# Question #5f0d2

Jan 27, 2015

At pH 12, all the acidic hydrogens will have been removed.

We usually write the structure of lysine as

In very acidic solutions (pH 1), both NH₂ groups will be protonated, as in structure A below.

The $\text{p"K_"a}$ values are:

COOH = 2.2
NH₂ = 9.0
NH₂ in side chain = 10.5

As you make the solution more basic, you will remove the acidic protons one after the other.

By the time you reach pH 12, you will have removed all of the acidic protons.

Lysine will exist as structure D.