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

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# Drill: Determine the pH of 0.25 M HZ. K aHZ = 2.5 x 10 -7 - PowerPoint PPT Presentation

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 &amp; its salt. Buffer Solution. Made from the combination of a weak base &amp; its salt. Buffer Examples.

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Presentation Transcript
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 Problems

Calculate the pH of a solution containing

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

Buffer Problems

Calculate the pH of a solution containing

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

Drill

Calculate 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 Problems

Calculate 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 Problems

Calculate the salt to base ratio to make a buffer solution with pH = 9.48

• Kb for MOH = 2.0 x 10-5
• Ka1 for H2CO3 = 4.4 x 10-7
• Ka1 for H2CO3 = 4.4 x 10-7
• Ka2 for H2CO3 = 4.7 x 10-11