

Buffer Problems Calculate the salt to acid ratio to make a buffer solution with pH = 5.0 Ka for HBZ = 2.0 x 10-5

Derivations from an equilibrium constant

HA H+ + A- [H+][A-] [HA] Ka =

[H+][A-] [HA] Ka = Divide both sides by [H+]

You Get the Salt to Acid Ratio Ka [A-] [H+] [HA] = You Get the Salt to Acid Ratio

Drill: Calculate the salt to acid ratio to make a buffer solution with pH = 5.0 Ka for HBZ = 2.0 x 10-5

Review & Collect Drill & HW

CHM II HW Review PPs 23 & 24 Complete the attached assignment & turn it in tomorrow.

Buffer Problems Calculate the salt to base ratio to make a buffer solution with pH = 9.48 Kb for MOH = 2.0 x 10-5

Point at which the # of moles of the two titrants are equal Equivalence Point Point at which the # of moles of the two titrants are equal

Titration Curves

[HA]=[OH-] [HA]=[A-]

Drill: Calculate the pH of a buffer solution containing 0.50 M HX in 0.25 M KX. Ka = 2.5 x 10-5

Test End of next week

Calculate the HCO3- to H2CO3 ratio in blood with pH = 7.40 Ka1 for H2CO3 = 4.4 x 10-7

150 ml of 0. 10 M NaOH is added to 100. 0 ml of 0. 10 M H2CO3 150 ml of 0.10 M NaOH is added to 100.0 ml of 0.10 M H2CO3. Calculate pH. Ka1 for H2CO3 = 4.4 x 10-7 Ka2 for H2CO3 = 4.8 x 10-11