Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
S.K.H. Kei Hau Secondary School
Chemistry TAS Project
Experiment 22-25
Project on analysis of
Vitamin C in fruit
5/17/01, 5/24/01, 5/31/01, 6/7/01, 6/14/01
Report by K.F.Leung
INDEX PAGE
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Table of Contents
Table of Contents ...................................................................................................... 1
Aim................................................................................................................................ 3
Introduction ............................................................................................................... 3
Materials used ........................................................................................................... 9
Procedures ................................................................................................................ 10
1.
2.
3.
4.
5.
6.
Measuring the mass of potassium iodate(V) used by ‘weigh by
difference’ method ................................................................................. 10
Preparation of potassium iodate(V) solution ...................................... 10
Standardization of the sodium thiosulphate solution ........................ 10
Preparation of fruit juice ...................................................................... 10
Titration between the fruit juice mixture and the sodium
thiosulphate solution ............................................................................. 11
Investigation of the other fruits ........................................................... 11
Results........................................................................................................................ 12
1.
2.
3.
4.
Investigation of Mr. JuiceTM Orange Juice ....................................... 12
Investigation of McDonald’sTM Ketchup .......................................... 13
Investigation of Fresh Lemon .............................................................. 14
Investigation of the Same Lemon which was kept in
5.
refrigerator(~4oC) One Week After .................................................... 15
Investigation of *YourLife® Vitamin C Tablet .................................. 16
Data Analysis ........................................................................................................... 18
1.
2.
3.
4.
5.
Investigation of Mr. JuiceTM Orange Juice ....................................... 18
Investigation of Mcdonald’sTM Ketchup: ......................................... 21
Investigation of Fresh Lemon .............................................................. 23
Investigation of Same Lemon One Week After keeping in 4oC ........ 26
Investigation of YourLife® Vitamin C Tablet .................................... 28
Conclusion................................................................................................................ 31
Discussion................................................................................................................. 32
Precautions............................................................................................................... 35
Related web-links ................................................................................................... 36
News Scripts About Vitamin C............................................................................ 37
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Aim
Find out the vitamin C content in different kinds of fruit
Types of fruit:
Any kinds of juicy fruit such as orange, lemon and kiwi fruit which may get a better
result.
Introduction
itamin C functions physiologically as a water-soluble
antioxidant by virtue of its high reducing power. It is a
cofactor for enzymes involved in the biosynthesis of collagen,
carnitine, and neurotransmitters in vitro, and it can quench a
variety of reactive oxygen species and reactive nitrogen species
V
in aqueous environments. Evidence for in vivo antioxidant
functions of ascorbate include the scavenging of reactive
oxidants in activated leukocytes, lungs, and gastric mucosa, and diminished lipid
preoxidation as measured by urinary isoprostane excretion.
To provide antioxidant protection, a Recommended Dietary Allowance (RDA)
of 90 mg per day for adult men and 75 mg per day for adult women is set based on
the vitamin C intake to maintain near-maximal neutrophil concentration with
minimal urinary excretion of ascorbate. Because smoking increases oxidative stress
and metabolic turnover of vitamin C, the requirement for smokers is increased by 35
mg per day. Estimates of median dietary intakes of vitamin C for adults are 102 mg
per day and 72 mg per day in the US and Canada, respectively. The Tolerable Upper
Intake Level (UL) for adults is set at 2 g per day; the adverse effects upon which are
the UL is based are osmotic diarrhea and gastrointestinal disturbances.
Vitamin C is a water-soluble vitamin that is essential for all humans and a few
other mammals that lack the ability to biosynthesize the compound from glucose
because they lack the enzyme gulonolactone oxidase. The term vitamin C refers to
both ascorbic acid and dehydroascorbic acid (DHA), since both exhibit
anti-scorbutic activity. Ascorbic acid, the functional and primary in vivo form of the
vitamin, is the enolic form of an α-ketolactone
(2,3-didehydro-1-threo-hexano-1,4-lactone). The two enolic hydrogen atoms give
the copound its acidic character and provide electons for its function as a reductant
and antioxidant. Its one-electon oxidation product, the ascorbyl radical, readily
dismutates to ascorbate and DHA, DHA are readily reduced back to ascorbic acid in
vivo. However, DHA can be hydrolyzed irreversibly to 2,3-diketogulonic acid. The
molecular structure of ascorbic acid contains an asymmetric carbon atom that allows
two enantiomeric forms.
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Functions
The biological functions of ascorbic acid are based on its ability to provide
reducing equivalents for a variety of biochemical reaction. Because of its reducing
power, the vitamin can reduce most physiologically relevant reactive oxygen species
(Buettner, 1993). As such, the vitamin functions primarily as a cofactor for reactions
requiring a reduced iron or copper metalloenzyme and as a protective antioxidant
that operates in the aqueous phas both intra- and extracellularly (Englard and Seifter,
1986; Halliwell and Whiteman, 1997; Tsao, 1997). Both the one- and the
two-electron oxidation products of the vitamin are readily regenerated in vivo –
chemically and enzymatically – by glutathione, nicotinamide adenine dinucleotide
(NADH) and nicotinamide adenine dinucleotide phosphate (NADPH), and
nicotinamide adenine dinucleotide phosphate (NADPH) dependent reductases (May
et al., 1998; Park and Levine, 1996).
Vitamin C is known to be an electron donor for eight human enzymes, Three
participate in collagen hydroxylation; two in carnitine biosynthesis; and three in
hormone and amino acid biosynthesis. The three enzymes that participate in
hormone and amino acid biosynthesis are dopamine-β-hydroxylase, necessary for
the biosynthesis of the catecholamines norepinephrine and epinephrine;
peptidyl-glycine monooxygenase, necessary for amidation of peptide hormones; and
4-hydroxyphenylpyruvatedioxygenase, involved in tyrosine in tyrosine metabolism.
Ascorbate’s action with these enzymes involves either monooxygnase or
dioxygenase activities (Levine et al. 1996b).
As a cofactor for hydroxylase and oxgenase metalloenzymes, ascorbic acid is
believed to work by reducing the active metal site, resulting in reactivation of the
metal-enzyme complex, or by acting as a co-substrate involved in the reduction of
molecular oxygen.
From our basic level, deficiency of vitamin C will cause scurvy, a symptoms of
which include breakdown of connective tissues and blood vessels. Scurvy was once
common among sailors who were depreived of fresh fruit and vegetables containing
vitamin C while on long voyages. In the 16th centuries, many sailors suffered from
scurvy. Bleeding of the gums, loosening of the teeth and some internal bleeding also
occurs in many sailors. However, a doctor prescribed them eating fresh fruit and
vegetable, they recovered miraculously. After that, Dr. James Lind found that there
is a substance inside green vegetable to cure the scurvy. But that time it was not
known that a few milligrams of vitamin C in the food was the active agent in the
recovery.
In everyday case, the existence of the vitamin was known before it was isolated
from its food sources and identified chemically. Hence vitamins were given letters at
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
first, but now that their chemical nature is known the chemical names, e.g. ascorbic
acid for vitamin C, are common to use.
Vitamin C is thought to act as an electron carrier in respiration. It also
stimulates synthesis of collagen fibres. Thus deficiency of vitamin C causes scurvy.
Elderly people always have bruised patches appear in their skin as they may
inadequate consuption of fresh fruit and vegetables.
In many recent research, a high daily intake of vitamin C in the diet may have
many beneficial effects, including reduction of blood cholesterol.
Functions in conclusion:
Production of collagen fibres
Necessary for production of steroid
hormones
Production of strong skin
Enhance immune system
Protection of cells from potential oxidative
damage
RDA (Recommended Dietary Allowances)
0～1year-old baby
35mg
1～10year-old child
45mg
11～14year-old child
50mg
Adult
60mg
Pregnant woman
More than 20mg
Woman feeding baby with milk
More than 40mg
Children require vitamin C as they need to grow up connective tissues and
repair wounds., adults have more connective tissues and so they should take in a
larger amount of vitamin C. Pregnant women take in vitamin C for the growth o
fetus. Women feeding baby with milk require vitamin C as to produce more milk,
moreover, milk also contain vitamin C as an nutrient for the baby for an ideal diet.
Deficiency diseases:
Bleeding gum
Wounds fails to heal
Loosening teeth
Bone broken easily
Internal bleeding
Easily attacked by pathogens
Unwilling to eat
Slow growth
Anemia
Heart disease
Scurvy
Connective tissue fibres fail to form
Sore mouth
Teeth fall out
Foreboding of deficiency:
Bleeding gum
Sudden bruise without wounds
Daily Uses:
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Production of skin keeper
Production of vitamin C tablets
As food additives
e.g. mild powder.
There are several remarks here:
Vitamin C
1. destroyed by boiling, especially in alkaline solution (∵ it is a acid);
2. soluble in water (∵ it is a acid), thus transported throughout the body by
blood. Blood also contain a small amount of vitamin C.
3. excess amount will be excreted out form the body and will not be stored;
4. easily excreted out form the body though urine and must, therefore, be
consumed regularly;
5. necessary for the mammals as they have to form connective tissues;
6. can be make by rats from other food in the diet;
7. have very little energy produce by combustion, thus is not treated as energy
source of daily diet;
8. carbon monoxide would denatured/malfunction vitamin C, so smokers must
take in more amounts of vitamin C.
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
In this experiment, the vitamin C content of the fruits is determined
titrimetrically and compared with other fruit.
Vitamin C is ascorbic acid which is rapidly and quantitatively oxidized by
iodine in acid soluiton according to the following equation:
Vitamin C decolorized iodine
when reacts with iodine according
to the eqn, H+ and I- and an acid salt
are formed.
Mechanism of formation of the acid salt (dehydroascorbate):
This standard method for determination of ascorbic acid involves the direct
titration of the acidified sample with a standard iodine solution. But the low
solubility of iodine makes this procedure less than ideal.
The proposed experiment avoids these difficulties by generating in situ a
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
known excess quantity of iodine by the reaction between iodate(V) and iodide:
IO3-(aq) + I-(aq) + 6H+(aq)  I2(aq) + 3H2O(l) + 4e2I-(aq) + 2e-  I2(aq)
x2
__________________________________________________________________________________
IO3-(aq) + 5I-(aq) + 6H+(aq)  3I2(aq) + 3H2O(l)
After reacting with ascorbic acid, the remaining iodine may then be titrated
against standard sodium thiosulphate solution. And the amount of ascorbic acid in
the fruit can be calculated.
2S2O32-(aq) + I2(aq)  S4O62-(aq) + 2I-(aq)
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Materials used
1. weighing bottle
2. balance ( + 0.0001g)
3. two 250ml beakers
4. glass rod
5. 100ml measuring cylinder
6. 250ml volumetric flask
7. 10cm3 burette
8. titration apparatus, stand and clip
9. knife, juice extractor
10. Bunsen burner, test tube, wood clip
11. filter paper (optional), filter funnel (optional)
12. Chemicals:
a. Fruits
b.
c.
d.
e.
f.
g.
Potassium iodate(V)
1M potassium iodide
0.5M sulphuric acid
0.05M sodium thiosulphate solution
Starch solution
deionized water
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Procedures
1. Measuring the mass of potassium iodate(V) used by ‘weigh by difference’
method
a. A balance was set zero after a weighing bottle was placed onto it.
b. 0.6-0.7g of potassium iodate(V) was transferred carefully into the bottle in
the balance.
c. The reading from the balance was recorded in Table 1.
d. The potassium iodate(V) was then transferred into a 250ml beaker.
e. Again the bottle with the residue was weighted.
f. The reading from the balance was recorded in Table 1.
2. Preparation of potassium iodate(V) solution
a. Deionized water was added into the 250ml beaker.
b. The solution was stirred with a glass rod until the solid potassium iodate(V)
was dissolved wholly.
c.
d.
e.
f.
The potassium iodate(V) solution was transferred into the 250ml
volumetric flask.
Deionized water was added until the minicus reachs the 250ml-line.
The flask was shaken for 2-3 minutes to mix the solution with the
deionized water.
The potassium iodate(V) solution mixture was transferred into the 250ml
beaker.
3. Standardization of the sodium thiosulphate solution
a. 25cm3 of the potassium iodate(V) solution was pipetted into a conical
flask.
b. About 10cm3 of 0.5M sulphuric acid was added into the flask and then
5cm3 of potassium iodide.
c. The solution was then titrated immediately with sodium thiosulphate
solution.
d. A few drops of starch solution was added when the reaction mixture turns
to pale yellow like this.
e.
f.
Then the mixture was titrated to the end point, which the solution would
become colorless.
The volume of sodium thiosulphate solution used to titrated was recorded
in Table 2.
4. Preparation of fruit juice
a. The fruit was cut into two pieces by a knife and the juice was extracted by
pressing them onto the juice extractor.
b. The juice was filtered with filter paper and filter funnel, but due to time
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
consuming, this step could be optional. And the residues of the fruit could
c.
d.
e.
f.
g.
be treated as error.
The juice was transferred to a clean 250ml volumetric flask.
150cm3 of 0.5M sulphuric acid was added into the solution by 100ml
measuring cylinder.
Deionized water was added until the minicus reachs the 250ml-line.
The flask was shaken for 2-3 minutes to mix the solution with the
deionized water.
The fruit juice mixture was transferred into a 250ml beaker.
5. Titration between the fruit juice mixture and the sodium thiosulphate
solution
a. 25cm3 of the fruit juice mixture was transferred to a clean conical flask by
a clean pipette.
b. 25cm3 of potassium iodate (V) solution mixture which had been prepared
c.
d.
e.
f.
was added into the flask and then 5cm3 of potassium iodide.
The solution was then titrated immediately with sodium thiosulphate
solution.
A few drops of starch solution was added when the reaction mixture turns
to pale yellow like this.
Then the mixture was titrated to the end point, which the solution would
become colorless.
The volume of sodium thiosulphate solution used to titrate was recorded in
Table 3.
6. Investigation of the other fruits
a. The previous steps were repeated but started with another fruit instead of
the previous fruit used.
b. The same thing was done as using other fruits.
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Results
1. Investigation of Mr.
JuiceTM
Orange Juice
Table 1, mass of potassium iodate(V) used to prepare primary standard potassium
iodate(V) solution.
Mass of potassium iodate(V) added
0.65g
Mass of weighing bottle with residue
0.00g
Mass of potassium iodate(V) used
0.65g
Table 2, titration between thiosulphate solution and potassium iodate(V) mixing
with potassium iodide and dilute sulphuric acid.
Final burette reading/cm3
Initial burette
reading/cm3
Volume of Na2S2O3/cm3
Trial
1st
2nd
38.0
37.25
37.23
0.2
0.0
0.0
37.8
37.25
37.23
37.43
Mean titre
Table 3, titration between thiosulphate solution and fruit juice mixing with
potassium iodide and dilute sulphuric acid.
Trial
1st
2nd
37.25
36.8
36.85
Initial burette reading/cm3 0.05
0.1
0.25
Volume of Na2S2O3/cm3
36.7
36.60
Final burette reading/cm3
37.20
36.83
Mean titre
Price: $ 26.9/1.5L
- 12 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Results
McDonald’sTM
2. Investigation of
Ketchup
Table 1, mass of potassium iodate(V) used to prepare primary standard potassium
iodate(V) solution.
Mass of potassium iodate(V) added
0.68g
Mass of weighing bottle with residue
0.15g
Mass of potassium iodate(V) used
0.65g
Table 2, titration between thiosulphate solution and potassium iodate(V) mixing
with potassium iodide and dilute sulphuric acid.
1st
2nd
Final burette reading/cm3
38.25
38.0
Initial burette reading/cm3
0.6
0.15
37.65
37.75
Trial
Volume of Na2S2O3
/cm3
37.70
Mean titre
Table 3, titration between thiosulphate solution and fruit juice mixing with
potassium iodide and dilute sulphuric acid.
1st
2nd
Final burette reading/cm3
33.7
33.4
Initial burette reading/cm3
0.3
0.1
Volume of Na2S2O3/cm3
33.4
33.3
Trial
33.35
Mean titre
3
3
3
* 34 cm ketchup, 150 cm H2SO4 50cm H2O was used;
* 50 cm3 of the fruit juice mixture was pipetted and used to titrate with
Na2S2O3.
Price: $ 0.0/packet
- 13 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Results
3. Investigation of Fresh Lemon
Table 1, mass of potassium iodate(V) used to prepare primary standard potassium
iodate(V) solution.
Mass of potassium iodate(V) added
0.662g
Mass of weighing bottle with residue
0.008g
Mass of potassium iodate(V) used
0.654g
Table 2, titration between thiosulphate solution and potassium iodate(V) mixing
with potassium iodide and dilute sulphuric acid.
Trial
Final burette reading/cm3
Initial burette
reading/cm3
Volume of Na2S2O3/cm3
1st
2nd
38.25
38.0
0.6
0.15
37.65
37.75
37.70
Mean titre
Table 3, titration between thiosulphate solution and fruit juice mixing with
potassium iodide and dilute sulphuric acid.
1st
2nd
Final burette reading/cm3
37.6
37.5
Initial burette reading/cm3
0.2
0.0
Volume of Na2S2O3/cm3
37.4
37.5
Trial
37.45
Mean titre
Price: $ 1.5/lemon
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Results
4. Investigation of the Same Lemon which was kept in refrigerator(~4oC) One
Week After
Table 1, mass of potassium iodate(V) used to prepare primary standard potassium
iodate(V) solution.
Mass of potassium iodate(V) added
0.68g
Mass of weighing bottle with residue
0.15g
Mass of potassium iodate(V) used
0.65g
Table 2, titration between thiosulphate solution and potassium iodate(V) mixing
with potassium iodide and dilute sulphuric acid.
Trial
Final burette reading/cm3
Initial burette
reading/cm3
Volume of Na2S2O3/cm3
1st
2nd
38.25
38.0
0.6
0.15
37.65
37.75
37.70
Mean titre
Table 3, titration between thiosulphate solution and fruit juice mixing with
potassium iodide and dilute sulphuric acid.
1st
2nd
Final burette reading/cm3
37.65
37.6
Initial burette reading/cm3
0.2
0.0
Volume of Na2S2O3/cm3
37.45
37.6
Trial
37.53
Mean titre
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Results
5. Investigation of
*YourLife®
Vitamin C Tablet
Table 1, mass of potassium iodate(V) used to prepare primary standard potassium
iodate(V) solution.
Mass of potassium iodate(V) added
0.68g
Mass of weighing bottle with residue
0.15g
Mass of potassium iodate(V) used
0.65g
Table 2, titration between thiosulphate solution and potassium iodate(V) mixing
with potassium iodide and dilute sulphuric acid.
Trial
Final burette reading/cm3
Initial burette
reading/cm3
Volume of Na2S2O3/cm3
1st
2nd
33.50
33.55
0.05
0.1
33.45
33.45
33.45
Mean titre
Table 3, titration between thiosulphate solution and fruit juice mixing with
potassium iodide and dilute sulphuric acid.
Trial
1st
2nd
27.3
26.3
26.2
Initial burette reading/cm3 0.0
0.3
0.2
Volume of Na2S2O3/cm3
26.0
26.0
Final burette reading/cm3
27.3
26.43
Mean titre
* The investigation of YourLife® Vitamin C Tablet acted as a control experiment.
* The procedures of the Preparation of YourLife® Vitamin C Tablet solution
were different from those of the Preparation of fruit juice:
Preparation of YourLife® Vitamin C Tablet solution:
a. The tablet was dissolved in 150cm3 of 0.5M sulphuric acid in a 250ml
beaker.
b. The resulting solution was transferred to a clean 250ml volumetric flask.
c. Deionized water was added until the minicus reachs the 250ml-line.
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
d.
The flask was shaken for 2-3 minutes to mix the solution with the
e.
deionized water.
The solution mixture was transferred into a 250ml beaker.
Then the other procedures were the same as the part of the Procedures mentioned
before.
- 17 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Data Analysis
1.
Investigation of Mr.
JuiceTM
Orange Juice
Mass of potassium iodate(V) used
0.65g
Mean volume of Na2S2O3 used to titrate
KIO3 with KI and dil. H2SO4
37.43 cm3
Mean volume of Na2S2O3 used to titrate
fruit juice with KI and dil. H2SO4
36.83 cm3
a. Calculate the concentration of the given sodium thiosulphate solution:
Molar mass of KIO3
39.10 + 126.90 + 16.00 x 3
= 214.00g
Mass of potassium iodate(V) used
0.65g
no. of moles of KIO3
0.65
25

214.0 250
= 3.037 x 10-4
IO3-(aq) + 5I-(aq) + 6H+(aq)  3I2(aq) + 3H2O(l)
∴ 1 mole of KIO3 forms 3 moles of I2
3 x 3.037 x 10-4
= 9.112 x 10-4
no. of mole of iodine produced
2S2O32-(aq) + I2(aq)  S4O62-(aq) + 2I-(aq)
∴ 1 mole of I2 reacts with 2 moles of S2SO32no. of mole of S2SO32- reacted
2 x 9.112 x 10-4
= 1.822 x 10-3
Mean volume of Na2S2O3 used to
titrate KIO3 with KI and dil. H2SO4
37.43 cm3
Concentration of the given Na2S2O3
1.822  10 -3
37.43
1000
= 4.869 x 10-2 mol dm-3
b. Calculate the concentration of vitamin C in Mr. JuiceTM Orange Juice:
Since same no. of mole of KIO3 is used for titration in part 1 amd 3, the
difference of the volume of Na2S2O3 used can be used to calculate the no. of
mole of vitamin C reacted.
Mean volume of Na2S2O3 used to
titrate fruit juice with KI and dil.
H2SO4
36.83 cm3
Concentration of the given Na2S2O3
4.869 x 10-2 mol dm-3
no. of moles of S2O3+2- used to titrate
fruit juice with KI and dil. H2SO4
- 18 -
4.869  10 -2 
36.83
1000
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
= 1.793 x 10-3
2S2O32-(aq) + I2(aq)  S4O62-(aq) + 2I-(aq)
∴ 1 mole of I2 reacts with 2 moles of S2SO32no. of moles of I2 remained after
reacting vitamin C and I2
1.793  10 -3
2
= 8.966 x 10-4
Mass of potassium iodate(V) used
0.65g
no. of moles of I2 produced
3
0.65
25

214.0 250
= 9.112 x 10-4
no. of moles of I2 reacted with vitamin 9.112 x 10-4 - 8.966 x 10-4
C
= 1.461 x 10-5
∴ 1 mole of ascorbic acid (vitamin C) reacts with 1 mole of I2 produced form
KIO3
1.461 x 10-5
no. of moles if vitamin C reacted
Volume of each bottle of Mr. JuiceTM 2.4L = 2400 cm3
Orange Juice
no. of moles of vitamin C contained in
Mr. JuiceTM Orange Juice
1.461 10 5
25
2400
= 1.402 x 10-3
c. Amount of vitamin C that will be bought if $ 1.00 is paid:
no. of moles of vitamin C contained in 1.402 x 10-3
Mr. JuiceTM Orange Juice
Normal price of Mr. JuiceTM Orange $ 26.9/2.4L
Juice
1.402  10-3
$26.9
= 5.210 x 10-5 mol
Amount of vitamin C that will be
bought if $ 1.00 is paid
d. Price to buy 1 mol of vitamin C:
no. of moles of vitamin C contained in 1.402 x 10-3
Mr. JuiceTM Orange Juice
Normal price of Mr. JuiceTM Orange $ 26.9/2.4L
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Juice
Price to buy 1 mole of vitamin C:
$ 26.9
1.402  10 -3
= $ 1.919 x 104
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Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
2.
by K. F. Leung
Investigation of Mcdonald’sTM Ketchup:
Mass of potassium iodate(V) used
0.65g
Mean volume of Na2S2O3 used to titrate
KIO3 with KI and dil. H2SO4
37.70 cm3
Mean volume of Na2S2O3 used to titrate
fruit juice with KI and dil. H2SO4
33.35 cm3
* 34 cm3 ketchup, 150 cm3 H2SO4 50cm3 H2O was used;
* 50 cm3 of the fruit juice mixture was pipetted and used to titrate with Na2S2O3.
a. Calculate the concentration of the given sodium thiosulphate solution:
Molar mass of KIO3
39.10 + 126.90 + 16.00 x 3
= 214.00g
Mass of potassium iodate(V) used
0.65g
no. of moles of KIO3
0.65
25

214.0 250
= 3.037 x 10-4
IO3-(aq) + 5I-(aq) + 6H+(aq)  3I2(aq) + 3H2O(l)
∴ 1 mole of KIO3 forms 3 moles of I2
3 x 3.037 x 10-4
= 9.112 x 10-4
no. of mole of iodine produced
2S2O32-(aq) + I2(aq)  S4O62-(aq) + 2I-(aq)
∴ 1 mole of I2 reacts with 2 moles of S2SO32no. of mole of S2SO32- reacted
2 x 9.112 x 10-4
= 1.822 x 10-3
Mean volume of Na2S2O3 used to
titrate KIO3 with KI and dil. H2SO4
37.70 cm3
Concentration of the given Na2S2O3
1.822  10 -3
37.70
1000
= 4.834 x 10-2 mol dm-3
b. Calculate the concentration of vitamin C in Mcdonald’sTM Ketchup:
Since same no. of mole of KIO3 is used for titration in part 1 amd 3, the
difference of the volume of Na2S2O3 used can be used to calculate the no. of
mole of vitamin C reacted.
Mean volume of Na2S2O3 used to
titrate fruit juice with KI and dil.
H2SO4
33.35 cm3
Concentration of the given Na2S2O3
4.834 x 10-2 mol dm-3
- 21 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
no. of moles of S2O3+2- used to titrate
fruit juice with KI and dil. H2SO4
4.834  10 -2 
33.35
1000
= 1.612 x 10-3
2S2O32-(aq) + I2(aq)  S4O62-(aq) + 2I-(aq)
∴ 1 mole of I2 reacts with 2 moles of S2SO32no. of moles of I2 remained after
reacting vitamin C and I2
1.612  10 -3
2
= 8.061 x 10-4
Mass of potassium iodate(V) used
0.65g
no. of moles of I2 produced
3
0.65
25

214.0 250
= 9.112 x 10-4
no. of moles of I2 reacted with vitamin 9.112 x 10-4 - 8.061 x 10-4
C
= 1.051 x 10-4
∴ 1 mole of ascorbic acid (vitamin C) reacts with 1 mole of I2 produced form
KIO3
1.051 x 10-4
no. of moles if vitamin C reacted
Since 10 packets (34cm3) of Mcdonald’sTM Ketchup was used.
Volume of each packet of
Mcdonald’sTM
34
= 3.4 cm3
10
Ketchup
Since 50cm3 of the fruit juice mixture was used to titrate with Na2S2O3.
no. of moles of vitamin C contained in
each Mcdonald’sTM Ketchup
1.1051  10 5
 10
50
34
= 7.150 x 10-6
c. Numbers of packet of Mr. JuiceTM Orange Juice to get 1 mol of vitamin C:
no. of moles of vitamin C contained in
7.150 x 10-6
Mr. JuiceTM Orange Juice
Numbers of packet to get 1 mol of
vitamin C
1
7.150  10 -6
= 1.399 x 105 packets
- 22 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
3.
by K. F. Leung
Investigation of Fresh Lemon
Mass of potassium iodate(V) used
0.654g
Mean volume of Na2S2O3 used to titrate
KIO3 with KI and dil. H2SO4
37.70 cm3
Mean volume of Na2S2O3 used to titrate
fruit juice with KI and dil. H2SO4
37.45 cm3
a. Calculate the concentration of the given sodium thiosulphate solution:
Molar mass of KIO3
39.10 + 126.90 + 16.00 x 3
= 214.00g
Mass of potassium iodate(V) used
0.654g
no. of moles of KIO3
0.654 25

214.0 250
= 3.056 x 10-4
IO3-(aq) + 5I-(aq) + 6H+(aq)  3I2(aq) + 3H2O(l)
∴ 1 mole of KIO3 forms 3 moles of I2
3 x 3.056 x 10-4
= 9.168 x 10-4
no. of mole of iodine produced
2S2O32-(aq) + I2(aq)  S4O62-(aq) + 2I-(aq)
∴ 1 mole of I2 reacts with 2 moles of S2SO32no. of mole of S2SO32- reacted
2 x 9.168 x 10-4
= 1.834 x 10-3
Mean volume of Na2S2O3 used to
titrate KIO3 with KI and dil. H2SO4
37.70 cm3
Concentration of the given Na2S2O3
1.834  10 -3
37.70
1000
= 4.864 x 10-2 mol dm-3
b. Calculate the concentration of vitamin C in Fresh Lemon:
Since same no. of mole of KIO3 is used for titration in part 1 amd 3, the
difference of the volume of Na2S2O3 used can be used to calculate the no. of
mole of vitamin C reacted.
- 23 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
37.45 cm3
Mean volume of Na2S2O3 used to
titrate fruit juice with KI and dil.
H2SO4
Concentration of the given Na2S2O3
no. of moles of S2O3+2- used to titrate
fruit juice with KI and dil. H2SO4
4.864 x 10-2 mol dm-3
4.864  10 -2 
37.45
1000
= 1.821 x 10-3
2S2O32-(aq) + I2(aq)  S4O62-(aq) + 2I-(aq)
∴ 1 mole of I2 reacts with 2 moles of S2SO32reacting vitamin C and I2
1.82  10 -3
2
= 9.107 x 10-4
Mass of potassium iodate(V) used
0.654g
no. of moles of I2 remained after
no. of moles of I2 produced
3
0.654 25

214.0 250
= 9.168 x 10-4
no. of moles of I2 reacted with vitamin 9.112 x 10-4 - 8.966 x 10-4
C
= 6.080 x 10-6
∴ 1 mole of ascorbic acid (vitamin C) reacts with 1 mole of I2 produced form
KIO3
no. of moles if vitamin C reacted
6.080 x 10-6
Volume of juice each Fresh Lemon
obtained
28cm3
no. of moles of vitamin C contained in
Fresh Lemon
6.080  10 6
25
28
= 6.809 x 10-6
c. Amount of vitamin C that will be bought if $ 1.00 is paid:
no. of moles of vitamin C contained in
6.809 x 10-6
Fresh Lemon
$ 1.5/lemon
Normal price of Fresh Lemon
6.809  10 -6
$1.5
Amount of vitamin C that will be
bought if $ 1.00 is paid
- 24 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
= 4.540 x 10-6 mol/dollar
d. Price to buy 1 mol of vitamin C:
no. of moles of vitamin C contained in
6.809 x 10-6
Fresh Lemon
$ 1.5/lemon
Normal price of Fresh Lemon
Price to buy 1 mole of vitamin C:
$ 1.5
6.809  10 -6
= $ 2.203 x 105
- 25 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
4.
by K. F. Leung
Investigation of Same Lemon One Week After keeping in 4oC
Mass of potassium iodate(V) used
0.65g
Mean volume of Na2S2O3 used to titrate
KIO3 with KI and dil. H2SO4
37.70 cm3
Mean volume of Na2S2O3 used to titrate
fruit juice with KI and dil. H2SO4
37.53 cm3
a. Calculate the concentration of the given sodium thiosulphate solution:
Molar mass of KIO3
39.10 + 126.90 + 16.00 x 3
= 214.00g
Mass of potassium iodate(V) used
0.654g
no. of moles of KIO3
0.65
25

214.0 250
= 3.037 x 10-4
IO3-(aq) + 5I-(aq) + 6H+(aq)  3I2(aq) + 3H2O(l)
∴ 1 mole of KIO3 forms 3 moles of I2
3 x 3.037 x 10-4
= 9.112 x 10-4
no. of mole of iodine produced
2S2O32-(aq) + I2(aq)  S4O62-(aq) + 2I-(aq)
∴ 1 mole of I2 reacts with 2 moles of S2SO32no. of mole of S2SO32- reacted
2 x 9.112 x 10-4
= 1.822 x 10-3
Mean volume of Na2S2O3 used to
titrate KIO3 with KI and dil. H2SO4
Concentration of the given Na2S2O3
37.70 cm3
1.822  10 -3
37.70
1000
= 4.834 x 10-2 mol dm-3
b. Calculate the concentration of vitamin C in Same Lemon One Week After:
Since same no. of mole of KIO3 is used for titration in part 1 amd 3, the
difference of the volume of Na2S2O3 used can be used to calculate the no. of
mole of vitamin C reacted.
Mean volume of Na2S2O3 used to
titrate fruit juice with KI and dil.
H2SO4
37.53 cm3
Concentration of the given Na2S2O3
4.834 x 10-2 mol dm-3
no. of moles of S2O3+2- used to titrate
fruit juice with KI and dil. H2SO4
4.834  10 -2 
= 1.814 x 10-3
- 26 -
37.53
1000
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
2S2O32-(aq) + I2(aq)  S4O62-(aq) + 2I-(aq)
∴ 1 mole of I2 reacts with 2 moles of S2SO32no. of moles of I2 remained after
reacting vitamin C and I2
1.82  10 -3
2
= 9.071 x 10-4
Mass of potassium iodate(V) used
0.65g
no. of moles of I2 produced
3
0.65
25

214.0 250
= 9.112 x 10-4
no. of moles of I2 reacted with vitamin
9.112 x 10-4 – 9.071 x 10-4
= 4.109 x 10-6
C
∴ 1 mole of ascorbic acid (vitamin C) reacts with 1 mole of I2 produced form
KIO3
no. of moles if vitamin C reacted
4.109 x 10-6
c. Amount of vitamin C lost due to oxidation by air in 4℃:
no. of moles of vitamin C contained in 6.809 x 10-6
Fresh Lemon (by result of
Investigation of Fresh Lemon)
no. of moles of Same Lemon One
Week After:
4.109 x 10-6
% Loss of vitamin C
6.809  10 6  4.109  10 6
 100%
6.809  10 6
= 39.65%
- 27 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
5.
by K. F. Leung
Investigation of YourLife® Vitamin C Tablet
Mass of potassium iodate(V) used
0.65g
Mean volume of Na2S2O3 used to titrate
KIO3 with KI and dil. H2SO4
33.45 cm3
Mean volume of Na2S2O3 used to titrate
fruit juice with KI and dil. H2SO4
26.43 cm3
a. Calculate the concentration of the given sodium thiosulphate solution:
Molar mass of KIO3
39.10 + 126.90 + 16.00 x 3
= 214.00g
Mass of potassium iodate(V) used
0.65g
no. of moles of KIO3
0.65
25

214.0 250
= 3.037 x 10-4
IO3-(aq) + 5I-(aq) + 6H+(aq)  3I2(aq) + 3H2O(l)
∴ 1 mole of KIO3 forms 3 moles of I2
3 x 3.037 x 10-4
= 9.112 x 10-4
no. of mole of iodine produced
2S2O32-(aq) + I2(aq)  S4O62-(aq) + 2I-(aq)
∴ 1 mole of I2 reacts with 2 moles of S2SO32no. of mole of S2SO32- reacted
2 x 9.112 x 10-4
= 1.822 x 10-3
Mean volume of Na2S2O3 used to
titrate KIO3 with KI and dil. H2SO4
Concentration of the given Na2S2O3
33.45 cm3
1.822  10 -3
33.45
1000
= 5.448 x 10-2 mol dm-3
b. Calculate the concentration of vitamin C in YourLife® Vitamin C Tablet:
Since same no. of mole of KIO3 is used for titration in part 1 amd 3, the
difference of the volume of Na2S2O3 used can be used to calculate the no. of
mole of vitamin C reacted.
Mean volume of Na2S2O3 used to
titrate fruit juice with KI and dil.
H2SO4
26.43 cm3
Concentration of the given Na2S2O3
5.448 x 10-2 mol dm-3
no. of moles of S2O3+2- used to titrate
fruit juice with KI and dil. H2SO4
5.448  10 -2 
= 1.440 x 10-3
- 28 -
26.43
1000
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
2S2O32-(aq) + I2(aq)  S4O62-(aq) + 2I-(aq)
∴ 1 mole of I2 reacts with 2 moles of S2SO32no. of moles of I2 remained after
reacting vitamin C and I2
1.440  10 -3
2
= 7.200 x 10-4
Mass of potassium iodate(V) used
0.65g
no. of moles of I2 produced
3
0.65
25

214.0 250
= 9.112 x 10-4
9.112 x 10-4 – 7.200 x 10-4
no. of moles of I2 reacted with vitamin
= 1.912 x 10-4
C
∴ 1 mole of ascorbic acid (vitamin C) reacts with 1 mole of I2 produced form
KIO3
1.912 x 10-4
no. of moles if vitamin C reacted
c. Mass of vitamin C per YourLife® Vitamin C Tablet
1.912  10 -4 
no. of moles of vitamin C in each
YourLife® Vitamin C Tablet
=
1.912 x 10-3
Molar mass of vitamin C (ascorbic
acid)
12.0 x 6 + 16.0 x 6 + 1.0 x 8
= 176.0g
Mass of vitamin C per YourLife®
1.912 x 10-3- x 176.0
= 0.3366g
Vitamin C Tablet
d.
250
25
Price to buy 1 mole vitamin C:
$ 85/100tablets
Price of each bottle of YourLife®
Vitamin C Tablet
Price to buy 1 YourLife® Vitamin C
Tablet
$ 85
100
= $ 0.85
1.912 x 10-3
no. of moles of vitamin C in each
YourLife® Vitamin C Tablet
Price to buy 1 mole of vitamin C
$ 0.85
1.912  10 -3
= $ 4.446 x 102
- 29 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
e. Amount of vitamin C will be obtained if $1 was paid:
1.912 x 10-3
no. of moles of vitamin C in each
YourLife® YourLife® Vitamin C
Tablet
Price to buy 1 YourLife® YourLife® $ 0.85
Vitamin C Tablet
Amount of vitamin C will be obtained
if $1 was paid:
1.912  10 3
0.85
= 2.249 x 10-3 mol
f. Comparison between the amount of vitamin C per YourLife® Vitamin C
Tablet of manufacture prescribed and the experiment result:
Manufacturer’s specification of the
amount of vitamin C in YourLife®
Vitamin C Tablet
500mg per tablet
1.912 x 10-3- x 176.0
= 0.3366g
Vitamin C Tablet
∴ The amount of vitamin C found in the experiment is less than the
Mass of vitamin C per YourLife®
manufacture’s prescribe.
- 30 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Conclusion
To compare which type of fruit is best buy with respect to the vitamin C content
Amount of vitamin C in Mr. JuiceTM
Orange Juice that will be bought if $
1.00 is paid
5.210 x 10-5 mol
Amount of vitamin C in Fresh Lemon 4.540 x 10-6 mol
that will be bought if $ 1.00 is paid
Amount of vitamin C in YouLife®
Vitamin C Tablet will be obtained if
$1 was paid:
2.249 x 10-3 mol
Price to buy 1 mole of vitamin C: in
$ 1.919 x 104
Mr. JuiceTM Orange Juice
Price to buy 1 mole of vitamin C in
$ 2.203 x 105
Fresh Lemon
Price to buy 1 mole of vitamin C in
$ 4.446 x 102
YouLife® Vitamin C Tablet
no. of moles of vitamin C contained in 1.402 x 10-3
each 2.4L bottle of Mr. JuiceTM
Orange Juice
no. of moles of vitamin C contained in 7.150 x 10-6
each Mcdonald’sTM Ketchup
1.912 x 10-3
no. of moles of vitamin C in each
YourLife® Vitamin C Tablet
% Loss of vitamin C of Same Lemon 39.65%
One Week After in 4oC
- 31 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Discussion
1. Why it is called vitamin C as ‘ascorbic acid’?
The structure of vitamin C:
which contains a –COOH group, an acid group. Thus it is an acid. The term
‘ascorbic’ is from ‘scurvy’. Due to vitamin C is a medicine to scurvy, so it was
called ascorbic acid.
2. The sodium thiosulphate must be standardized first, explain what is meant by
‘standardized’.
Use a primary standard (KIO3) to find out the accurate molarity of a substance
which cannot be used as a primary standard.
3. State the function of the starch solution, explain why it should be added only
when the reaction mixture becomes pale yellow.
Starch solution acts as an indicator to indicate the end point of titration.
It should be added only when the reaction mixture becomes pale yellow. It is
because if it is added too early, the concentration of iodine is so high that it will
react with iodine to form a water insoluble complex. As a result, the amount of
iodine available for reacting with sodium thiosulphate becomes smaller.
4. After the addition of sulphuric acid to the reaction mixture, what would happen
if titration is not carried out immediately?
After the amount of sulphuric acid to the reaction mixture, iodine is formed. It
will vaporize and the amount of iodine available for reacting with sodium
thiosulphate becomes smaller.
In addition, iodide ions in the reaction mixture will be oxidized by oxygen gas in
air as shown in the following equation:
4I-(aq) + O2(g) + 4H+(aq)  2I2(aq) + 2H2O(l)
Thus more iodine is available for reacting with sodium thiosulphate.
5. Why the result of calculating the concentration of vitamin C in the Mr. JuiceTM
Orange Juice is different, though the same bottle of the juice was used, form the
other classmates?
Although the same bottle of the juice, the classmates having the investigation
were at different time. Because vitamin C is a reducing agent, which will reduce
oxygen in air.
4H+(aq) + O2(g)  2H2O(l)
And so the amount of vitamin C decreased with time.
- 32 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
6. Account for the different of the amount of vitamin C in Investigation of
YourLife® Vitamin C Tablet which is smaller than that of as prescribed.
The amount of vitamin C in Investigation of YourLife® Vitamin C Tablet
which is smaller than that of as prescribed because there were some errors
during the experiment:
a. Some undissolved Vitaminn C Tablet remained in the beaker as the solution
became saturated.
b. Some vitamin C solution split out during transferring.
c. The accuracy of the titre.
d. Since the tablets contains additives, (namely, the ingredients: ascorbic acid,
strach, crospovidone, cellulose, magnesium stearate, stearic acid,
croscarmellose sodium, silicon dioxide, lactose) in which, e.g. starch will
affect the end point of the titration with Na2S2O3 certainly.
7. Besides decomposition by air, what other factors may also affect the
concentration of vitamin C?
a. Humidity: vitamin C is an acid which is very water soluble. If the humidity is
very high, the vitamin C will be dissolved away by the water vapours in the
air.
b. Temperature: vitamin C has an unstable structure. If strong heating is applied,
the vitamin C would be decomposed
8. Account for the low amount of vitamin C concentration in the Fresh Lemon.
The low concentration calculated from the Fresh Lemon may be due to
a.
The old lemon was used. Since the vitamin C in old lemon would certainly
decomposed by the air already, the concentration of vitamin C found was
low.
b. The juice after extraction was placing for a long time that enough for the
serious decomposition by the air. It was calculated that even the juice was
kept in 4oC for one week, 39.65% of vitamin C was loss.
- 33 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
c.
by K. F. Leung
Error Analysis
1. The residues of the orange inside the sample.
2. The undissolved YourLife® Vitamin C Tablet in the sample.
3. Flouring or coloring additives were added into the juice and disturbed the
observation and even the titre.
- 34 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Precautions
1. Potassium iodate(V) and 0.5M sulphuric acid should be handled carefully as the
former is oxidizing, the later is irritant.
2. Therefore, goggles should be worn.
3. Starch solution should be freshly prepared, otherwise amylase of the bacteria
around the air may digest the starch into maltose or glucose, the starch solution
may be dilute and cannot be an indicator.
4. Starch solution was added after the reaction mixture becomes pale yellow.
5. The titration should be carried out quickly after preparation, since iodide is a
strong reducing agent which will be oxidized by the air.
6. The potassium iodate(V) solution can be stored bo use after one week but the
juices cannot because the former was primary standard while the later was
changing its concentration, i.e. vitamin C were oxidizing continually by the air
even though keeping in refrigerator,
7. Clean conical flask and titration apparatus should be used to minimize the errors.
- 35 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Related web-links
1. http://members.aol.com/citrusweb/oj_story.html ---- provides information on the
effect of the fruit in different environment, e.g. temperature, sunlight, humidity
etc.
2. http://www.wedar.com/library/lib10-4.htm ---- a Chinese website provides
information of vitamin C.
3. http://business.fortunecity.com/gap/185/c.htm ---- a Chinese website provides
information of vitamin C.
4. http://www.positivehealth.com/permit/Articles/Nutrition/vitcbiblio.htm ---- a
website provides information of vitamin C.
5. http://www.mfbmclct.edu.hk/~chemistry/HKAL1.htm ---- a website provides
information of vitamin C.
6. http://nutri.tmc.edu.tw/networks/ ---- a website contains a large amount of
medical information as well as the uses of vitamin C.
7. http://www.wedar.com/library.htm ---- a websites contains medical Q&A as well
as vitamin C.
- 36 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
News Scripts About Vitamin C
- 37 -
Chemistry TAS Project
Project on Analysis of Vitamin C in Fruit
by K. F. Leung
Name: Leung Kam Fai
Class: 6S
Class no.: 11
Email: cartoon_lkf@sinatown.com
ICQ no.: 94788200
- 38 -