2014 paper 3 qn 4c
We are asked to draw the predominant species of amino acids at
ph7 ,
And given by the qn phenol side chain is negligible at
pH7
Valine : one acid and amine group
Tyrosine : 1 co2h , 1 nh2 group
Aspartic acid : 2 co2h group, 1 nh2 group
From cs toh book,
The pH at which an amino acid has a net charge of zero is the
isoelectric point.
{Amino acids with one co2h group and one nh2 group have
isoelectric points in the ph range 5.5-6.5}
Do we have to memorise the one above^ {in brackets}
We know pH lower than pka, compound protonates
pH greater than pka, compound deprotonates
We aren't given the pka of the functional groups in this qn
Are we supposed to memorise the pka of co2h and nh2 groups?
Or we see ph 7 just draw every acidic group deprotonate and
every basic group protonate?
-Is it like oh,
ph7, its like water, every acidic group and basic group ionises in
water (does it?)
Can ask chemistry
questions here after 2015 chem a level papers and would u continue
to reply?
If Cambridge gives you the pKa of the amino acid's R group, use it
to determine if at a particular pH, the R group is protonated or
deprotonated. And as you say, "ph 7 just draw every acidic group
deprotonated and every basic group protonated". That's right.
Because after 2015 A levels, you might retake your A levels in
2016? Or some other reason?