Posted by Meenaakshi on .
Arrange these acids in terms of increasing acidity:
CH3COOH, NH3+CH2COOH, CH3CONHCH2COOH
Dr.Bob asked me what NH3+CH2COOH is.NH3+CH2COOH is obtained when 1 mol of glycine is added with a very strong acid,which results in both the amino & carboxyl groups to be fully protonated.
pKa of NH3+CH2COOH is 2.35
OK. Thanks. Here is what I didn't like about your "formula". This is an amino acid (as you noted) BUT I don't think you should write it as NH3 + CH2COOH because there is no such compound as CH2COOH. I just assumed you had made a typo that first time around. I think glycine should be written as H2NCH2COOH and the protonated amino group then would be shown as +H3NCH2COOH. That makes a lot more sense to me. So we are comparing this acid with a pKa of 2.35 with acetic acid with pKa of 4.74 and this is of course stronger. I don't remember the other compound that was to be ranked. If you have the pKa for that one, too, you know where it goes.
Thank you Dr.Bob & sorry for the inconvenience caused to you