Drill: Determine the pH of 0.25 M HZ. K aHZ = 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 pK a

pK a or pK b pK a = - log K a pK b = - log K b

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

Buffer Problems Calculate the pH of 0.10 M NH 3 in 0.20 M NH 4 NO 3 : K b = 1.8 x 10 -5

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

Buffer Problems Calculate the pH of a solution containing 0.50 M HQ in 0.10 M NaQ: K a = 4.0 x 10 -5

Drill Calculate the pH of a solution containing 0.30 M HZ in 0.10 M NaZ: K a = 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 M HCl

STD Problems Calculate the mass of KHP (MW = ) required to make 1.0 L of M KHP

Henderson- Hasselbach Eq [A - ] [HA] pH = pK a + log

Henderson- Hasselbach Eq [B + ] [B] pOH = pK b + log

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

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

Calculate the HCO 3 - to H 2 CO 3 ratio in blood with pH = 7.40 K a1 for H2CO3 = 4.4 x 10 -7

150 ml of 0.10 M NaOH is added to ml of 0.10 M H 2 CO 3. Calculate all. K a1 for H2CO3 = 4.4 x K a2 for H2CO3 = 4.7 x