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Chem Istry For Agriculture Question Paper
Chem Istry For Agriculture
Course: Bachelor Of Agriculture In Agricultural Extension And Rural Development
Institution: Pwani University question papers
Exam Year:2012
1
A Constituent College of Kenyatta University
UNIVERSITY EXAMINATIONS 2010/2011 ACADEMIC YEAR
1
ST
YEAR 1
ST
SEMESTER EXAMINATION FOR THE
DEGREE
OF
BACHELOR OF SCIENCE IN AGRICULTURE & ENTERPRISE
DEVELOPMENT
AST 104
:
CHEM
ISTRY FOR AGRICULTURE
END SEMETER: I
TIME: 3 HOURS
DAY/TIME:
Answer all questions in section A and any two in section B
SECTION A (40 marks)
CO
2
= 44.010,
C=12.011, H=1.008,Na
2
S
2
O
4
=174.1, K
w
= 1.0× 10
-
14
, Mg(OH)
2
= 58.32, NaHCO
3
= 84.01
1.
Name the following compounds
:
ClO
2
, HIO
4
and Ca(H
2
P0
4
)
2
(
3 marks
)
2.
Write the formula of the following compounds:
Calcium hypochlorite, ammonium chromate and bromic acid
(
3 marks
)
3.
Vitamin C is essential for the prevention of scurvy. Combustion of a 0.200 g
sample compound yields 0.2998 g CO
2
and 0.0819 g H
2
O. What is the empirical
formula of vitamin C?
(
4 marks
)
4.
Calculate the pH of a 5.0 × 10
-
2
M NaOH solution.
(
2 marks
)
5.
The standard molar enthalpies of combustion of C
2
H
2
(g), C(graphite) and H
2
are
-
1299.63,
-
393.51,
-
285.85 KJ mol
-
1
respectively. Calculate the standard enthalpy
of formation of C
2
H
2
(g).
(
4 marks
)
2
6.
The reaction below is used to determine th
e sulfite ion concentration present in
freshwater from a papermaking plant.
SO
3
2
-
(aq) + MnO
4
-
(aq)
SO
4
2
-
(aq) + Mn
2+
(aq)
(a)
Balance the half equations of the reaction
(
3 marks
)
(b)
Write the overall reaction
(
2 mark
s
)
7.
Predict whether a reaction will occur in each of the following cases and if so write
a net ionic equation for the reaction.
(a)
BaS(aq) + CuSO
4
(aq)
(
2 marks
)
(b)
(NH
4
)
2
SO
4
(aq) + ZnCl
2
(aq)
(
2 marks
)
8.
Write the structure of 4
-
t
-
butyl
-
2
-
methylheptane.
(
3 marks
)
9.
Baking soda (NaHCO
3
) is often used as an antacid and neutralizes excess
hydrochloric acid secreted by the stomach. Milk of magnesia, which is an aqueous
suspension of magnesium hydroxide, is also used as an antacid.
(a)
Write equations for the neut
ralization reactions of the baking soda and of milk
of magnesia.
(
2 marks
)
(b)
Which is the more effective antacid of the two?
(
3 marks
)
10.
Draw the Lewis structures of PH
3
and predict its shape consistent with its
hybridization.
(
3 marks
)
11.
Writ
e the mechanism for the photolytic chlorination of methane.
(
4 marks
)
SECTION B
Answer any two of the following three questions
12.
Sodium dithionate, Na
2
S
2
O
4
is an important reducing agent in wastewater
management. One interesting use is the reduction of chr
omate ion to insoluble
chromium (III) hydroxide by dithionate ion S
2
O
4
2
-
, in basic solution with sulfite
ion as yet another product. During routine chemical inspection chromate ion was
found to be present in the wastewater from a chromium plating plant. Wr
ite the
ionic expression for the reaction.
(a)
Write balanced equations for the redox reaction showing clearly the species
undergoing reduction and those that are oxidized.
(
3 marks
)
(b)
Combine the half equations in (b) to obtain the overall equation.
(
5
marks
)
(c)
Write the overall equation for the redox reaction in basic conditions.
(
3 marks
)
(d)
What mass of Na
2
S
2
O
4
is consumed in a reaction with 100.0 L of wastewater
having CrO
4
2
-
= 0.0148 M?
(
4 marks
)
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