Candidate code: jmd730
Session: May 2021
The effect of temperature on Vitamin C content In Oranges and Kiwis
1: Introduction
Over the past few months, one new activity that I have thoroughly enjoyed doing is cooking.
During my pastime, I would watch videos detailing recipes of dishes, and I would then try cooking
them. More recently, I have been rather intrigued by dishes that contain fruits, as it was
something that I found unique. In particular, two dishes that grabbed my attention were “Orange
chicken pot with rice” and “Baked kiwi tart”, both fruits that are known for containing a high
amount of Vitamin C.
An article that I came across a while ago highlighted the degradation of Vitamin C which was
caused by exposure to heat. This article sparked my curiosity, as the aforementioned dishes with
fruits which I took interest in were required to be cooked at high temperatures. This led me to
question the effect of temperature on Vitamin C content. Inspired by this, when I came across the
chance to investigate the relationship between Vitamin C content and its effect due to increasing
temperatures through the chemistry internal assessment, I opted on the following research
question;
How do increasing temperatures (25.0℃, 40.0℃,55.0℃, 70.0℃, 85.0℃) affect the Vitamin C
content (mg) of oranges and kiwis; determined by redox titration using iodate solution?
2: Background Information
Vitamin C, also known as Ascorbic acid (C₆H₈O₆) is an essential nutrient in the human diet. The
recommended amount of Vitamin C intake for adults is between 60 mg to 95 mg per day. (Snyder,
2019) Vitamin C is extremely significant as it is needed for the growth of body tissues and is used
to prevent and also treat scurvy. Usually, a raw orange contains 0.5mg of Vitamin C per gram,
while a kiwi contains 0.9mg of Vitamin C per gram. (NutritionValue.Org, n.d.)
Ascorbic acid (C₆H₈O₆) is also an effective antioxidant, which helps in slowing down the oxidation
of other chemicals, as well as helping regenerate other antioxidants within the body. (Braun, 2014).
When in neutral or basic solutions, it is shown that Ascorbic acid (C₆H₈O₆) is rapidly oxidised to
Dehydroascorbic acid (C₆H₆O₆) (see Fig 1)
Figure 1: Oxidation of Ascorbic acid
(C₆H₈O₆) to Dehydroscorbic acid
(C₆H₆O₆) (Oregon State University,
(n.d)
In this experiment, the Vitamin C content will be found through the process of redox titration
with potassium iodate (KIO3), in the presence of potassium iodide (KI). Redox titration is defined
, as “method of determining the concentration of a given analyte by causing a redox reaction
between the titrant and the analyte.” (Bijus, 2019)
During the experiment, when Iodate ions (IO3ˉ ) are added to a solution containing iodide ions
(Iˉ ), in the presence of Vitamin C, a redox reaction occurs. (University of Canterbury, n.d.)
Iodine will be formed as Iodide ions are reduced;
IO3ˉ + 6H + 5 e- → ½ I2 + 3 H2O
And iodide ions will be oxidised and will form iodine;
2 I ˉ → I2 + 2e-
When these two half equations are combined, it shows the reactions between iodate and iodide,
which produces iodine.
IO 3ˉ + 5 I ˉ + 6 H+ → 3I2 + 3 H2 O
The iodine produced will then oxidise the Ascorbic acid (C₆H₈O₆) to Dehydroscorbic acid (C₆H₆O₆),
while simultaneously, iodine will be reduced to iodide ions. (University of Canterbury, n.d.)
C₆H₈O₆ + I2 → 2Iˉ + C₆H₆O₆
Once the Ascorbic acid (C₆H₈O₆) in the reaction is all oxidised, the excess iodine will react with the
starch indicator, in turn forming a blue-black colour, highlighting the endpoint of titration.
(University of Canterbury, n.d.)
3:Hypothesis
When exposed to high temperatures, Ascorbic acid (C₆H₈O₆), will undergo oxidation to form
Dehydroascorbic acid (C₆H₆O₆). An increase in temperature will increase the average kinetic energy
of molecules, therefore, the oxidation process of Ascorbic acid (C₆H₈O₆) will take place quicker as
the temperature rises. Not only that, but Ascorbic acid also (C₆H₈O₆) is water-soluble, and will
leach into the water, hence becoming much more degraded as well. Therefore, I predict that as
the temperature increases, the amount of Ascorbic acid (C₆H₈O₆) left in oranges and kiwis
decreases, as shown in figure 2.
Graph predicting the relationship between Temperature( ℃) and Vitamin C content (mg) in oranges and
kiwis
Figure 2: Sketch of predicted
results
Session: May 2021
The effect of temperature on Vitamin C content In Oranges and Kiwis
1: Introduction
Over the past few months, one new activity that I have thoroughly enjoyed doing is cooking.
During my pastime, I would watch videos detailing recipes of dishes, and I would then try cooking
them. More recently, I have been rather intrigued by dishes that contain fruits, as it was
something that I found unique. In particular, two dishes that grabbed my attention were “Orange
chicken pot with rice” and “Baked kiwi tart”, both fruits that are known for containing a high
amount of Vitamin C.
An article that I came across a while ago highlighted the degradation of Vitamin C which was
caused by exposure to heat. This article sparked my curiosity, as the aforementioned dishes with
fruits which I took interest in were required to be cooked at high temperatures. This led me to
question the effect of temperature on Vitamin C content. Inspired by this, when I came across the
chance to investigate the relationship between Vitamin C content and its effect due to increasing
temperatures through the chemistry internal assessment, I opted on the following research
question;
How do increasing temperatures (25.0℃, 40.0℃,55.0℃, 70.0℃, 85.0℃) affect the Vitamin C
content (mg) of oranges and kiwis; determined by redox titration using iodate solution?
2: Background Information
Vitamin C, also known as Ascorbic acid (C₆H₈O₆) is an essential nutrient in the human diet. The
recommended amount of Vitamin C intake for adults is between 60 mg to 95 mg per day. (Snyder,
2019) Vitamin C is extremely significant as it is needed for the growth of body tissues and is used
to prevent and also treat scurvy. Usually, a raw orange contains 0.5mg of Vitamin C per gram,
while a kiwi contains 0.9mg of Vitamin C per gram. (NutritionValue.Org, n.d.)
Ascorbic acid (C₆H₈O₆) is also an effective antioxidant, which helps in slowing down the oxidation
of other chemicals, as well as helping regenerate other antioxidants within the body. (Braun, 2014).
When in neutral or basic solutions, it is shown that Ascorbic acid (C₆H₈O₆) is rapidly oxidised to
Dehydroascorbic acid (C₆H₆O₆) (see Fig 1)
Figure 1: Oxidation of Ascorbic acid
(C₆H₈O₆) to Dehydroscorbic acid
(C₆H₆O₆) (Oregon State University,
(n.d)
In this experiment, the Vitamin C content will be found through the process of redox titration
with potassium iodate (KIO3), in the presence of potassium iodide (KI). Redox titration is defined
, as “method of determining the concentration of a given analyte by causing a redox reaction
between the titrant and the analyte.” (Bijus, 2019)
During the experiment, when Iodate ions (IO3ˉ ) are added to a solution containing iodide ions
(Iˉ ), in the presence of Vitamin C, a redox reaction occurs. (University of Canterbury, n.d.)
Iodine will be formed as Iodide ions are reduced;
IO3ˉ + 6H + 5 e- → ½ I2 + 3 H2O
And iodide ions will be oxidised and will form iodine;
2 I ˉ → I2 + 2e-
When these two half equations are combined, it shows the reactions between iodate and iodide,
which produces iodine.
IO 3ˉ + 5 I ˉ + 6 H+ → 3I2 + 3 H2 O
The iodine produced will then oxidise the Ascorbic acid (C₆H₈O₆) to Dehydroscorbic acid (C₆H₆O₆),
while simultaneously, iodine will be reduced to iodide ions. (University of Canterbury, n.d.)
C₆H₈O₆ + I2 → 2Iˉ + C₆H₆O₆
Once the Ascorbic acid (C₆H₈O₆) in the reaction is all oxidised, the excess iodine will react with the
starch indicator, in turn forming a blue-black colour, highlighting the endpoint of titration.
(University of Canterbury, n.d.)
3:Hypothesis
When exposed to high temperatures, Ascorbic acid (C₆H₈O₆), will undergo oxidation to form
Dehydroascorbic acid (C₆H₆O₆). An increase in temperature will increase the average kinetic energy
of molecules, therefore, the oxidation process of Ascorbic acid (C₆H₈O₆) will take place quicker as
the temperature rises. Not only that, but Ascorbic acid also (C₆H₈O₆) is water-soluble, and will
leach into the water, hence becoming much more degraded as well. Therefore, I predict that as
the temperature increases, the amount of Ascorbic acid (C₆H₈O₆) left in oranges and kiwis
decreases, as shown in figure 2.
Graph predicting the relationship between Temperature( ℃) and Vitamin C content (mg) in oranges and
kiwis
Figure 2: Sketch of predicted
results
