[Joules23]

i dont understand this question... i know the iso-electric point is at its middle pKa(9), so this would also be the target pH too.. but wouldnt the fully protonated form of Lysine be at the the lowest pH and pKa... and wouldnt HCl lower the pH

[GeoffG]

i dont understand this question... i know the iso-electric point is at its middle pKa(9), so this would also be the target pH too.. but wouldnt the fully protonated form of Lysine be at the the lowest pH and pKa... and wouldnt HCl lower the pH

The isoelectric point is an average of all the pKas. 9 is not the pI.

[Joules23]

The isoelectric point is an average of all the pKas. 9 is not the pI.

Not quite.. Your right pI is not 9.. but its not the average of all 3 pKa's.. is the average of the two pKa's involved in the deprotonation to get Lysine to a neutral state.. so pI is (9+11)/2 =10 . but still, im not understanding how the question asks how many mol of HCl needed.. because in its most protonated form Lysine is at a low pH (much lower than the pI pH10).. adding HCl will lower the pH more, right?

[Borek]

Obviously something is wrong with the question.