Drill: Determine the pH of 0.25 M HZ.KaHZ = 2.5 x 10-7

Buffer Solutions

Buffer Solution

•A solution that resists changes in

pH

Buffer Solution•Made from the combination of a weak acid & 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

Buffer Solution•A buffer solution

works best when the acid to salt ratio is

1 : 1

Buffer Solution•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 Problems•Calculate the pH of a solution containing 0.10

M HAc in 0.10 M NaAc: Ka = 1.8 x 10-5

Buffer Problems•Calculate the pH of 0.10 M NH3 in 0.20

M NH4NO3:

•Kb = 1.8 x 10-5

Buffer ProblemsCalculate the pH of a

solution containing

0.10 M HBz in 0.20 M NaBz: Ka = 6.4 x 10-5

Buffer ProblemsCalculate the pH of a

solution containing

0.50 M HQ in 0.10 M NaQ: Ka = 4.0 x 10-5

DrillCalculate the pH of a

solution containing

0.30 M HZ in 0.10 M NaZ: Ka = 3.0 x 10-5

Lab Requirements• To make accurate

measurements, we must have solutions with accurately measured concentrations

Standard Solution•A solution with known concentration

•2.004 M HCl

STD ProblemsCalculate the mass of KHP (MW = 204.23)

required to make 1.0 L of 0.100 M KHP

Henderson-Hasselbach Eq

[A-]

[HA]pH = pKa + log

Henderson-Hasselbach Eq

[B+]

[B]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

Buffer ProblemsCalculate the salt to base

ratio to make a buffer solution with pH = 9.48

• Kb for MOH = 2.0 x 10-5

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. Calculate all.

• Ka1 for H2CO3 = 4.4 x 10-7

• Ka2 for H2CO3 = 4.7 x 10-11