pKa meaning

[almaortega]

In lecture, Lavelle gave us a diagram where if the pH was < pKa, it would be acidic and if it was > pKa, it would be basic. What is pKa in this diagram? Is it a number that we need to memorize?

[Jessy Ji 2J]

Hi,

pKa is the negative log base ten of the Ka value, which is the acid dissociation constant. So pKa tells you how strong an acid is. I don't think you need to memorize any number for that.

[Grace Chen 3F]

pKa is an indication of how acidic an acid is. pKa = -log Ka, and the smaller the pKa of an acid, the stronger the acid is. I don't think we need to memorize the values of pKa for each acid.

[Hanyi Jia 3B]

The reason we take pKa, -log (Ka), is to have a direct comparison with pH on a logarithm basis.
Here is how it works:
If pH > pKa
then, [H₃O⁺] < Ka
We know that Ka is an equilibrium constant that equal to [H₃O⁺] [A^-]/[HA]
So, [H₃O⁺] < [H₃O⁺] [A^-]/[HA]
This means [A^-] > [HA].
Now you can say acid tends to deprotonate because the reaction leans to the product side.
Essentially this means that the pH of this solution is high, not many [H₃O⁺] is there, so the acid tends to deprotonate (until reaching eq again).

The same is true for pKb.

Hope this helps, and please correct me if I am wrong.

[michaelcrisera]

pKa is an indication of how acidic an acid is. pKa is the negative log of an equation's equilibrium constant, Ka, which provides a value representing which side of a dissociation equation will be favored. If an equation has a high Ka, it will have a low pKa, and a low Ka will result in a high pKa.

[905767718]

Ka is the equilibrium constant of an acid -> this means that the value (ranges from 0 to 14) is what the pH of the solution will have to be for the acid to be neutralized. An example of how to understand this:

Ka (equilibrium constant) = 4
pH = 5

Based on the information in this problem we know that when the pH of the solution is 4, the acid will be neutralized. If the pH of the solution is lower than 4 (0 - 3.9), then the solution is more acidic than the acid itself. However, based on this example the pH is less acidic than the acid so the acid will start to dissociate.

pKa is the negative log (-log) of Ka and it gives you the concentration of H3O+ ions in the solution. This is an indicator for how acidic the solution is because acids lose protons and create H3O+ ions. The more hydronium ions there are, the more acidic something is.