What is pKb?
pKb is the criterion used to estimate the alkalinity of the molecule. It is used to measure basic strength. The lesser the pKb is, the more potent the base will be. It is equivalent to the negative logarithm of base dissociation constant, Kb.
pKb = – log Kb
What is Kb?
Kb or base dissociation constant is the criterion used to estimate a base’s strength. It tells us about how much a base dissociates in an aqueous solution. Kb is used in distinguishing a strong base from a weak base. More the value of Kb more would be its dissociation.
Table of Content
- Understanding Kb and pKb in detail
- pKb to Kb
- pKb value of few bases
- Frequently Asked Questions – FAQs
Understanding Kb and pKb in detail
pKb is the criterion used to estimate the alkalinity of the molecule. It is used to measure basic strength. The lesser the pKb is, the more potent the base will be. It is equivalent to the negative logarithm of base dissociation constant, Kb.
pKb = – log Kb
- The larger the value of pKb weaker would be the base.
In contrast, Kb or base dissociation constant is the criterion used to estimate a base’s strength. It tells us about how much a base dissociates in an aqueous solution. Kb is used in distinguishing a strong base from a weak base. More the value of Kb more would be its dissociation.
Consider dissociation of base BOH:
BOH ⥦ B+ + OH–
For the above reaction, the base dissociation constant Kb would be,
Whereas
pKb = – log Kb
Here, quantities in the square brackets are the equilibrium concentration.
A strong base will dissociate into its constituent ions quickly. Thus, we can say that a strong base has a larger Kb. If the concentration of B+ and OH– is more, the Kb value would increase.
pKb to Kb
We can convert pKb to Kb as
pKb = – logKb
– pKb = log Kb
e – (pKb) = Kb
Kb = e-(pKb).
The dissociation constant of a strong base is as high as 102, while a weak base has as low as 10-10, which is quite challenging to remember. So to ease that, pKb came into existence.
We know that
pKb = -log Kb.
Putting the base dissociation constant value in the equation, we get -2 pKb for a strong base and 10 pKb for a weak base.
pKb value of few bases
| S. No. | Name of the Base | pKb value |
|---|---|---|
| 1 | Lithium Hydroxide | -0.36 |
| 2 | Potassium Hydroxide | 0.5 |
| 3 | Sodium Hydroxide | 0.2 |
| 4 | Ammonia | 4.76 |
Frequently Asked Questions on pKb to Kb
What is pKb?
pKb is the criterion used to estimate the alkalinity of the molecule. It is used to measure basic strength. The lesser the pKb is, the more potent the base will be. It is equivalent to the negative logarithm of base dissociation constant, Kb.
pKb = – log Kb
What is Kb?
Kb or base dissociation constant is the criterion used to estimate a base’s strength. It tells us about how much a base dissociates in an aqueous solution. Kb is used in distinguishing a strong base from a weak base. More the value of Kb more would be its dissociation.
How will you convert pKb to Kb?
We can convert pKb to Kb as,
pKb = – logKb
– pKb = log Kb
e – (pKb) = Kb
Kb = e-(pKb).
What is the chemical importance of pKb?
The dissociation constant of a strong base is as high as 102, while a weak base has as low as 10-10, which is quite challenging to remember. So to ease that, pKb came into existence.
We know that
pKb = -log Kb.
Putting the base dissociation constant value in the equation, we get -2 pKb for a strong base and 10 pKb for a weak base, which is easy to remember.
Are Kb and pKb related?
Yes, Kb and pKb are related.
pKb = – log Kb
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