Analytical Methods in Chemistry (CHMS3104)
BSc, Chemistry - CHMS
Semester: First Semester
Level: 300
Year: 2018
UNIVERSITY OF BAMENDA FACULTY OF SCIENCE
END OF SEMESTER EXAMINATION 2017/2018
DEPARTMENT: CHEMISTRY COURSE INSTRUCTOR: NFOR E. Ngwang.
MONTH: MARCH COURSE CODE & NUMBER: CHMS 3104
YEAR: 2018 COURSE TITLE: ANALYTICAL&INSTRUMENTAL METHODS
DATE: 5
th
March 2018 TIME: 11.00-114.00
TIME ALLOWED: 3HOURS CREDIT VALUE: 6
INSTRUCTIONS: ANSWER ALL QUESTIONS IN AN ORDERLY MANNER. You must show your calculations,
including equations and proper units on a question to obtain any mark.
Ql(a) Calculate the equivalent weight and normality for a solution of 6.0 M H
3
P0
4
given the following
reactions:
(i) H
3
P0
4
(aq) + 30H
-
(aq) = P0
4
3-
(aq) + 3H
2
0(l)
(ii) H
3
P0
4
(aq) + 2NH
3
(aq) = HP0
4
2-
(aq) + 2NH
4
+
(aq)
(iii) H
3
P0
4
(aq) + F
-
(aq) = H
2
P0
4
-
(aq) + HF(aq) 3marks
(b) Commercial HC1 is labelled 37% m/m with density of 1.1 8g/rnL. Find
(i) Molarity of HC1
(ii) Mass of solution containing 0.1 mol of HCl.
(iii) Volume of solution containing 0.1 mole of HC1.6marks
(c) A concentrated solution of aqueous ammonia is 28.0% w/w NH
3
and has a density of 0.899 g/mL.
What is the molar concentration of NH
3
in this solution?2marks
Q2(a)By the used of equations only explain the salient features of Kjeldahl method of analysis. 4marks
(b) How and why has the conventional Kjeldahl method of analysis been modified? 3marks (c) The amount
of protein in a sample of cheese is determined by a Kjeldahl analysis for nitrogen. After digesting a
0.9814-g sample of cheese, the nitrogen is oxidized to NH
4
+
, converted to NH
3
with NaOH, and distilled
into a collection flask containing 50.00 mL of 0.1047 M HCl. The excess HCl is then back titrated with
0.1183 M NaOH, requiring 22.84 mL to reach the bromothymol blue end point. Report the %w/w protein in
the cheese given that there is 6.38 g of protein for every gram of nitrogen in most dairy products. 6marks
(d) Briefly explain the difference between a Fajans and Volhard’s titration. 3marks
Q3(a) A sample has a percent transmittance of 50%, What is its absorbance? 2marks (b) A 5.00 x 10
-4
M
solution of an analyte is placed in a sample cell that has a path length of 1.00 cm. When measured at a
wavelength of 490 nm, the absorbance of the solution is found to be 0.338. What is the analyte’s molar
absorptivity at this wavelength? 3marks
Q4 (a) Calcium content of a mineral was analysed five times by each of two methods. Are the mean values
significantly different at the 95% confidence level? 6 marks
www.schoolfaqs.net
Method Ca (wt%)
1 0.02.71 0.0282 0.0279 0.0271 0.0275
2 0.02710.0268 0.0263 0.0274 0.0269
(b) Define the following: (i) precision (ii) indeterminate error (iii) Buffer
(iv) Equivalence point. 4marks
(c) What are the conditions a reaction must fulfilled for use in titrimetric analysis? 4marks
Q5. (a) Name two types of electrical cells define them. (4 points)
(b). You are given the following cell (10 points)
Zn(s) | Zn
2+
(aq , 0.0100 M) || Ag
+
(aq, 1.15 M) | Ag(s)
Zn
2+
(aq) + 2e Zn(s) E° = - 0.76 V
Ag+(aq) + e Ag(s) E° = 0.80 V
i. Which species is oxidized when current is allowed to pass through the cell?
ii. Which species is reduced when current is allowed to pass through the cell?
iii. What is the value of
E
0
cell
?
iv. Which electrode is the anode?
v. In which direction do electrons flow in the external circuit?
vi. How many electrodes are transferred in the balanced equation?
vii. What is the value of Q, the reaction quotient for the cell?
viii. What is the cell potential at 25 °C?
ix. What is the value of the equilibrium constant at 25 °C for the reaction?
(c) You are given the following cell: (10 points)
IO
+ 5c l/2I
2
(s) + 3H
2
0 E° - 1.195 V
Br
2
(I) +2e ⇆ 2Br E° = 1.087 V
Calculate E° and K
eqm
for the following reaction.
I
2
(s) + 5Br
2
(aq) + 6H
2
0 ⇆ 2IO
+
12H
+
+ 10Br
-
,
USEFUL DATA YOU MAY REQUIRE
Values of t for at 95% confidence level for various degree of freedom
Degree of Freedom Factor for confidence Interval %
1
12.7
2
4.30
3
3.18
4
2.78
5
2.57
6
2.45
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