The amount of vitamin C in grapefruit juice and apple juice
Engels, L., & Nicolai, A.
Gymnasium Haganum Den Haag, The Netherlands
Received march 2009
Vitamin C can be found in a lot of fruits. It’s very important for a human being to get
enough vitamin C in the body, if you don’t get enough vitamin C in you body per day;
you are risking deceases like scurvy. In contrast to a lot of animals, human beings
cannot make there own amount of vitamin C in their body.
The question of this experiment is in which juice the biggest amount of vitamin C is
concentrated. The hypothesis is that the amount of vitamin C is bigger in grapefruit
juice than in apple juice.
Vitamin C, or ascorbic acid, is a very The amount of vitamin C is findable
important vitamin for a human being. when it’s titrated with a solution of KIO3
A deficiency in vitamin C causes If you add a bit of starch and sulphuric
scurvy, a notorious decease for sailors acid the mixture will turn in to a
during long routes, which used to afflict black/blue solution. The question
the V.O.C. during the 17th century. arises which mixture (apple juice or
Vitamin C is essential for a good grapefruit juice) will turn into a
resistance, and helps to build bones, blue/black solution first. Therefore is
teeth and veins. Vitamin C is also an the question for the experiment:
antioxidant, and protects the body Which juice contains the biggest
against the reaction between other amount of vitamin C, grapefruit juice or
matter and free radicals in oxygen, apple juice?
which causes the aging process. Our hypothesis is that apple juice will
Animals can produce their own amount turn into a blue suspension first, so the
of vitamin C, all animals but chimps, grapefruit juice contains the most
guinea pigs and human beings. vitamin C.
Since the time of the hunter-gatherer, This is based on the theory of S.K. Lee
people started to eat fruits and eatable and A.A. Kader that says, that the
plants. These fruits consist of vitamin C temperature of the place where the
and today it’s still recommended to eat fruit grows has influence on the
two pieces of fruit to maintain the level amount of vitamin C found in this fruit.
of vitamin C in your body.
The molecular formula of vitamin C is Experimental procedure and
C6H8O6 (see figure 1). approach
To start, begin with cleaning everything
with distilled water. When everything is
thoroughly clean, fill the burette with
KIO3(aq) (0,0050M) . After this, fill the
pipette of 25 mL with apple juice. The
apple juice consisted extra vitamin C
as seen on the packing. When the
pipette is filled with 25 mL of apple
juice, put it in the erlenmeyer. Also add
a bit of starch- solution (C6H10O5)n
Figure 1: structure of vitamin C
(aq)) and sulphuric acid (H2SO4 (aq)). Apple juice KIO3-(aq)
Then fill another pipette, this time one mixture (mL)
of 10 mL, with a solution of KI and add (mL)
this too, to the erlenmeyer. Now the 25,00 3,40
titration can begin. Carefully the KIO3 25,00 3,30
(aq) of the burette is dripped in to the Average: 25,00 3,35
erlenmeyer until there is a changing of Table 1: the results of the KIO3-(aq) (mL)
color to blue/black. This change of in the two titrations of 25.00 mL Apple
color is caused when the vitamin C has juice mixture.
reacted with I2 (aq) (see reaction 2)
and the starch comes in touch with the Grapefruit juice KIO3-(aq)
I2. This I2 arises when the reaction mixture (mL)
between IO3- (aq) and I- (aq) has taken (mL)
place (see reaction 1). 25,00 4,33
-Reaction 1 Average: 25,00 4,22
IO3- (aq) + 5I- (aq) +6H+ (aq) 3I2 (aq) Table 2: the results of the KIO3-(aq)
+ 3H2O(l) (mL) in the two titrations of 25,00 mL
Grapefruit juice mixture.
C6H8O6 (aq) + I2 (aq) C6H6O6 (aq) + Data analysis
2H+ (aq) + 2I-(aq) The 25,00 mL solutions of the apple
juice mixture and the grapefruit juice
Repeat the same experiment with mixture were titrated with 0,0050 mol/L
grapefruit juice. KIO3-(aq).
To start with apple juice, table 1 shows
that an average of 3,35 mL is
necessary for a color change. So the
calculations with the average amounts
conclude: 3,35 mL x 0,0050 mmol/mL
= 0,01675 mmol C6H8O6. Because IO3-
and I2 react in a ratio of 1:3 and
C6H8O6 and I2 in a ratio of 1:1.
C6H8O6 has a molecular weight of
176,13 g/mol so in 25 mL of apple juice
Figure 2: experimental set-up
there are 0,01675 x 176,13 = 2,95 mg
C6H8O6. In 100 mL there are 2,95 x 4 =
11,8 mg C6H8O6.
During the titration of the KIO3- solution
with the apple juice mixture the
The grapefruit juice, as shown in table
indicator changed color from goldish
2, has an average of 4,22 mL, which is
yellow to black/dark blue. Table 1
needed for a color change.
shows the results of the two
4,22 mL x 0,0050 mmol/mL = 0,0211
measurements with apple juice. Table
2 shows de results of the two
25 mL of grapefruit juice has 0,0211 x
measurements with grapefruit juice.
176,13 = 3,72 mg of C6H8O6. In 100
When the grapefruit juice was the
mL there are 3,72 x 4 = 14,9 mg
same blue color as the apple juice after
the titration, the titration of grapefruit
juice was finished.
with more pieces of different fruit from
There might be slight errors in the
measurements, because the
experiment is done by hand and this
means that there is an inaccuracy.
It is also hard to decide which color of
dark blue is the right one. So it’s hard
to say when all the vitamin C has
reacted with the I2.
Figure 3: the calibration curve. To have a good experiment there is
need of more kinds of juices, so the
In de calibration curve, you can see apple juices could be compared to
different amounts of vitamin C and the each other and a few grapefruit juices
need of KIO3-(aq) to turn the solution to each other, before comparing the
into blue/black. apple juice with the grapefruit juice,
This calibration curve is obtained from because there might be a lot of
an experiment that the teacher has differences between two kinds of apple
done. This curve has nothing to do with juices. But still the hypothesis was right
our own experiment, but indicates the and the experimental question is
regular reaction between C6H8O6 and answered. So, grapefruit juice contains
the biggest amount of vitamin C.
Conclusion and discussion
Mixture Moles Milligrams
As shown in the calculations there is a
(mL) C6H8O6 C6H8O6 in
bigger amount of vitamin C in
in 25,00 100 mL
grapefruit juice than in apple juice.
The measurements of the calibration
Apple 0,01675 11,80071
curve have been measured only once.
The reason for this is a shortage of
Grapefruit 0,0211 14,865372
In table 3, the results of the titrations
can be found. Here you can see that Table 3: Moles of C6H8O6 in 25,00 mL
and milligrams C6H8O6 in 100 mL in apple-
there is much more C6H8O6 in and grapefruit juice.
grapefruit juice than in apple juice.
These results support the hypothesis in It is well known that grapefruit contains
the affirmative. It also supports the more vitamin C than apple, so that is
theory of S.K. Lee and A.A. Kader. why the grapefruit juice also contains
The theory says that fruits that grow in more than the apple juice.
higher temperatures contain more It would be more relevant to find out in
vitamin C and the experiment confirms another experiment how much the
this, because grapefruits grow in a amount of vitamin C decreases when a
warmer climate than apples. fruit is made into a juice.
Of course two pieces of fruit aren’t What’s more, how much vitamin C
enough to conclude that the theory of disappears when a fruit is fabricated
S.K. Lee and A.A. Kader is right. into a juice? And contains fresh juice
If we want to prove that that theory is more vitamin C than fabricated vitamin
right we have to do this experiment C?
Bibliography horticultural crops: S.K. Lee, A.A.
http://www.vitamine-info.nl/vitamine_c 5. Buil, S. ir., (2009). Explanation and
2. stencils. The Hague: Gymnasium
3. http://en.wikipedia.org/wiki/Titration 6. Verkerk, G. dr., (a.o.) (2004). Binas,
4. Preharvest and postharvest factors table 82A, Groningen: Wolters
influencing vitamin C content of Noordhoff.