Download che 3221-analytical chemistry ii - UR-CST

Reg. No:…………………………….
KIGALI INSTITUTE OF SCIENCE AND TECHNOLOGY
INSTITUT DES SCIENCES ET TECHNOLOGIE
Avenue de l'Armée, B.P. 3900 Kigali, Rwanda
INSTITUTE EXAMINATIONS – ACADEMIC YEAR 2012/2013
END OF SEMESTER II SUPPLEMENTARY EXAMINATION
FACULTY OF SCIENCE
SCIENCE 4-CHEMISTRY
SECOND YEAR, EXAM SEM. II
CHE 3221-ANALYTICAL CHEMISTRY II
DATE: 28/06/2013
TIME: 2 HOURS
MAXIMUM MARKS = 60
INSTRUCTIONS
1. This paper contains TWO sections
2. Answer Question ONE in section A, and any TWO out of the THREE
Questions in section B
3. No written materials allowed.
4. Write all answers in the booklet provided.
5. Do not forget to write your Registration Number.
6. Do not write any answers on this question paper
Section A
1.
a. If the absolute uncertainty in reading a buret is constant at ±0.02 mL, what will be the
percent relative uncertainty: (a) for a volume of 15 mL, (b) for a volume of 0.085 L.
(4 marks)
b. With a schematic diagram, explain how Gravimetric combustion analysis for carbon and
hydrogen is achieved
(6 marks)
c. How might the number of theoretical plates in a chromatographic column be determined?
(2 marks)
d. State classification of analytical methods by filling the following table with required
information:
(4 marks)
Name of the method
Basic principle
Electroanalytical methods
Determination of the mass of the analyte or some compound related to it.
Titrimetric methods
based on measurement of the interaction between electromagnetic
radiation and analyte
e. Calculate the concentration of Pb2+ in a solution that was prepared by mixing 22.0 ml of
0.0300 M Pb2+ and 15.0 ml of 0.0440 M EDTA. The mixture was buffered at pH of 7.75
(look for constants at the end of this questionnaire)
(4 marks)
Section B
2.
a. State four desirable properties of a gravimetric precipitate
(2 marks)
b. Why is high relative supersaturation undesirable in a gravimetric precipitation? (2 marks)
c. Consider the following arithmetic calculation and determine the absolute uncertainty
accompanying the answer:
(3 marks)
d. Describe systematic error citing a relevant example
(2 marks)
e. Explain why in iodometry method of analysis iodine is normally used in a solution
containing excess I–? Show the reaction occurring in that solution
(2 marks)
f. Citing a specific example explain the precipitation from homogeneous solution (3 marks)
g. To find the Ce4+ content of a solid, 4.37 g were dissolved and treated with excess iodate
to precipitate Ce(IO3)4. The precipitate was collected, washed well, dried, and ignited to
produce 0.104 g of CeO2 (FM 172.114). What was the weight percent of Ce (FM 140.1)
in the original solid?
(6 marks)
3.
a. In Potentiometric Titration, iron(II) ions (Fe2+) concentration is determined by
permanganometry explain briefly this technique giving the balanced reaction involved
(4 marks)
b. With the Aid of a sketch, explain the Standard Hydrogen Electrode (S.H.E)
c. 0.649-g sample containing K2SO4 (FM 174.27) and Al2(SO4)3
(3 marks)
(FM 342.15) was
dissolved in water and treated with Ba(NO3)2 to precipitate all sulfate as BaSO4 (FM
233.39). We want to know the percent weight of K2SO4 in the sample if 0.977 g of
precipitate was formed.
i.
Write 2 equations necessary to solve this problem
(3 marks)
ii.
Calculate % K2SO4in the sample
(6 marks)
d. Marie Curie dissolved 0.091 92 g of RaCl2 and treated it with excess AgNO3 to
precipitate 0.088 90 g of AgCl. In her time (1900), the atomic mass of Ag was known to
be 107.8 and that of Cl was 35.4. From these values, find the atomic mass of Ra that
Marie Curie would have calculated.
(4 marks)
4.
a. Why Ethylene
Diamine tetraacetic Acid (EDTA) is the most and widely utilized
chelating agent
(3 marks)
b. One of the indicators for titrations using EDTA is Eriochrome Black T. Give its chemical
formula and show its color before and after equivalence
(2 marks)
c. During a titration of 30.0 ml of a palladium (II) solution, 15 mL of 0.020M EDTA is used
to reach the end –point in a solution buffered to constant pH= 11 (α4 = 0.846)
i.
Determine 3 preequivalence-point values for pPd (at 0 mL ; 6 mL and 12 mL of
EDTA added)
(3 marks)
ii.
Calculate the pPd at equivalence- point
(3 marks)
iii.
Determine 3 postequivalence-point values for pPd (at 16 mL; 18mL and 22mL of
iv.
EDTA added)
(6 marks)
Derive the curve of this titration
(3 marks)
EDTA constants: K1, K2, K3, K4 are respectively 1.02 x 10-2, 2.14 x 10-3, 6.92 x 10-7, 5.50 x 10-11