Chemistry Reference
In-Depth Information
Problems
(a)
Ethanolamine (HOCH
2
CH
2
NH
2
, relative molecular mass
Q1.1
61.08) has a p
K
a
of 9.4. Explain what this term means.
(b)
Explain why ethanolamine is freely soluble in water, and
why the resulting solution is basic.
(c)
Calculate the pH of a 1% w/v solution of ethanolamine.
(d)
A solution of pH 9.0 is required that will resist changes in
pH on the addition of small amounts of strong acid or
strong base. Indicate briefly a possible composition of such
a solution, and show how pH changes are resisted.
(a)
What do you understand by the term p
K
a
? Explain how this
value can be used to indicate the strength of a base.
Q1.2
(b)
The base ephedrine has a p
K
a
value of 9.6. Calculate the
theoretical end point pH when a 0.1
M
solution of ephedrine
is titrated with 0.1
M
HCl.
(c)
Acetic acid (CH
3
COOH) has a p
K
a
value of 4.76. How
might you prepare an acetate buffer with a pH of
5.0,
containing 0.1 mol L
1
of the acid?
(d)
Calculate the buffer capacity of
the solution described
above.
Describe the ionisation or ionisations that occur when fully
protonated lysine (Figure 1.10) is subjected to increasing pH.
What is the dominant structure present at the isoelectric point?
Q1.3
COOH
H
C
H
2
N
NH
2
Figure 1.10
The structure of lysine.
(Answers to problems can be found on pp. 251
253.)
