Question

glycine and lysine, have the following values of the relevant acid dissociation constants (pKa)
glycine, pKa=2.35
lysine,pKa=10.79

For an aqueous solution of glycine alone, calculate the value of pH at which the ratio of the concentration of neutral glycine zwitterions to the concentration of protonated cation is 102.

Answer 1

This tutorial may help.
http://www.chem.uiuc.edu/CLCtutorials/104/AminoAcidTitrations/SeeIt.html
I would use the Henderson-Hasselbalch equation and substitute into the log term either 1/100 or 100/1 depending upon which way you want to write it.

Answer 2

Here is the titration curve for glycine.
https://www.google.com/search?q=titration+amino+acids&client=firefox-a&hs=ha9&rls=org.mozilla:en-US:official&channel=sb&tbm=isch&tbo=u&source=univ&sa=X&ei=jjr9U9jcKdH9yQTljIH4Dw&ved=0CCYQsAQ&biw=1024&bih=609#facrc=_&imgdii=_&imgrc=HsTtE2YEggYW1M%253A%3BEMsM7v-IV9G1fM%3Bhttp%253A%252F%252Fwww.chem.fsu.edu%252Fchemlab%252Fbch4053l%252Fcharacter%252Ftitration%252Findex_clip_image006.jpg%3Bhttp%253A%252F%252Fwww.chem.fsu.edu%252Fchemlab%252Fbch4053l%252Fcharacter%252Ftitration%252F%3B369%3B275

Answer 3

thank you I'm looking into this albeit totally lost atm

Answer 4

9.78+log10(1/102)
=7.77

sounds good?

Answer 5

Nevermind, I did it, I should be paying you for all this help ;)

I had to take other pk

2.35+log10(102)
=4.35

Answer 6

4.35 is correct