pH to pKa?

[pandalove89]

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Okay for some reason I can't find a fast way to convert pH to pKa...


On question #178 on the 2011 DAT destroyer in the GCHEM section I was getting stuck because o this.


If the pH is 9 how could you easily calculate the pKa (should be around 4.4)?

 

[PooyaH]

You're not understanding the question right. The question is not asking you to figure out the pKa. The main point of this question is for you to distinguish between when a solution is protonated or deprotonated. When the pH is 9, it is most likely deprotonated since it's basic. All of the choices are giving you the protonated color except d, which is the deprotonated color of sample D.

This question might seem very complicated at first, but it's actually pretty simple if you know what it's asking.

 

[pandalove89]

You're not understanding the question right. The question is not asking you to figure out the pKa. The main point of this question is for you to distinguish between when a solution is protonated or deprotonated. When the pH is 9, it is most likely deprotonated since it's basic. All of the choices are giving you the protonated color except d, which is the deprotonated color of sample D.

This question might seem very complicated at first, but it's actually pretty simple if you know what it's asking.

Oh I see. So the pKa of the aqueous solution doesn't have to do with anything?

Also just for my future reference, is there a way to convert pH to pKa easily?

 

[pandalove89]

bump

 

[Demps]

Oh I see. So the pKa of the aqueous solution doesn't have to do with anything?

Also just for my future reference, is there a way to convert pH to pKa easily?

I have never encountered a question that requires pH to pKa conversion so I wouldn't worry about it. pH and pKa are just used as a reference one from the other relatively to see whether the electronegative atom is ionized or not.

 

[needzmoar]

Oh I see. So the pKa of the aqueous solution doesn't have to do with anything?

Also just for my future reference, is there a way to convert pH to pKa easily?

Converting pH to pKa without additional information? No

 

[MuskieMan33]

Maybe with a pH vs. NaOH titration curve or graph. At least that's what I think about when I think pH to pKa. (probably the weak acid - strong base titration I had to do)