Student Code

AAA-1

Practical Problems"Bonding the World with Chemistry"
49th INTERNATIONAL CHEMISTRY OLYMPIAD
Nakhon Pathom, THAILAND

Practical problems (official English version), 49th IChO 2017, Thailand

1Student Code

AAA-1

General Instructions.
 Pages: This exam contains 36 pages for practical exam tasks (including the answer
sheets). There are a total of 3 Tasks—Task 1A, Task 1B, and Task 2.
 Exam Reading: Students will have 15 minutes to read this exam booklet before starting
the experiments. The official English version of this examination is available on request
only for clarification.
 Exam Time: Students will have a total of 5 hours to complete all practical tasks. Whenplanning your work, note that several steps require 20-30 minutes.
 Start/Stop: Students must begin as soon as the “Start Command” is given and muststop your work immediately when the “Stop Command” is announced.
The supervisor will announce 30 minute notification before the stop command.
Delaying in stopping the task after the “Stop Command” has alreadyannounced by 1 minute will lead to cancellation of your practical exam.
After the “Stop Command” has been given, place your exam papers in yourexam envelope and wait at your lab space. The lab supervisor will come pickup your exam paper and your submitted items as well as check your lab space.

 Safety: You must follow the safety rules given in the IChO regulations. While you arein the laboratory, you must wear laboratory goggle. The prescription safety glasses
may be used if the supervisor approves. You may use gloves provided when handlingchemicals.






If you break the safety rules given in the IChO regulations, you will receive only
ONE WARNING from the laboratory supervisor. Any breaking safety rules
after one warning will result in being dismissed from the laboratory and zeromarks for the entire practical examination.
No eating or drinking allowed in the laboratory.
Safety issue: Pipetting by mouth is strictly forbidden.
Do not hesitate to ask your assistant or lab supervisor if you have any questions
concerning safety issues. Inform your lab supervisor when need to leave thelaboratory for a restroom break or having snacks.

 Working space: You are allowed to work only in the space assigned for you. Sharedspace and shared equipment must be clean after use.
 Chemical Refills/Replaced: Chemicals and labwares, unless noted, are not supposed
to be refilled or replaced. Chemical and labwares will be refilled or replaced without
penalty only for the first incident. Each further incident will result in the deduction of
1 point from your 40 practical exam points.

Practical problems (official English version), 49th IChO 2017, Thailand

2Student CodeAAA-1

 Disposal: Leave all chemicals and labwares on your working space. Chemical waste
must be disposed in the designated waste bottle for each task.
 Answer sheets: All results and answers must be clearly written in the appropriate areaon the answer sheets for grading. Only answers written with pen will be graded.


Write down student code on every page.
Use only the pens provided for you.
Anything written outside the appropriate area on the answer sheets will not be
graded. You may use the backside of the sheets as scratch papers.
For any calculation, use only the calculator provided.

 Stay hydrated throughout the practical exam. Drinks and snacks are provided
outside the laboratory.
 UV spectrophotometer is to be shared between you and another student.
During the first 2 hours, use it when it is free. You need to wait until the other student
finishes. You cannot use the spectrophotometer for more than 1 hour. (Longer than thatyou will be asked to stop to allow the another student to use.)
You can come back to the spectrophotometer if it is free. Organize your work so thatyou do not waste your time waiting.
Time 0900-1000
Slot
Free

1000-1100
Free

1100-1200
L

1200-1300
R

1300-1400
Free

L = student on the left side of the spectrophotometer
R = student on the right side of the spectrophotometer

You have the right to work on the tasks in any order.

Practical problems (official English version), 49th IChO 2017, Thailand

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Student Code

AAA-1

Practical Exam
Task 1A

Practical problems (official English version), 49th IChO 2017, Thailand

4Student CodeAAA-1

Chemicals and Equipment (Task 1A).
I. Chemical and materials (the actual labeling for each is given in bold font)Hazard Statementsa
Instrument check solution, 80 cm3 in a plastic bottle
H301
2.00  10-4 mol dm-3 Methyl orange indicator solution,
30 cm3 in a wide mouth glass bottle
1.00  10-3 mol dm-3 Bromothymol blue indicatorsolution, 30 cm3 in a wide mouth glass bottle
Methyl red indicator solution, 10 cm3 in a wide mouth
glass bottle
1 mol dm-3 HCl, 30 cm3 in a plastic bottle
1 mol dm-3 NaOH, 30 cm3 in a plastic bottle
buffer solution A, 110 cm3 in a plastic bottle
Unknown solution X, 50 cm3 in a plastic bottle
Unknown solution Y, 50 cm3 in a plastic bottle
Unknown solution Z, 50 cm3 in a plastic bottle
aSee page 34 for definition of Health Statements
II. Equipment and labwares
Shared Equipment
UV-Visible spectrophotometer
Personal Labwares
Beaker, 25 cm3
Volumetric flask, 25.00 cm3
Measuring pipette, 2.00 cm3
Measuring cylinder, 10.0 cm3
Pasteur pipette
Rubber bulb for Pasteur pipette
Pipette filler bulb (3-way)
Pipette tray
Test tube (13 x 100 mm)
Test tube rack
Plastic cuvette, optical path length = 1.00 cm
Waste bottle, 1 dm3
Sticker label set in a zipped bag

H225-H319-H371
H290-H314-H335
H290-H314

Quantity
1 per 2 students
Quantity
2
9
2
3
6
6
1
1
6
1
1
1
1

Practical problems (official English version), 49th IChO 2017, Thailand

5AAA-1Student CodeTask 1A
13%
Total
Score

a
a1
12

a2
2

b1
6

b
b2
1

c
b3
1

c1
2

Total
c2
2

26

Accounted For 13% of Total Score
Task 1A: Acid-base indicator and its application for pH measurement
Acid-base indicators are weak acids (or bases) that exhibit different colors when they
are present in solution as their acidic form (HIn, color 1) or as their basic form (In-, color 2).
They undergo the following reaction in dilute aqueous solution.
HIn

H+ + In-As the pH of a solution containing the indicator changes, the equilibrium shown above will be
driven either towards reactants (HIn), or products (In-) causing the solution color to change
depending on the concentration of each form present. In strongly acidic solution, most of theindicator will be present in the HIn form (color 1) and in strongly basic solutions, most of theindicator will be in the In- form (color 2). At intermediate pH values, the solution color will
be a mix of color 1 (absorption at wavelength 1) and color 2 (absorption at wavelength 2),
depending on the relative amounts of HIn and In- present.
By monitoring the absorbance values at two wavelengths, the concentrations of HIn and In can be calculated by using the following expressions.
Aλ1total= Aλ1HIn + Aλ1In=  λ1HIn b[HIn] +  λ1In-b[In-]Aλ2total= Aλ2 HIn + Aλ2In=  λ2HIn b[HIn] +  λ2In-b[In-]where b is pathlength of solution and  is the molar absorptivity.
At a certain pH value, the relative amounts of HIn and In- in solution are related to the aciddissociation constant (Ka) of the indicator, as shown in the following equation.
Ka = [H+][In-][HIn]

Therefore, for a given pH value, acid dissociation constant (Ka) of the indicator can becalculated when the relative amounts of HIn and In- in solution are known.

Practical problems (official English version), 49th IChO 2017, Thailand

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Student Code

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Experimental Set-up
Instructions for using a spectrophotometer
1. Set a spectrophometer to measure the absorbance at the desired wavelength following theprocedure shown in the diagram.
2. Wipe the outside of a cuvette containing distilled water and insert the cuvette into the sample
compartment.
3. Adjust the zero absorbance using water.
4. Remove the cuvette, replace water in the cuvette by sample solution to be analyzed. Make
sure to tap out any bubbles and wipe the outside of the cuvette before placing the cuvetteinto the sample compartment.
5. Read the absorbance value of the sample.
Note: When changing the wavelength, make sure to adjust zero absorbance using “water”.

Spectrophotometer No.
Sample Compartment

ScreenKeypadPractical problems (official English version), 49th IChO 2017, Thailand

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Student Code

AAA-1

Step 1: Press 1

1 Press [1]1 Press
Press 1[1]icon on the keypad to select Photometric mode2
2

Press [1] icon on the touchscreen to selectPressNote:[1] iconthemenu
touchscreen
selectPhotometric
mode
If
theon
main
as shown intothe
left picture is not displayed on the
Photometricmode
screen, press [return] on the keypad.

P
siNote : If the main menu as shown in the left picture is not displayed[1]
1 Presson Notethe screen,[return]ason
the keypad.
: If the press
main menu
shownin the left picture is not displayed2on the screen, press [return] on the keypad.
Press [1] icon on the touchscreen to selectPhotometric mode

Press [1] on the touchscreen to
single wavelength mode

Note : If the main menu as shown in the left picture is not displayedon the screen, press [return] on the keypad.

2

elect

Press [1]Press
Step 2: [1]Press 1PressPress[1] onthe touchscreen
to select
Photometric
1 iconon the keypad
to select
Photometric mode single
single wavelength modemode
the wavelength
3 Setwavelength
3 Set the wavelengthe is not displayed[GOTO WL] on the keypad to set thethe wavelength
3 SetPress

4

Press [GOTO WL] on the keypad to set the
wavelength

Press [GOTO
WL] 3:
on Setthe keypad
to set theStep
the wavelength
wavelength
wavelength

Get the Abso

Rinse with water 1 - 2 me
Rinse with water 1 - 2 me
Rinse with water 1 - 2 meFill the solu on around ¾
Place
cuvetteconta
of cuve Fille height& Wipewithpaper
the solu
on around¾
Fill the solu on around ¾
compartme& Wipe with
paperof cuve e height & Wipe with paper of cuve e height sample

Press [GO TO WL] on the keypad to set the wavelength

Press number on the keypad
Press number
the keypadPressnumberon the keypad[1]
2 onPress

en to selectsettheis not displayed
ftselectpictured.

re is not displayed[AUTO ZERO] on t
Note : Press
For example,
if the ondesirednumberthewavelength
keypad is 432 nm,
Place cuvette conta
Note
if the desired wavelength is 432 nm,
4 3: keypad.
2For
onexample,
the keypad.
press 4press
3 2 on thesolution in the sam
Press
[1]
on
the
touchscreen to select Photometric
press
4
3
2
on
the
keypad.
Note: For example, if the desired wavelength is 432, press 4 3 2 on the keypad. measure the absor
single wavelength mode

Note : For example, if the desired wavelength is 432 nm,

2Press [1]Get the Absorbance value

4

Press
[ENTER]on thekeypadPress[1]Presson thePress
touchscreen
to select
Photometric[ENTER]on keypadthekeypad[ENTER]onthesingle wavelength
Press mode
[ENTER]onthe
Place cuvettekeypadcontaining water in the

Rinse with water 1 - 2 me

[GO TO WL]  4 3 2  [ENTER]

Fill the solu on around ¾ Note : If the Abs is not displayed on the screen, press [F1] on thesample compartment and pressof cuve e height & Wipe with paper
Repeat Step 3-4 to measure the absorbance at
keypad to switch between %T & Abs.

Note : If the Abs[AUTO
is not displayedon thepress [F1] on theZERO]
on screen,thekeypadanother
wavelength
NoteNote:: Ifswitch
theisnotisdisplayed
screen,
press
[F1]
on
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Repeat
3-4 to measure
keypadtobetween%T
Abs.on the on
If AbstheAbs
not&displayed
the screen,press[F1] on the
keypad Steptos 432 nm,keypadto switch
between%T &Abs
Abs.
Place
cuvettecontaining sample
switchbetween%T andsolution in the sample compartment tomeasure the absorbance4

pad to set theto set thepress [F1] on theelengthis 432 nm,
is 432 nm,

Rinse with DI
water
Rinse
with water 1 - 2 me

4

Repeatwavelength
Step 3-4 to measureanotheranother wavelength

Get the Absorbance value

Get the Absorbance value

Step 4: Get the absorbance value

Place cuvette containing water in thePlacecuvette containing
water in theFill thesolu toon around
RepeatStep
3-4
measuretheabsorbanceat compartment
FillFillthe
solutionaround¾ of ¾
sampleand press
the solu
around¾
of oncuve
e height& Wipe with paperPlacecuvettesamplecompartment
andpress containing water in the sample
of cuve e height & Wipe with paper
another
wavelength
[AUTO
ZERO]
on
the
keypadthe cuvetteheight and wipe
[AUTO ZERO] oncompartment
the keypadand press [AUTO ZERO] on the keypad.
with paper
Place cuvettecontaining sample
Place cuvette containing
samplesolution in the sample
to compartment
solutionin the sample
Placecompartment
cuvettecontaining
sampletosolution in themeasure the absorbancemeasuretheabsorbancesample compartment to measure the absorbanceRinse with water 1 - 2 medn, press [F1] on themeasurethe absorbanceatscreen, press [F1] on theRepeat Step 3-4 to
RepeatStep
3-4 to measure
the absorbance at another wavelength

Step 3-4 to measure the absorbance atanother Repeat
wavelength
another wavelength

Practical problems (official English version), 49th IChO 2017, Thailand

8

Student Code

AAA-1

General Information
In 0.1 mol dm-3 HCl, indicators are in the acidic form (HIn) only.
In 0.1 mol dm-3 NaOH, indicators are in the basic form (In-) only.

There will be no mark for the answer in the dotted line box.
NOTE:

Students are suggested to check the spectrophotometer before use by measuring theabsorbance values of the instrument check solution at two different wavelengths, i.e., 430 and
620 nm.
Spectrophotometer No. ________ is used throughout the experiment.

Record the absorbance values of the instrument check solution
A (at 430 nm)
Measured value
Guided value

A (at 620 nm)________________ ________________
0.220 – 0.260

0.450 – 0.510

In case that the measured values are within the guided values, students can proceed withfurther experiments. If not, students can ask for assistance.

Part aAbsorbance measurement of an acid-base indicator (methyl orange) in strong acid andstrong base
1. Pipette 1.50 cm3 of 2.00  10-4 mol dm-3 methyl orange indicator solution into a 25.00cm3 volumetric flask, add 2.5 cm3 of 1 mol dm-3 HCl into the flask and make up to thevolume using distilled water. Record the absorbance at 470 and 520 nm.
2. Pipette 2.00 cm3 of 2.00  10-4 mol dm-3 methyl orange indicator solution into a 25.00cm3 volumetric flask, add 2.5 cm3 of 1 mol dm-3 NaOH into the flask and make up to thevolume using distilled water. Record the absorbance at 470 and 520 nm.
3. Calculate the molar absorptivities at 470 and 520 nm of acidic and basic forms of methyl
orange.

Practical problems (official English version), 49th IChO 2017, Thailand

9Student CodeAAA-1a1) Record the absorbance values of methyl orange in acid and basic solutions(You do not need to fill the entire table.)methyl orange in acidic form
Replicate 1
Replicate 2
Replicate 3
Accepted value(3 digits after decimal point)

methyl orange in basic form
Replicate 1
Replicate 2
Replicate 3
Accepted value(3 digits after decimal point)

A (at 470 nm)

A (at 520 nm)__________________________A (at 470 nm)

A (at 520 nm)__________________________

a2) Calculate the molar absorptivities of the acidic form and basic form of methyl orange(unit, dm3 mol-1 cm-1)
Blank area for calculation

Practical problems (official English version), 49th IChO 2017, Thailand

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Student CodeAAA-1

The molar absorptivities of methyl orange are as follows: (unit, dm3 mol-1 cm-1)
acidic form (HIn)
470
 HIn
520HIn

methyl orange____________

basic form (In-)
470In520In-____________ ____________ ____________Part b
Absorbance measurement of an acid-base indicator (bromothymol blue) in buffer
solution
Bromothymol blue is an acid-base indicator which shows yellow color when it is present as anacidic form (HIn) and it shows blue color when it is present as a basic form (In-). The
absorption maximum of the bromothymol blue in the acidic form is at 430 nm and that in thebasic form is at 620 nm. The molar absorptivities of bromothymol blue in the acidic form are
16,600 dm3 mol-1 cm-1 at 430 nm and 0 dm3 mol-1 cm-1 at 620 nm. The molar absorptivities ofbromothymol blue in the basic form are 3,460 dm3 mol-1 cm-1 at 430 nm and 38,000 dm3 mol-1
cm-1 at 620 nm.

1. Pipette 1.00 cm3 of 1.00 × 10-3 mol dm-3 bromothymol blue indicator solution into a
25.00-cm3 volumetric flask, and make up to the volume using solution A. (Note: solution
A is a buffer solution pH = 7.00)
2. Record the absorbance at 430 and 620 nm.
3. Calculate the concentrations of the acidic form and basic form of bromothymol blue
indicator solution in the volumetric flask.
4. Calculate the acid dissociation constant of bromothymol blue.

b1) Record the absorbance values of bromothymol blue in buffer solution(You do not need to fill the entire table.)
bromothymol blue in buffer solution
Replicate 1
Replicate 2
Replicate 3
Accepted value(3 digits after decimal point)

A (at 430 nm)

A (at 620 nm)_____________ _____________

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Student CodeAAA-1b2) Calculate the concentrations of the acidic form and basic form of bromothymol blue
indicator in the resulting solution
Blank area for calculation

The concentrations of the acidic form and basic form of bromothymol blue in the resulting
solution are as follows:[HIn], mol dm-3

[In-], mol dm-3______________________________________(3 significant figures)(3 significant figures)b3) Calculate the acid dissociation constant of bromothymol blue from this experiment.
Blank area for calculation

The acid dissociation constant of bromothymol blue from this experiment is as follows:

The acid dissociation constant = ___________________________(3 significant

figures)

Practical problems (official English version), 49th IChO 2017, Thailand

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Student Code

AAA-1

Part cDetermination of solution pH by using acid-base indicator (methyl red)
Methyl red is an acid-base indicator which shows reddish-pink color when it is present as anacidic form (HIn) and it shows yellow color when it is present as a basic form (In-). The molar
absorptivities of methyl red in the acidic form are 9,810 dm3 mol-1 cm-1 at 470 nm and 21,500
dm3 mol-1 cm-1 at 520 nm. The molar absorptivities of methyl red in the basic form are 12,500
dm3 mol-1 cm-1 at 470 nm and 1,330 dm3 mol-1 cm-1 at 520 nm. The pKa of methyl red is 4.95.
Note: There is no need to accurately measure the volumes used in this part, as it does not affectthe accuracy of the results obtained.

1. Fill a test tube to one quarter with solution of unknown pH X. Add three drops of methyl
red into the solution and mix thoroughly. Record the color.
2. Fill a test tube to one quarter with solution of unknown pH Y. Add three drops of methyl
red into the solution and mix thoroughly. Record the color.
3. Fill a test tube to one quarter with solution of unknown pH Z. Add three drops of methyl
red into the solution and mix thoroughly. Record the color.
Record the color change of indicator in sample solutions (no mark)indicator
in sample X

Color observedin sample Yin sample Z

Methyl redc1) Select one solution from the three sample solutions, of which the pH can be determined
spectrophotometrically by using methyl red as an indicator.

 Sample X

 Sample Y Sample Z

4. Use a measuring cylinder to transfer 10 cm3 of the selected unknown solution into abeaker. Add three drops of methyl red indicator into the solution and mix thoroughly.
Record the absorbance at 470 and 520 nm.
5. Calculate the concentration ratio of basic form and acidic form of methyl red in thesolution.
6. Calculate the pH of the selected unknown solution.

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Student Code

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Record the absorbance values of the resulting solution
selected unknown solution

A (at 470 nm)

A (at 520 nm)c2) Calculate the concentration ratio of the basic form and acidic form of methyl red indicatorin an unknown solution and the pH value of the unknown solution
Blank area for calculation

The concentration ratio of the basic form and acidic form of methyl red indicator in an unknown
solution and the pH value of the unknown solution are as follows:
sample[In-] / [HIn]_________________(2 digits after decimal point)pH_____________(2 digits after decimal point)

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Student Code

AAA-1

Practical Exam
Task 1B

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Student CodeAAA-1

Chemicals and Equipment (Task 1B)
I. Chemicals and materials (the actual labeling for each is given in bold font)Health Statementsa
Solution A (KIO3 10.7042 g in 5.00 dm3), 60 cm3
H272-H315-H319-H335
in a plastic bottle
Solution B (Saturated Ca(IO3)2 solution), 50 cm3 in
H272-H315-H319-H335
a plastic bottle
Solution C (Saturated Ca(IO3)2 in unknown dilute
H272-H315-H319-H335
3
KIO3 solution), 50 cm in a plastic bottle
Solution of Na2S2O3 200 cm3 in a plastic bottle
KI 10% (w/v), 100 cm3 in a plastic bottle
H300+H330-H312-H315-H319H335
HCl 1 mol dm-3, 100 cm3 in a plastic bottle
H290-H314-H335
3
Starch solution 0.1% (w/v), 30 cm in a dropping
glass bottle
Distilled water, 500 cm3 in a wash bottle
Distilled water, 1000 cm3 in a plastic gallon
aSee page xx for definition of Risk and Safety Phrases
II. Equipment and labwares
Personal Labwares
Beaker, 100 cm3
Beaker, 250 cm3
Erlenmeyer flask, 125 cm3Transfer pipette, 5.00 cm3Transfer pipette, 10.00 cm3
Measuring cylinder, 10.0 cm3
Measuring cylinder, 25.0 cm3
Pasteur pipette
Rubber bulb for Pasteur pipette
Glass funnel, 7.5 cm diameter
Plastic funnel, 5.5 cm diameter
Filter paper in a zipped bag
Burette, 50.0 cm3
Burette stand and clamp
O-ring with bosshead

Quantity
2
1
9
2
1
1
2
1
1
2
1
3
1
1
2

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AAA-1Student CodeTask 1B
Total
Score

a1
1

a
a2
5

a3
1

b1
6

b
b2
1

b3
2

c1
6

c
c2
1

Total
c3
3

26

Accounted for 13% of Total Score
Task 1B: Calcium iodate
Calcium iodate is an inorganic salt composed of calcium and iodate ions. Ca(IO3)2 issparingly soluble in water. Equilibrium is established between the undissolved salt andsaturated solution of the salt.
Ca(IO3)2 (s)Ca2+(aq) + 2 IO3- (aq)

Titration data will be used to determine the concentration of iodate ions in a saturated
solution of Ca(IO3)2 and then to determine the value of Ksp for Ca(IO3)2.
The concentration of iodate ion will be determined by titration with a standard solutionof sodium thiosulfate (Na2S2O3), in the presence of potassium iodide (KI). Starch will be used
as an indicator.
Part a is associated with the standardization of Na2S2O3. Part b is the determination ofKsp for Ca(IO3)2.
In Part C, solid Ca(IO3)2 is dissolved in an unknown dilute KIO3 solution. After
standing for 3 days, equilibrium is also established between the undissolved salt and saturated
solution of the salt. The concentration of iodate ion will be determined using the same
titrimetric method, and then used to calculate the concentration of the dilute KIO3 solution.

Part aStandardization of Na2S2O3

1. Fill the burette with Na2S2O3 solution.
2. Pipette 10.00 cm3 of standard KIO3 solution (provided as solution A, KIO3 10.7042 g
in 5.00 dm3) into an Erlenmeyer flask. Add 10 cm3 of 10%(w/v) KI and 10 cm3 of 1
mol dm-3 HCl into a flask. The solution should turn dark brown as I2 is formed.
3. Titrate with Na2S2O3 solution until the solution has turned pale yellow. Add 2 cm3 of
0.1%(w/v) starch solution. The solution should turn dark blue. Titrate carefully to thecolorless endpoint. Record the volume of Na2S2O3 solution.

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Student CodeAAA-1a1) Balance relevant chemical equations.

…… IO3 (aq) +…… I-(aq) + …... H3O+ (aq)  …… I2(aq) + …… H2O(l)……I2 (aq) + …… S2O32-(aq)  …… I-(aq) + …… S4O62-(aq)a2) Record volume of Na2S2O3 solution.
(You do not need to fill in the entire table)
Titration no.
1

2

3

Initial reading of the burette of Na2S2O3 solution, cm3
Final reading of the burette of Na2S2O3 solution, cm3
Consumed volume of Na2S2O3 solution, cm3
Accepted volume, cm3;V1 =a3) Calculate the concentration of the Na2S2O3 solution.

Concentration of Na2S2O3 , mol dm-3: …………… (answer in 4 digits after decimal point)(If the student cannot find the concentration of Na2S2O3, use the concentration of 0.0700 mol
dm-3 for further calculations.)

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Student Code

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Part bDetermination of Ksp of Ca(IO3)2

1. You are provided with the filtrate of the filtered saturated solution of Ca(IO3)2.
(Solution B)
2. Pipette 5.00 cm3 of the filtrate into an Erlenmeyer flask. Add 10 cm3 of 10% (w/v) KI
and 10 cm3 of 1 mol dm-3 HCl into a flask.
3. Titrate with Na2S2O3 solution until the solution has turned pale yellow. Add 2 cm3
0.1% (w/v) starch solution. The solution should turn dark blue. Titrate carefully to thecolorless endpoint. Record the volume of Na2S2O3 solution.

b1) Record volume of Na2S2O3 solution.
(You do not need to fill in the entire table)
Titration no.
1

2

3

Initial reading of the burette of Na2S2O3 solution, cm3
Final reading of the burette of Na2S2O3 solution, cm3
Consumed volume of Na2S2O3 solution, cm3
Accepted volume, cm3;V2 =b2) Calculate the concentration of the IO3- solution.

Concentration of IO3- , mol dm-3: …………………(answer in 4 digits after decimal point)

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Student CodeAAA-1b3) Calculate value of Ksp for Ca(IO3)2.

Ksp for Ca(IO3)2 = ……………………………………(answer in 3 significant figures)(If the student cannot find Ksp, use the value of 710-7 for further calculations.)

Part cDetermination of concentration of unknown dilute KIO3 solution

1. You are provided with the filtrate of the filtered saturated solution of Ca(IO3)2 dissolvedin the unknown dilute KIO3 (provided as solution C).
2. Pipette 5.00 cm3 of the filtrate solution into an erlenmeyer flask. Add 10 cm3 of 10%(w/v) KI and 10 cm3 of 1 mol dm-3 HCl into a flask.
3. Titrate with Na2S2O3 solution until the solution has turned pale yellow. Add 2 cm3
0.1% (w/v) starch solution. The solution should turn dark blue. Titrate carefully to thecolorless endpoint. Record the volume of Na2S2O3 solution.

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Student CodeAAA-1c1) Record volume of Na2S2O3 solution(You do not need to fill in the entire table)
Titration no.
1

2

3

Initial reading of the burette of Na2S2O3 solution, cm3
Final reading of the burette of Na2S2O3 solution, cm3
Consumed volume of Na2S2O3 solution, cm3
Accepted volume, cm3; V3 =c2) Calculate the concentration of the IO3- in solution C.

Concentration of IO3-, mol dm-3: ……………………(answer in 4 digits after decimal point)

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Student CodeAAA-1c3) Calculate the concentration of the unknown dilute KIO3 sample.

Concentration of IO3- , mol dm-3: ………………

(answer in 4 digits after decimal point)

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Student Code

AAA-1

Practical Exam
Task 2

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Student CodeAAA-1

Chemicals and Equipment (Task 2).
I. Chemicals and materials
Chemicals
3-Pentanone (MW 86.13),~0.86 gb in a vial
p-chlorobenzaldehyde (MW140.57),~3.5 gc in a vial

Labeled as

Health Statements aA

H225-H319-H335-H336

B

H302-H315-H319-H335

Ethanol, 200 cm3 in a wash-bottle

Ethanol

H225-H319

2N NaOH

H290-H314-3

2 mol dm NaOH solution in water(labelled as 2N NaOH), 25 cm3 in a bottlea

See page 34 for definition of Health Statements
You will need to weigh the vial containing 3-pentanone right before using. The exact value
can be calculated based on the information given on the label.
c
The exact value is indicated on the label.
b

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II. Equipment and labwares
Shared equipment
Balance

Quantity
Shared 12 per room

Water aspirator

Shared 2 per bench

Foam bucket filled with ice

Shared 1 per row (Refill could berequested)
Quantity
1

Personal Equipment
Hotplate stirrer with temperature probe
Stand

1

Clamps2100-cm3 Round bottom flask

1

Measuring cylinder, 25 cm3

1

3

1

Measuring cylinder, 50 cm
Air condenser

1

Crystallizing dish, 250 cm

3

3

1

125-cm Erlenmeyer flask

2

Suction flask, 250 cm3

1

Buchner funnel, 25 cm

3

1

Watch glass

1

Pasteur pipettes (droppers)

5

Rubber bulbs

2

Suction rubber

1

Rubber support ring

1

Magnetic bar

1

Filter papers

3 (pack in 1 zipped bag)Spatula1

Stirring Rod

1

Forceps1

Plastic joint clips

1

Wash Bottle (filled with EtOH)
Nitrile gloves

1 (can be refilled)
2 (exchange size if needed)

Towels2Paper clip

1

“Waste Task 2”, 500 cm -glass bottle

1

Vial labeled “Student code” for submitting
product.
Goggles131

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Student CodeTask 2
Total
Score

a1
2

a
a2
2

a3
2

AAA-1
b
b1
18

Total
24

Accounted for 14% of Total Score

Task 2: Elaborating Carbon Framework
The core structure of organic molecules is mostly based on carbon-carbon skeleton.
Carbon-carbon bond formations have played a vital role in the construction of complex
structures from smaller starting materials. Therefore, the synthetic transformations toefficiently achieve carbon-carbon bond formation has long been of interest. In this experiment,
you are required to transform commercially available p-chlorobenzaldehyde and 3-pentanone
to a more elaborated structure.

Important Notes:


Ethanol can be refilled with no penalty.

All weighing processes require verification from lab supervisor. The supervisor willneed to sign in the student’s answer sheet for grading. No mark will be given forunverified values.



Total of 18 points of this exam score will be based on the quality and quantity of the
product submitted. We could not give any score on this part if the product is not
submitted for grading.

1

H-NMR and melting point determination techniques will be used by the grader toverify the quality of your product.

Part a
1. Take the vial containing 3-pentanone (A) (Code Axxx, For example: A305) and unwrap
the parafilm. Weigh the vial with caps. Record the weight in the answer sheet question
a1.
2. Setup a water bath by filling water in the 250 cm3-crystallizing dish and heat to 55±2°C.
Add paper clip into the water bath and let it stir so that the heat could be distributed
evenly.
3. Ensure a magnetic stirring bar is in the 100-cm3 round bottom flask. Transfer the preweighed 3-pentanone (labeled as A) and p-chlorobenzaldehyde (labeled as B) to theflask. Add 50 cm3 ethanol to the mixture and swirl to dissolve.
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Student CodeAAA-1

4. Measure 15 cm3 of 2 mol dm-3 NaOH (labeled as 2N NaOH) using a measuring cylinderand add to the reaction mixture. Be careful not to wet the ground joint with NaOH
solution.
5. Setup the reaction as shown in Figure 1. The reaction flask is placed in the 55±2°C

water bath. Attach the air condenser to the reaction flask with plastic joint clip. Heat
the reaction mixture while stirring for 30 minutes using the water bath.

Figure 1: Set up needed for heating the reaction with water bath.

6. Remove the reaction flask from the water bath. (Be careful! The flask might be hot.)Place the flask on the rubber supporting ring.
7. (Important) Detach the probe from the hotplate/stirrer to avoid over-heating of the hotplate in
the recrystallizing steps. After you detach the probe, inform the supervisor to check and submit
the probe to the supervisor.
8. Prepare the ice bath by replacing the warm water in the 250 cm3-crystalizing dish with

ice and small amount of water. Place the reaction flask on the ice bath to cool down thereaction. Solid should be observed. (Suggestion: If you do not observe any solid within
5 minutes, you may use a stirring rod to scratch the side of the flask. This could induce
precipitation.)
9. Keep the mixture cool for approximately 20 minutes to allow complete precipitation.

10. Set up the suction filtration equipment (Figure 2). Connect the suction flask to the water

aspirator. Place a Buchner funnel fitted with a rubber adapter onto the suction flask.
Place a filter paper at the center of the funnel. Filter the precipitate via suction filtration
and wash the precipitate with small amount of cold ethanol. Let air suck through theprecipitates for 2-3 minutes to dry the product.
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Student Code

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Figure 2: Set up needed for suction filtration.

11. Disconnect the vacuum (before turning off the water aspirator). Bring your equipment
back to your space and keep the common area clean. Collect the crude precipitates fromthe filter paper and transfer to the Erlenmeyer flask. Careful not to scrape the paper
too hard as you may obtain small pieces of paper as contaminant. Student may use
Ethanol to rinse the Buchner funnel.
12. Place ethanol in a separate Erlenmeyer flask and heat it gently on a hotplate. (Student
may set the temperature mark at 100-120°C) Before heating, please make sure thatthe temperature probe is detached from the hotplate.
13. Recrystallize the product from hot ethanol. You can follow the procedure below.
Add small amount of hot ethanol to the flask containing crude solid while swirling.
Continue addition of hot ethanol (swirling after each addition) until the solid iscompletely dissolved. During the dissolution process, keep the flask hot at all times byresting it on the hotplate. Be careful that the flask may be hot. You may use paper
towels or towels provided to wrap around the flask while swirling. Once the dissolution
is complete, set the flask containing the dissolved compound on a benchtop and let theflask cool down to room temperature without disturbance. The crystalline productshould be observed. If not, you may use the stirring rod to scratch the side of the flask
to induce crystallization. Place the flask into the ice bath to complete crystallization.
14. Filter the recrystallized product via suction filtration (See step 10 for suction filtration
protocol) and wash the product with small amount of cold ethanol. Let air suck throughthe precipitates for 2-3 minutes. Disconnect the vacuum. Let the purified product airdry on the benchtop for at least 15 minutes.

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15. Weigh the vial (without cap) labeled with your student code provided. Record the value
in the answer sheet question a1.
16. Transfer the recrystallized product to the pre-weighed vial. Determine and record themass of the purified product in the answer sheet question a1.
17. Fill the information on the label of the product vial. Place the product-containing vialon the benchtop. The supervisor will pick up your vial and sign on your answer sheetquestion b after the “Stop command”. The student also must sign the answer sheetquestion b for grading. Once both supervisor and student sign, place the vial into azipped bag and submitted for grading.

These following items should be left on your bench: The exam/answer booklet (this booklet) placed in an exam envelope The vial labeled “Student Code” with filled information

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Supervisor will place a label here
when randomly distributed the compounds:

Axxx (For example: A567) =Tared (w/caps):
Bxxx (For example: B567) =Net:

Code of vial containing 3-pentanone
Mass of (vial + label + caps) before adding 3-pentanone
Code of vial containing p-chlorobenzaldehyde
Mass of p-chlorobenzaldehydea1) Use the information provided in the label above along with your experimental data foryour calculation. Write down all the results in this Table.

Mass of 3-pentanone in the vial provided (must weigh with caps) = ________________*Signature of the supervisor is required for grading

Mass of pentan-3-one = _____________________________
Mass of p-chlorobenzaldehyde (copy from the label):_________________________

Mass of the empty vial for product:____________________________*Signature of the supervisor is required for grading

Mass of the vial with the recrystallized product:_____________________________*Signature of the supervisor is required for grading

Mass of the recrystallized product:_____________________

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Student CodeAAA-1a2) Write 4 plausible aromatic compounds that may occur from this reaction. Stereoisomers
are excluded.

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Student CodeAAA-1a3) Given the 400MHz 1H-NMR (in CDCl3) of the product below, write the structure of the
product.

Frequency

H2O

CHCl3

Integral

8

TMS

2
2

2
2

6
2

Integrals are for all protons presented in the molecule.

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Student Code

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Part bb1) Your submitted product will be characterized and graded for its %yield and purity.
Provide information of the product you submitted.

Status:Solid

LiquidSignature of Supervisor: ___________________________(Signed when submitted)

Signature of Student: _____________________________ (Signed when submitted)

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Student Code

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Health Statements

H225

Highly flammable liquid and vapor

H272

May intensify fire; oxidizer

H290

Maybe corrosive to metals

H300

Fatal if swallowed

H301

Toxic if swallowed

H302

Harmful if swallowed

H314

Causes severe skin burns and eye damage

H315

Causes skin irritation

H319

Causes serious eye irritation

H330

Fatal if inhaled

H335

May cause respiratory irritation

H336

May cause drowsiness or dizziness

H371

May cause damage to organs

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Student Code

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Characteristic 1H NMR Chemical Shifts
Type of Hydrogen(R=Alkyl, Ar=Aryl)

Chemical Shift(ppm)

Type of Hydrogen(R=Alkyl, Ar=Aryl)(CH3)4Si

0 (by definition)

RCH3

0.9

RCH=O

9.5-10.1

RCH2R

1.2-1.4

RCOOH'

10-13

R3CH

1.4-1.7

RCOCH3

2.1-2.3

RCH2I

3.2-3.3

RCOCH2R

2.2-2.6

RCH2Br

3.4-3.5

RCOOCH3

3.7-3.9

RCH2Cl3.6-3.8

RCOOCH2R

4.1-4.7

RCH2F

4.4-4.5

R2C=CRCHR2

1.6-2.6

RCH2NH2

2.3-2.9

R2C=CH2

4.6-5.0

RCH2OH

3.4-4.0

R2C=CHR

5.0-5.7

RCH2OR

3.3-4.0RC≡CH

2.0-3.0

RCH2CH2OR

1.5-1.6

ArCH3

2.2-2.5

R2NH

0.5-5.0

ArCH2R

2.3-2.8

ROH

0.5-6.0ArH

6.5-8.5

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Chemical Shift
(ppm)

35

Student Code

AAA-1

Periodic table of elements

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