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- CHEM1009 (CHEMISTRY)
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CHEM 1009Percent Content
Required Readings
1. Please read pp. 180 - 181 from the textbook.
2. Please complete the attached pre-lab quiz and ask your instructor to sign it before the
lab starts.
Required Items
Lab coat, safety goggles, shoes (no open toes, flip-flops or sleepers), one laptop or tablet,
textbook, laminated periodic table, calculator, pencil and eraser.
Purpose
In this experiment students will:
1) Demonstrate the principle of percent content in relation to the amount of vitamin C
present in non-prescription vitamin tablets.
2) Determine the concentrations of vitamin C in reference and test solutions.
3) Compare the results obtained with the theoretical (expected) values to obtain the
percent yield of the test conducted.
4) Research the recommended daily amount of vitamin C for adults and compare it to
the amounts from the analysis of the experiment.
Introduction
Vitamin C is a water-soluble vitamin that is that is needed daily to maintain skin and teeth,
to resist stress and infection, and of course, to prevent scurvy. The vitamin is present in
foods such as citrus fruit, green vegetables, and potatoes. It is relatively heat resistant, but
it is easily deactivated by enzymes during cooking or by oxygen when food is stored in the
presence of air. The chemical instability of vitamin C is due to the fact that it is a strong
antioxidant or reducing agent and can be deactivated by a wide range of oxidizing agents.
For example, the oxidation of vitamin C by atmospheric oxygen in opened citrus juices
slowly reduces the vitamin C concentration in these juices. As well, metals like copper and
iron increase the rate at which the vitamin is destroyed.
This experiment studies different brands of vitamin C tablets as sources of vitamin C and
compares the results with the amount of vitamin C listed on the labels.
Chemically, vitamin C is both a reducing agent and a weak acid. The vitamin C
concentration in the solutions made from daily dose tablets of vitamin C will be determined
using an oxidation / reduction titration in which one solution will be added to a second
solution in order to determine the concentration of vitamin C (H 2C6H6O6).
The titration reaction is: H2C6H6O6 + I3- + H2O à C6H6O6 + 3 I- + 2 H+
In this experiment, the concentration of the iodine solution will be confirmed by reacting it
with a reference solution containing a known amount of ascorbic acid (vitamin C) in the
presence of starch (an indicator). The yellow iodine solution will react with the ascorbic
acid to form colorless iodide ions. Once all the ascorbic acid is consumed, then the excess
iodine will react with the starch to form a dark blue color in the solution (end point of the
reaction).
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CHEM1009: Percent Content
, Once the concentration of the iodine is confirmed, the same iodine solution will be used to
react with a solution containing a vitamin C supplement. The value of the iodine
concentration obtained in the first (calibration) step will be used to calculate the
concentration of vitamin C in the sample. This process will be repeated for at least two
different source of vitamin C.
The final calculations in the experiment will be necessary to convert the concentration of
vitamin C to the mass amount in the original supplement. Then the amount determined
experimentally can be compared to the value shown on the label of the container (per
serving or per tablet).
The recommended daily amount (RDA) of vitamin C will be compared to the value obtained
for each source of vitamin C and expressed as a percentage of the RDA. Furthermore,
using the weight of an original tablet/packet, the % mass/mass of the vitamin C in the
tablet will be calculate.
The video links below shows two practical versions of this lab experiment.
https://www.youtube.com/watch?feature=player_detailpage&v=p8xt6_gd664#t=0
https://www.youtube.com/watch?
v=1P3W9DykGBg&list=PLLnAFJxOjzZvsrmLQTnLgEi2Wc5t-
Tb6J&feature=player_detailpage#t=0
Safety
o Wear your lab-coat and goggles before entering the laboratory.
o The use of splash goggles is mandatory; all solutions used in this experiment may damage
the eyes.
o SHOES must completely cover the feet (no sandals, shoes with holes, sleepers etc.).
o Long hair should be tied back.
o Students will use glassware which may break on impact or if dropped. Glass fragments may
cause injuries (cuts) to hands, feet or legs. If injured seek emergency first aid assistance
immediately; notify the instructor.
o Dispose of any broken glassware in the broken glass container.
o The iodine solution is toxic if ingested and may be irritate the skin. It may leave stains on
clothes or skin; a small amount of the vitamin C solution may be used to remove the stains.
o If a solution gets into a person’s eyes, flush the eyes with water at the eyewash station
for 15 minutes and have someone notify the instructor.
o If a solution spills on a surface, wipe it up with paper towels and rinse with water, being careful
not to touch the liquid.
o If a solution is spilt on a person, immediately rinse the area with lots of water and have
someone notify the instructor.
o Instructors should ensure that all reported spills are cleaned up before student activities
resume.
o Refer to the chemical Safety Data Sheets for additional information and the Standard Operating
Procedures (SOPs) for safe use of equipment.
o At the end of the lab, just before leaving, wash hands thoroughly with soap and water.
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CHEM1009: Percent Content
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