# PKb of weak base titrated with strong acid

• Chemistry
• i_love_science
In summary, the PKb of a weak base titrated with a strong acid is the negative logarithm of the base dissociation constant of the weak base and is a measure of its strength in a solution. It can be calculated using the Henderson-Hasselbalch equation and gives an indication of how much the weak base will dissociate. The PKb value also affects the equivalence point in a titration and can be used to determine the concentration of the weak base in a solution by using the Henderson-Hasselbalch equation or constructing a titration curve.
i_love_science
Homework Statement
(see below)
Relevant Equations
titration curve
pH + pOH = 14

at halfway point:
pH=pKa
pOH=pKb

What is true about the pK of the analyte?
a) pKa = 9.2
b) pKb = 9.2
c) pKb = 4.8
d) pKa = 11.7

The halfway point is at point 4, at approximately pH=9.2. Therefore, the pOH = pKb = 4.8, and I think the answer is c).
The solution says b) is the correct answer. Could anyone explain why, or whether or not my answer is correct? Thanks.

Solution is wrong.

Not that you are entirely right, c is not the only correct answer.

## 1. What is the definition of PKb?

PKb, or the base dissociation constant, is a measure of the strength of a weak base. It is the negative logarithm of the equilibrium constant for the dissociation of the base into its conjugate acid and hydroxide ions.

## 2. How is PKb related to pKa?

PKb and pKa are inversely related. The lower the PKb value of a base, the stronger it is, and the higher the pKa value of its conjugate acid, the weaker it is. This is because pKa and PKb are both measures of the strength of an acid or base, but in different contexts.

## 3. How do you calculate PKb from experimental data?

To calculate PKb, you need to know the initial concentration of the weak base, the concentration of the strong acid added, and the pH at each point during the titration. From this data, you can plot a titration curve and determine the equivalence point, where the base is completely neutralized. Then, using the Henderson-Hasselbalch equation, you can calculate the PKb value.

## 4. How does temperature affect PKb?

Like most chemical reactions, the dissociation of a weak base is affected by temperature. As temperature increases, the equilibrium constant for the reaction also increases, leading to a decrease in PKb. This means that weak bases become stronger at higher temperatures.

## 5. How does the strength of the weak base affect the PKb value?

The stronger the weak base, the lower its PKb value will be. This is because a stronger base will have a higher concentration of hydroxide ions at equilibrium, making it easier for the base to dissociate and resulting in a lower PKb value.

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