Chemistry Reference
In-Depth Information
(d)
The buffer capacity,
b
, is easily calculated. Suppose we add
0.01 mol of strong alkali (e.g. NaOH). The new pH can be
calculated from the Henderson-Hasselbalch equation (1.6):
(
-----------
)
0.1738
0.01
pH
4.76
log
0.09
pH
5.07
The buffer capacity is defined as the number of moles of
strong alkali added divided by change in pH observed.
0.01
b
----
0.07
b
0.14
The fully protonated form of lysine has the structure shown in
Figure 11.1.
A1.3
COOH
H
H
3
+
+
H
3
Figure 11.1
The structure of lysine.
The hydrogen atoms ionise in the following order: the first from
the carboxy group on the a carbon; the second from the NH
3
on
the terminal carbon (the e carbon); and finally the hydrogen from
the NH
3
on the a carbon. The predominant structure at the pI is
the zwitterion, which has the structure shown in Figure 11.2.
COO
-
H
H
2
N
+
H
3
Figure 11.2
The structure of the lysine zwitterion.
