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Comparing Vitamin C content
Principle(s) Investigated: Students will observe the evidence of the chemical reaction between Vitamin C (Ascorbic Acid) and Iodine (I2). This reaction is indicated by the color change of the indicator which will go from dark purple to lighter purple. The lighter results will be due to increasing concentrations of Vitamin C in the samples used. The Vitamin C content will be compared relatively and drinks (samples) will be ranked from highest to lowest content of Vitamin C.
Standards: Chemistry
2a. Students know atoms combine to form molecules by sharing electrons to form covalent or metallic bonds or by exchanging electrons to form ionic bonds.
2b. Students know chemical bonds between atoms and molecules such as H2, CH4, NH3, H2CCH2, N2, Cl2 and many large biological molecules are covalent.
2d. Students know the atoms and molecules in liquids move in a random pattern relative to one another because the intermolecular forces are too weak to hold the atoms or molecules in a solid form.
Investigational and Experimentation
d. Formulate explanations by using logic and evidence.
m. Investigate a science-based societal issue by researching the literature, analyzing data, and communicating the findings. Examples of issues include irradiation of food, cloning of animals by somatic cell nuclear transfer, choice of energy sources, and land and water use decisions in California.
Materials:
Cornstarch
2% Iodine Solution (Can find at local pharmacy)
Water
Heat source
100 mL graduated cylinder
250 mL beaker & 500 mL beaker
Orange juice, Vitamin water, orange flavor Gatorade, Sprite, water (Or any 4 drinks of your choice)
Per group:
5 test tubes (15 mL)
Test tube rack
25 mL graduated cylinder
White paper
Eyedroppers
5 small cups
Procedures:
Since this is a short lab time prepare the indicator right before class. Make the indicator by adding 1 tablespoon of cornstarch to enough water to dissolve into a thin paste. Add 250 mL of water, mix and heat until boiling, continue boiling for 5 minutes. Turn off heat source.
Using the eyedropper add 10 drops of the starch solution to 75 mL of water and mix. Using a clean eyedropper add 1 drop at a time of 2% Iodine until color of starch solution turns dark purple. This is the indicator solution.
Number 5 small cups 1 to 5, 1 for water, 2 for orange juice, 3 for orange Gatorade, 4 Sprite soda, 5 for Vitamin water.
Put 5 mL of indicator solution into each test tube labeled 1 to 5.
Using a clean eyedropper and rinsing the eyedropper between samples, add 10 drops of the samples (drinks) to each test tube. (It is very important to rinse eyedropper between samples to avoid cross contamination). Test tube numbers will correspond to 1 for water, 2 for orange juice, 3 for orange Gatorade, 4 Sprite soda, 5 for Vitamin water.
Observe and record the changes taking place.
Hold each test tube against the white sheet of paper and arrange from lightest to darkest purple. The lighter solutions have a higher Vitamin C content.
Rank the drinks based on results of Vitamin C content, from highest to lowest.
Lead students into discussion about the reaction taking place and what was observed. Did all drinks cause a change in color?
Discuss role of Chemistry as applied in this case to Nutritional evaluation.
Student Prior Knowledge:
Chemical Reaction: Students should know that a chemical reaction is a chemical change in the substance. In a chemical reaction the atoms of one or more substances are rearranged to form different substances.
Evidence of a chemical reaction: Students should know that there is evidence that tells us that a chemical reaction has taken place. Evidence can be observed in temperature changes, change in color, odor, gas bubbles and appearance of a solid (precipitate).
Lab procedure: Students should know how to carry out a basic experiment by following the lab procedure (protocol) along with making and recording observations.
Use of knowledge: Students should be able to use observations to draw a conclusion.
Explanation:
This experiment allows the students to observe evidence of a chemical reaction. The evidence of the chemical reaction taking place will be observed in the change of color of the solutions. To compare the Vitamin C content of selected drinks we will use an indicator containing starch and Iodine. The Vitamin C (Ascorbic acid) reacts with the Iodine (I2). In the reaction two H+ and two electrons are split off from Ascorbic acid to form Dehydroascorbic acid, Iodine (I2) is reduced to I-.
C6H8O6 + I2 à C6H8O6 + 2I- + 2 H+
Ascorbic Acid + Iodine à Dehydroascorbic Acid + 2I- + 2H+
(Vitamin C)
*Thisis an oxidation- Reduction reaction. Vitamin C is being oxidized and Iodine is being reduced.
The I2 prefers to react with the Ascorbic acid (Vitamin C). When the Ascorbic acid (Vitamin C) is used up in the reaction, the remaining I2 will react with the starch showing a purple color. Comparison of the samples will enable students to classify the samples from lightest to darkest purple and extrapolate that the lighter samples were produced by samples that contained more Vitamin (Ascorbic acid). Since the indicator contained equal amounts of Iodine, the different concentrations of Vitamin C in the samples left varying amounts of Iodine after the reaction. The left over Iodine is then available to react with the starch producing different shades of purple.
Questions / Answers:
Q: As you add the sample of the drink to the indicator (purple solution) what causes the change in color (or no change in color).
Answer: Each sample of the drinks selected contains different amounts of Vitamin C. The color change is produced when Vitamin C reacts with Iodine.
Q: Humans cannot make their own Vitamin C. We must get our Vitamin C from what we eat and drink, as part of our diet. What is a condition caused by Vitamin C deficiency?
Answer: Scurvy is caused by Vitamin C deficiency. Symptoms of scurvy are loss of appetite, bleeding gums, loose teeth, and swollen ankles and bleeding spots in the skin. There are other conditions which can result from Vitamin C deficiency since Vitamin C is a catalyst in many biological reactions.
Q: What will happen to a person who only drinks Gatorade, soda and has a diet very low in fruits and vegetables?
Answer: We have found out that Gatorade and soda do not contain significant amounts of Vitamin C, they may not contain any. Other sources of Vitamin C are fruits and vegetables so a person that does not have them as part of their diet would suffer from Vitamin C deficiency.
Applications to Everyday Life:
Nutrition: It is important to be informed of the content of what we consume, eat and drink. As our busy lives move us towards more prepared foods we have to be able to supplement with Vitamins or complement with foods that contain the essential Vitamins and minerals for a healthy body. We have to be careful not to replace nutritional drinks like orange juice for popular drinks that do not contain significant amounts of needed vitamins.
Agriculture: Most people would be shocked to find out that not all fruits and vegetables have the amounts of Vitamins and minerals they are supposed to have. The depleting farming lands are producing crops of low quality. This affects largely the low socio-economic populations that have limited resources. This is just one more issue to add to the nutritional deficiencies already present in these populations. Evaluation of nutritional content is essential to keep growers accountable.
Advertisement: Students should be aware of false advertisement and visually misleading labels. Many people would assume that Sprite which the label says it contains natural flavors or any other soda showing an orange or lemon on the label would contain a good amount of Vitamin C. In fact we have observed that the Sprite soda did not contain a measurable amount of Vitamin C. The observation and deduction techniques learned in a lab can be applied to our daily life and makes us informed consumers. It is crucial to read nutritional labels.
References:
www.sciencemadesimple.com/nutrition_projects
www.math.unl.edu/foodscienceworkshop.pdf
www.lpi.oregonstate.edu/infocenter/vitaminc
www.researchnestle.com/science
Worksheet on following pages below and also as an attachment at end.
Name: Period:
LAB WORKSHEET – Comparing the Content of Vitamin C
Samples: 1) Water 2) Orange Juice 3) Orange Gatorade 4) Sprite soda 5) Vitamin water
From the samples provided, which drink do you think has the most Vitamin C? ___________________
Which drink do you think has the least? _____________________
We are going to measure the relative Vitamin C content using a starch / Iodine indicator.
*Note: An indicator is a substance that shows the presence, absence, or concentration of another substance by means of a characteristic change, especially a change in color. Another example of an indicator if pH paper.
What is happening in this chemical reaction?
C6H8O6 + I2 à C6H6O6 + 2I- + 2H+
Ascorbic Acid (Vitamin C) + Iodine à Dehydroascorbic Acid + 2I- + 2H+
This is an oxidation-Reduction reaction, Vitamin C is getting oxidized and Iodine is getting reduced.
Note: Iodine prefers to react with Vitamin C. The samples with higher content of Vitamin C use up more of the iodine. Once all the Vitamin C is used up in the reaction, the left over Iodine then reacts with the starch to produce the different shades of purple.
Mini Lab:
Step 1) Put 5 mL of indicator solution into each test tube (Be careful Iodine solution can stain)
Step 2) IMPORTANT: Rinse eyedropper between samples
Add 10 drops of the sample to the corresponding test tubes numbered 1 – 5
Step 3) Observe and record any changes
Step 4) Hold each test tube against a piece of white paper and arrange test tubes from lightest to darkest.
Step 5) Rank the drinks in order of higher Vitamin C content to lower Vitamin C content based on the table above.
Initially you predicted which drink would have more Vitamin C. Does your choice match the results obtained from your observation and result table above? _____________________________
The label on Sprite show a lemon/lime and the label on Gatorade say it is orange. Would this lead you to believe that there is lemon/orange juice (Vitamin C) in these drinks? _________________________________
What do the results from this experiment show about their Vitamin C content?
Sprite’s Vitamin C content ______________________
Gatorade’s Vitamin C content ____________________
What have we learned about product names and labels? ________________________________
How can we use this information in our everyday life? ______________
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