CHEMISTRY: ART, SCIENCE, FUN

PRACTICALEXAMINATIONANSWER SHEETSJULY 18, 2007
MOSCOW, RUSSIA
Official English version

Problem1

Name: _______________

Quest.

1a 1b 1c2-3

4Tot

PointsStudent code: _________

Marks

972

286

2003

Number of the given mixture of amino acids ________ (A number between 301 and 600)
1.1a Draw the profile of coloration intensity on the plate sketch.
1.1b Indicate changes of eluents by drawing lines between the corresponding wells.
123456789101112ABCDEFGH
1.1c Labels of wells corresponding to the chosen fractions.
Peak number
Labels of wells
123
1.2-1.3 Content (in mg) of each amino acid in the amino acid mixture you were given.
Your work

Official English version

Problem1

Name: _______________

Quest.

1a 1b 1c2-3

4TotPoints

Student code: _________

Marks

972

286

20

Complete the table.
PeakVolume ofnumber
combined
fractions, mL
12
3Amino acid(3-lettercode)0

Wavelengthλ, nm

3AbsorbanceAλAmino acid mass inthe given mixture,mg

ATTENTION. The print-offs with the spectra of your samples should be put into theenvelope and delivered at the end of examination alongside with the Answer Sheets.
1.4 Resonance structures of the substance responsible for the mixture coloration.

Official English version

Problem
2

Name: _______________

Quest.

Student code: _________

Marks 25

2.1a Standardization of NaOH solution
Titration No Initial burette reading,mL
12
3

1a 1b523456a 6bTot

Points2525

55

110020

Final burette reading,mL

9Volume of NaOH solution
consumed (V1), mL

Final volume of NaOH solution (V1,f), mL
2.1b Calculation of NaOH concentration
Your work

с(NaOH) = __________ mol/L

2.2 The first titration of the sample (BCG)
Titration No Initial burette reading,Final burette reading,
mL
mL
1
2
3

Volume of NaOH solution
consumed (V2), mL

Final volume of NaOH solution (V2,f), mL
2.3 The second titration of the sample (TP)
Titration No Initial burette reading,Final burette reading,Volume of NaOH solution
mLmL
consumed (V3), mL
123
Final volume of NaOH solution (V3,f), mL
2.4 Calculation of the mass of CO32Your workm(CO32-) = __________ g
Official English version

Problem
2

Name: _______________

Quest.

1a 1bStudent code: _________

Marks 25523

4

56a 6bTotPoints

25

25

55

1100

20

92.5 Calculation of the mass of HPO42Your workm(HPO42-) = __________ g
Additional questions
2.6a Indicate one reaction (write down the equation) for a process interfering in the sample
analysis you have carried out in the presence of Ca2+.

2.6b A list of mistakes possible at different steps is given in the table. Indicate which of themistakes can lead to errors in CO32- and/or HPO42- content determination. Use the following
symbols: “0” if no error is expected, “+”or “–“ if the result is higher (positive error) or lower(negative error) than the true one.
Error
StepMistake
2CO3 content
HPO42- content
Incomplete removal of CO2
1
Too large excess of K2C2O4 on calcium precipitation
2Too late indication of the endpoint (overtitration) on
3
NaOH standardization
Insufficient washing of the filter at CaC2O4 filtration
4
Overtitration of the sample against BCG
5
Overtitration of the sample against TP
6
H2CO3:
pKa1 = 6.35; pKa2 = 10.32
H2C2O4:
pKa1 = 1.25; pKa2 = 4.27
Extra samples given or column broken
Problem NoSample NoColumn broken
and replaced

Student’s signature

Lab assistant’s signature

Official English version