Podcast
Questions and Answers
What can you say about Kb tables?
What can you say about Kb tables?
- They are equal to Ka
- You can't find Kb from Ka
- They usually don't exist (correct)
- They usually exist
How do you find Kb from Ka?
How do you find Kb from Ka?
Kb = (10^-14)/Ka
What is the relationship between pKa and pKb?
What is the relationship between pKa and pKb?
pKa + pKb = 14
If pKa = 10, what is the pKb of sodium phenoxide?
If pKa = 10, what is the pKb of sodium phenoxide?
How do you calculate the concentration of pyridine needed to produce a solution with a pH of 8?
How do you calculate the concentration of pyridine needed to produce a solution with a pH of 8?
What does a 0.25M weak base solution with a pH of 9.25 indicate regarding its Kb?
What does a 0.25M weak base solution with a pH of 9.25 indicate regarding its Kb?
Which of the following indicates the strongest conjugate base?
Which of the following indicates the strongest conjugate base?
What can be said about the conjugate bases of strong acids?
What can be said about the conjugate bases of strong acids?
What can be said about the conjugate bases of weak acids?
What can be said about the conjugate bases of weak acids?
Where can you find the diagrams of the strength of acid-base pairs?
Where can you find the diagrams of the strength of acid-base pairs?
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Study Notes
Kb and Its Characteristics
- Kb tables are not commonly available despite every acid having a conjugate base, implying a relationship between Ka and Kb.
- Kb can be derived from Ka using the formula: Kb = (10^-14) / Ka.
Relationship Between pKa and pKb
- The relationship is defined by the equation: pKa + pKb = 14.
Example Calculations
- For sodium phenoxide with a pKa of 10:
- pKb is calculated as 14 - 10 = 4.
- Thus, Kb = 10^-4.
Concentration Calculations
-
To find the concentration of pyridine needed for a pH of 8:
- Convert pH to [OH-]eq.
- Use the Kb reaction and known values to calculate Kb.
-
A 0.25 M weak base with a pH of 9.25:
- Determine [OH-]eq from pH.
- Use the ICE table approach to calculate Kb.
Identifying Conjugate Bases
- The strongest conjugate base is found from the weakest acid:
- E (pKa = 10) has the highest pKa and lowest Ka, indicating it has the strongest conjugate base.
Conjugate Bases of Acids
- The conjugate bases of strong acids are very weak bases and generally incapable of acting as bases. This is due to their complete dissociation in solution.
- The conjugate bases of weak acids are categorized as weak bases.
Visual Aids
- Consult notes for diagrams illustrating the strength of acid-base pairs to enhance understanding.
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