quick question about pKa values

[steppingstone]

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Question about pKa values...the smaller the pKa, the more acidic or is it the opposite?

This is in reference to question 26 in destroyer 2012. It asks which proton has the SMALLEST pKa value...and the answer states it is the H on the carboxy acid.

 

[patricklin27]

the smaller the pKa value, the more likely a proton will dissociate and as a result the stronger the acid.

once the pH reaches past the pKa, the hydrogen will be dissociated. Since the pKa is small, it will be easier for the molecule's pH to reach past the pKa value, thus being easier for the proton to be dissociated.

 

[nirjar2212]

Question about pKa values...the smaller the pKa, the more acidic or is it the opposite?

This is in reference to question 26 in destroyer 2012. It asks which proton has the SMALLEST pKa value...and the answer states it is the H on the carboxy acid.

In layman's term, think of pKa =pH... Should get you right answer almost all the time.

Sent from my SAMSUNG-SGH-I747 using Tapatalk

 

[ekephant]

Yes lower pKa values are stronger acids. If I ever forget I just remembered that a higher Ka is a stronger acid, and pKa = -log(Ka). Therefore a high Ka = low pKa = stronger acid. Kind of confusing at first, but once you understand it you won't forget.

 

[steppingstone]

ahh thank you very much everyone!!

 

[free99]

Yes lower pKa values are stronger acids. If I ever forget I just remembered that a higher Ka is a stronger acid, and pKa = -log(Ka). Therefore a high Ka = low pKa = stronger acid. Kind of confusing at first, but once you understand it you won't forget.

Good advice. You can keep track of what Ka values mean if you remember the dissociation equation Ka=[H+][A-]/[HA]. Therefore, if you have a big Ka, the numerator is large or the denominator is small, meaning much of the acid is dissociated.

 

[Dhooy7]

So strong acids are good at donating electrons. However, I have low pKas as well would be best to donate protons. I am trying to understand this becuase I think it should say high pKas (stronger acids)

 

[mw18]

So strong acids are good at donating electrons. However, I have low pKas as well would be best to donate protons. I am trying to understand this becuase I think it should say high pKas (stronger acids)

High Ka, not pKA. Low pKa and low pH are the more acidic. Something with a high Ka dissociates more easily, making it a stronger acid. Something with a high Ka will have a low pKa.