This was my internal assessment piece for Chemistry HL in which I scored 5 and had a predicted 6. It has a good structure and is simple to follow. Very good to use as reference when starting IA planning.
Comparing ascorbic acid content between freshly pressed juices and industrial
juices —Chemistry Internal Assessment
Introduction
This Internal Assessment provides insight and analysis into the Vitamin C content of several
fruit juices. Fruits and vegetables have been known to be great sources of Vitamin C. For a year
now, I have been involved in the production and selling of freshly pressed juices at a stand to
collect funding for various causes. Most customers where inclined to purchasing the juices due
to their homemade and natural nature which led me to wonder the reason behind this and if
natural juices had healthier characteristics in terms of Vitamin C content. This sparked my
curiosity and thus, gave me the opportunity to investigate this, using the following research
question:
How does the Ascorbic Acid content vary in industrial and natural juices according to the
different juice types (Guava, Lemon, Orange and Pineapple)?
Background information
Vitamin C, also known as Ascorbic Acid or L-ascorbic acid, is a water-
soluble organic compound with antioxidant properties. It is involved in
several metabolic processes of animals. Whilst most animals can
synthesis Vitamin C, humans and other vertebrates lack an enzyme
that is essential for ascorbic acid’s biosynthesis from D-glucose.
Because of this, Vitamin C must be a component of our daily diet.
Vitamin C —ascorbic acid
Vitamin C is a prime component in the synthesis of collagen. It is also a physiological
antioxidant that limits the damage caused by free radicals (unstable molecules that can
damage cells). Research has also show its importance for the immune system, whether it be by
helping fight bacteria or by its anti-carcinogenic activity.
Due to its important presence in one’s diet, an accurate amount of ascorbic acid is required.
Too much Vitamin C in one’s diet can cause stomach pain, flatulence and diarrhoea. On the
other hand, Vitamin C deficiency can cause scurvy, a disease characterised by swollen
bleeding gums, haemorrhaging, weak blood vessels and in some cases even death.
Vitamin C can be determined using a redox titration. Iodine is insoluble yet when complexed
with triiodide, aqueous iodine is generated.
I 2 + I - ↔ I 3-
Said iodine can then be used to oxidize Vitamin C and form dehydroascorbic acid.
C6H8O6 + I3-+ H2O → C6H6O6 + 3I- + 2H+
1
, During the reaction, the aqueous iodine will build up and react with the iodide ions, they will
then react with the present starch and hence for a blue-black complex, indicating the endpoint
of the titration.
It is worth noting this titration can also be done using just the iodine solution however the
iodate will give more accurate results due to its stability.
Aim
The aim of this experiment is to test the vitamin C content in juice samples using a redox
titration. Given the fact that fruits contain other acids apart from ascorbic acid, a redox titration
will be better than an acid-base titration (an alternate method to measure the Vitamin C
content), like this, the other acids will not interfere with the oxidation process occurring.
However, it is worth noticing that for the sole purpose of this experiment the assumption that
there were no other interfering oxidative processes presents was made.
Prediction
Industrial juices and products in general are usually chemically enhanced to meet certain
requirements. In addition, natural juices do not possess preservatives and other chemicals
capable of maintaining the Vitamin C content. Because of this, I expect the industrial juices
overall to have a higher Vitamin C content that the natural ones.
Methodology
Substances: Materials:
• 100-ml Iodine solution (0.5%) • Safety goggles
• 420-ml Distilled water • Lab coat
• 250-ml Starch solution (1%) • Graduated cylinder (25-ml)
• 20-ml Vitamin C standard solution (0,25g/100ml) • 2 graduated pipettes (3-ml)
• 20-ml Orange juice (freshly pressed) • 2 conical flasks (200-ml)
• 20-ml Pineapple juice (freshly pressed) • 2 beakers (100-ml)
• 20-ml Lemon juice (freshly pressed) • Funnel
• 20-ml Guava juice (freshly pressed) • Stand and burette clamp
• 20-ml Orange juice “La Estancia” • White tile
• 20-ml Pineapple juice “La Estancia” • Burette (50-ml)
• 20-ml Guava juice “La Estancia” • Pestle and mortar
• 20-ml Lemon juice “La Estancia”
Variables:
Independent variable Samples used Variation method
Type of fruit juice Industrial and freshly Natural juices were made respectively
made guava, pineapple, and industrial ones purchased. They
orange and lemon juice were all kept in the same conditions
afterwards.
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