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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: dun13203171 on November 12, 2015, 02:16:05 PM

Title: How to know if a molecule will be ionised or not in solution at a certain pH?
Post by: dun13203171 on November 12, 2015, 02:16:05 PM

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For instance I have been given a question asking if this molecule was in solution at ph7 would it exist perdominatly as neutral molecules, cations, anions, unionised molecules or amphoteric with only one answer being correct.

Without a pKa value, how do you know if the amide will predominatly accept a proton to adopt a + charge.

If someone could help explain this to me that would be great.

Title: Re: How to know if a molecule will be ionised or not in solution at a certain pH?
Post by: kriggy on November 12, 2015, 03:57:31 PM

1) its not an amide but amine, slight difference in rethorics but huge difference in chemistry of the compound
2) if you know that it is an amine, what are generaly, acido-basic properties of amines?

Title: Re: How to know if a molecule will be ionised or not in solution at a certain pH?
Post by: dun13203171 on November 17, 2015, 08:02:03 PM

It has a lone pair of electrons on the nitrogen, so can act as a base by accepting a proton, those being ionised due to a plus charge.

What I am unsure about is looking at say 5 molecules, all with different functional groups and being able to determine which are easily ionised, not at specific pH's but just in general.

Should you go by pKa values?