Physical Chemistry Laboratory (CHMS2205)
BSc, Chemistry - CHMS
Semester: Second Semester
Level: 200
Year: 2016
REPUBLIC OF CAMEROON THE UNIVERSITY OF BAMENDA
Peace-Work-Fatherland
P. O. BOX 39 Bambili
School/Faculty:SCIENCE Department:_CHEMISTRY Lecturer(s): NDIKONTAR/NONO___
Course Code: _CHMS2205____Course Title: PHYSICAL CHEMISTRY LABORATORY
Date: _08-07-2016_______Halls: __ PBA08________TIME: 14:30-16:30
Instructions: Answer all questions.
Before starting to answer the questions, fill in the header of the answer sheet as required.
Question 1 (12 marks)
In a separatory funnel, a volume V
1
= 100 mL of an aqueous solution of iodine C
1
= 0.Q01 M is mixed with a
volume V
2
= 10.0 mL of pure tetrachloromethane CCI
4
. The mixture is vigorously shaken for 5 minutes and then left
to rest for 15 minutes. Since the two solvents are not miscible, two phases are formed with the lower phase being the
organic. Iodine has distributed itself into the two phases according to the equation:
equation
A volume V
3
= 20 mL of the aqueous phase is taken out of the mixture and titrated using V
4
= 4.4 mL of a C
4
=
0.001 M solution of sodium thiosulphate Na
2
S
2
O
3
(in the presence of an appropriate indicator).
1) Write down the equation for the titration reaction given that the two redox couples involved are I
2
/I
-
and S
2
O
6
2-
/
S
2
O
3
2-
. (2 marks)
2) Which is the appropriate indicator for this titration? Indicate the colour change at the end point. (2 marks)
3) Calculate the concentration of the iodine solution titrated C
3
. (2 marks)
4) Deduce from this, the amount x (mol) of iodine in the organic phase. (2 marks)
5) K is the partition coefficient of iodine in the reaction above. Define it. (1 mark)
6) Express K as a function of C
1
, V
1
and x. Calculate its value (hint: express the n° of moles at t
o
and at t
eq
). (4
marks)
Question 2 (10 marks)
In the laboratory, you were given an aqueous solution of sodium chloride of unknown concentration and all that is
necessary to determine it.
a) From the work that you carried out in the laboratory during this course, propose the name of a method you
used to determine the unknown concentration. (1 (mark)
b) What equipment (instruments and reagents) did you need to carry out this determination? (2 marks)
c) Describe fully the procedure that you used to carry out this determination. (5 marks)
d) Why do you think that your method was better (of not) compared to the other one? (2 marks)
Question 3 (13 pts)
During the experiment to calibrate some laboratory glassware, a buret, a pipet and a measuring flask were used.
I. Explain the meaning of calibration and say why glassware needs to be calibrated (1 pts)
II. Which of the instruments used in the experiment need to be absolutely dry and why? (1 pts)
III. During a session, Anyere obtained the following results with the burette:
volume of water added to beaker (mL) mass of beaker and water added (g)
0
51.82
5.0 56.70
10.0 61.69
20.0
71.66
30.0 79.20
40.0
91.70
50.0 101.92
www.schoolfaqs.net
i. Why is the mass of water measured on the balance referred to as the apparent mass (AM) in this
experiment? (1 mark)
ii. Develop the formula for calculating the real mass (RM) of water using the apparent mass(3 marks)
iii. Given that the density of air is 0.0012 g/mL that of water at 26*C 0.9968 g/mL and that of brass 8.4
g/mL, make a table with the following columns using Anyere's data (4 pts):
AV (mL)
(1 decimal)
AM(g)
(2decimals)
RM(g)
(2 decimals)
RV (mL)
(1 decimal)
AV (mL)
(1 decimal)
5.0
10.0
…
…
…
…
iv. Draw a graph of RV = f(AV), determine its gradient and comment on the result (4 pts)
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