Does pKa drop as temperature goes up?

[69ron]

Does pKa vary as the temperature goes up?

SWIM was freebasing an alkaloid in water at ROOM TEMPERATURE. Today was an extra hot day. The alkaloid freebased at 1 pH point lower than it normally does. SWIM was baffled at first. He did it over and over just to make sure everything was done according to procedure. The procedure used was not altered in any way at all, and has been performed dozens of times with the same results until today. It’s about 20 C hotter than it usually is. He performs the freebasing at room temperature, so the water is 20 C hotter than it has been pretty much all the other times he’s freebased the alkaloid.

So, the only thing that changed is the room temperature so the water is approximately 20 C hotter than it’s been in the past. Does this alter the pKa of an alkaloid making it freebase at a lower pH? SWIM’s pH meter is perfectly calibrated. He’s using the same amount of water, the same amount of base, the same amount of alkaloid, etc., only today it freebased 1 pH point lower. Is the hot weather doing this?

 

[SpasticSpaz]

Yep, pKa can vary with temperature.

pKa is a function of the equilibrium constant for the acid's disassociation. Thus, by Le Chatelier's principal, if the disassociation is endothermic, then raising the temperature will decrease the pH required to freebase a given percentage of the alkaloid salt.

 

[prottel]

What alkaloid were you working with 69ron?

Could anyone explain more thourougly the relation between pka and temperature?

 

[kemist]

What alkaloid were you working with 69ron?

Could anyone explain more thourougly the relation between pka and temperature?

That`s actually very good question. have to search some books and find out how to determine this:roll: if it`s possible :?

 

[kemist]

hey dagger didn`t you write this before???

What alkaloid were you working with 69ron? If you need ph 7.7 to freebase 50% harmine at 25C, what ph would freebase 50% at 100C?

cos when I quoted it changed to this

What alkaloid were you working with 69ron?

Could anyone explain more thourougly the relation between pka and temperature?

What the heck :shock:

 

[prottel]

haha. Yeah, I posted that first quote, but changed it within a minute, because I thought none probably knew the answer to it. You read the post before I had the time to change it

 

[kemist]

haha. Yeah, I posted that first quote, but changed it within a minute, because I thought none probably knew the answer to it. You read the post before I had the time to change it

GOTCHya doggy dagger! :lol: :lol: :lol:

 

[burnt]

The relation to pka and temperature is similar to the relationship between pH and temperature. There are equations to estimate these changes. Consult a chemistry text.