Personal iodine is free to reaction with the starch

Personal Engagement:

            L-ascorbic acid, commonly referred to as Vitamin C is a type of mineral which is present in various foods. Unlike other organisms, humans are unable to synthesize vitamin C, which is why it’s crucial to receive this vitamin from other dietary products1. This mineral is crucial for the regeneration of essential antioxidants including alpha-tocopherol (vitamin E). Oranges are stereotypically viewed as fruits containing a large amount of vitamin C. Today, many people lean towards organic products as they are often viewed as healthier, more ethical and better in taste in regards to those grown with pesticides

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            Anemia is a condition where blood lacks hemoglobin, or enough red blood cells2.It can be caused by lack of minerals and vitamins including vitamin deficiency. As someone who suffers with anemia, it’s essential I maintain my vitamin levels. If not, my immune system will continue to deteriorate, increasing my vulnerability to severe infections3.  I am SS1 interested in SS2 this question because Organic foods are always viewed as healthier. However, certain consequences such as price play a factor. The purpose of this lab is to understand whether or not purchasing organic oranges for the sole purpose of gaining more vitamin C is worth it.

Research Question:

Do organic oranges have higher Vitamin C content than conventional oranges?

Background Information:

            Vitamin C concentration will be investigated by a redox titration concerning potassium iodate reacting with potassium iodide. When iodate ions,  are added to an acidic solution containing iodide ions  an oxidation-reduction reaction would occur:

Firstly, the iodate ions are reduced to form iodine,

In the meanwhile, iodine ions are further being oxidised to form iodine,

When these 2 equations are combined, it forms a reaction between iodate and iodide

Iodine which is formed by this equation would oxidise the ascorbic acid, or vitamin C present in the oranges. Once all the ascorbic acid is oxidized, excess iodine is free to reaction with the starch indicator4.


I think organic oranges have higher vitamin c concentration because they are “organically” grown without the needs of preservatives, pesticides and fertilizers. This preserves essential nutrients in the fruit, including the vitamin C concentration.


This experiment will consist of 5 trials for both organic and non-organic oranges. I have decided to pick 5 trials because it’s the ideal number of trials used in most science labs. With several trials, it gives scientists more data points which helps to illustrate a more reliable answer. Furthermore, data points after 5 are considered irrelevant. Also if I conducted more trials it would be a waste of essential resources and there is also a constraint of time.

To maintain the authenticity of this experiment, I have made the following items constants, independent and dependent variable. These contents are described further below:

Table 1: Independent, Dependent and Control Variables

Independent Variable

Dependent Variable


Source of Vitamin C
For this experiment, the source of Vitamin C will be derived from organic and conventional Navel Oranges

Amount of Vitamin C
As source of orange changes, it will inevitably impact the amount of Vitamin C contents, measured in grams

Concentration of BaseSS3 
Solutions such as  have the same concentration throughout the experiment to avoid a difference in pH levels when titrating the oranges
Amount of Each Substance Used
Amount of solution used, will always remain the same.
Type of Orange
Navel oranges are being used for this lab experiment


It’s important to ensure we control some elements of the experiment. This will ensure the lab is as authentic as possible. Table 1 lists some control variables used in the lab. Now a list of why it’s important to maintain these control variables will be explained in detail.





Table 2: Control Variables

Control Variable


Concentration of Base

Inflections in the amount of concentration used during the lab can either cause the orange to either be very titration or it may not be basic enough to withhold the acidity of the orange solution. Keeping the concentration of the base a constant will ensure only the amount of Vitamin C in the specific orange is being measured.  

Amount of Each Substance Used

Once again, the question recalls for deriving the amount of Vitamin C concentration between organic and conventional oranges. If the amount of solutions being used are altered throughout the experiment, it can impact the overarching question which we are trying to solve.

Type of OrangeSS4 

It’s crucial to keep the species of the orange the same because the mineral levels fluctuate depending on the type of oranges as well. Keeping this a constant will ensure the results are being collected from the same type of orange to avoid any discrepancies.



          The following materials, including equipment and solutions will be needed to follow the procedure of the lab experiment.


6 Beakers
Erlenmeyer Flask
Orange Juicer
Strainer (Optional)

Mortar & Pestle
Retort Stand
1 Pipette
2 Eye Droppers



Orange Juice Solution: 5mL of Juice, 10mL of HCL, 10 drops of 3% starch, 10 drops of  and 50 mL of distilled

NOTE: Organic Juice Solution is made in the same manner for both organic and conventional oranges.


 Solution: 12.5mL of  mixed with 37.5mL of distilled

Starch Indicator Solution: 1.5g of starch mixed with 50mL of distilled


100 mL HCL
25 mL of Organic Navel Orange Juice
25 mL of Conventional Navel Orange Juice

15g of Starch SS6 
1000mL of distilled


1.     Create all solutions found in the “solutions” sections and place each solution in one beaker.

2.     20mL of the Orange Juice solution is placed into a 250mL Erlenmeyer flask and placed under the burette (refer to image 1)5

3.      solution is placed in the burette

4.     Titrate the sample, until there is a permanent trace of a dark blue-black colour (refer to image 2)6

5.     Repeat the titration, alternating between organic and conventional oranges.

Safety Precautions:

During the experiment, certain safety precautions must be respected and followed. Some of them are listed below and must be considered to protect the health of yours and others7:

1.     Eating and Drinking is not permissible

2.     Safety equipment, including goggles and gloves must be worn at all times

3.     Loose Clothing must be tucked in

4.     Long hair must be tied up

5.     Have a neat lab space at all times

6.     Clean up work area after the lab is completed

7.     Wash hands after the experiment is conducted

8.     Ensure pouring substances on eye level to avoid any possible spills of hazardous materials

9.     All waste must be disposed in the “environmental waste” bin in the local area. (Refer to image 1)

Environmental Concerns:

A large aspect of this lab is deriving Vitamin C concentration from conventional oranges. Typically, these types of fruits are grown with pesticides and added minerals. Pesticides used in these products can contaminate soil, water and other vegetation. Not only can they kill insects or weeds, they are also toxic to other organisms including fish, beneficial insects and plants8. Leaning towards foods which are organic are important not only for our health, yet the wellbeing of the environment.

Ethical Concerns:

There are no ethical concerns pertaining to this lab experiment.  

Additional Notes9:

          Iodine can stain both skin and clothing. If staining does occur, alcohol can remove skin stains, while cleaning solutions are available for clothing.














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