CHEM1907/CHEM1908
2003-J-4
June 2003
 The partial Lewis structure of lactic acid, the molecule that forms in muscle during
exercise, is shown below. Complete the Lewis structure of lactic acid by drawing the
non-bonded electron pairs around the relevant atoms.
Marks
7
2
H H
3
1
O
H C C C
2
H O
O H
H
2
Complete the following table.
Atom
1
2
Geometric arrangement of the
groups around the atom
Hybridisation of atom
C
O
3
C
Name three types of intermolecular interactions expected of lactic acid.
The pKa of lactic acid is 3.08 and the pKb of ammonia is 4.76. Determine whether
products or reactants are favoured in the following equilibrium reaction. Provide a
brief rationale for your answer.
CH3CH(OH)COOH + NH3
CH3CH(OH)CO2 + NH4+
3
CHEM1907/CHEM1908
2003-J-5
June 2003
 One of the causes of acid rain is a reaction occurring in the upper atmosphere between
gaseous NO2 and water to produce nitric acid and gaseous NO. Write a balanced
chemical equation for this reaction.
As part of their school project on acid rain, some high school students collected a
sample of rain (220 mL) and measured the pH value of the solution, reporting the
value as pH = 3.9. Assuming that the rain sample does not contain any acids other
than nitric acid, calculate the volume of gaseous NO2 that would have been consumed
in the upper atmosphere (where temperature = 56 C and pressure = 11.6 kPa) to
produce the sample of rain collected by the students.
ANSWER:
Marks
8
CHEM1907/8
2004-J-2
June 2004
 Some micro-organisms thrive under warm, acidic conditions where sulfuric acid is
produced as a metabolic by-product from the reaction between sulfur (S), water and
oxygen (O2). Write a balanced equation for this reaction.
Calculate the volume of oxygen that is required to react to completion with 0.0655 g
of sulfur at 1.00 atm and 55 C.
ANSWER:
Calculate the pH of the final solution if the reaction is carried out in 20.0 L of water.
Assume that the sulfuric acid fully dissociates.
ANSWER:
Marks
5
CHEM1907/8
2005-J-4
June 2005
 Shown here are the classical and the zwitterionic forms of the amino acid leucine.
3
O
OH
C
2
H2N CH C
1
CH2 O
H3N CH C
CH3
CH3
CH
CH3
CH2
A
O
CH
B CH3
List the types of intermolecular interactions in which each of the indicated sites (A, B
and C) in leucine could be involved.
A
B
C
Provide the requested information for each of the indicated atoms in leucine.
Atom
Geometric arrangement of the
electron pairs around the atom
Hybridisation Geometry/shape of -bonding
of the atom electron pairs around the atom
1
C
2
C
3
O
Given that the pKa of the carboxylic acid group of leucine is 2.32 and the pKb of the
amine group is 4.24, do you expect the classical or the zwitterionic form to predominate
when leucine is dissolved in water? In other words, does the following equilibrium lie to
the right or left? Show your reasoning.
H2N CH(CH2CH(CH3)2) COOH
H3N CH(CH2CH(CH3)2) CO2
Marks
8