Determining Vitamin C Concentration Lab
Spring 2006
Introduction
Vitamins are organic compounds that must be present in small amounts in order for
normal metabolic processes to occur. They cannot be synthesized by the body in adequate
amounts, so these required nutrients must be obtained through food or, more recently,
supplements such as vitamin tablets.
Vitamin C (ascorbic acid, VC) is a water soluble vitamin which is unstable and can be
destroyed by oxidation, heat, light and alkalis. Its functions are not all fully understood,
although it is known to be necessary for the production of collagen, essential for healthy
teeth and gums, and vital for such connective tissues as bone, cartilage, and the fibrous
connective tissue of skin. It also promotes the absorption of iron and aids in resistance to
infection.
There is debate over how much VC is needed, but 10 mg per day is enough to prevent
deficiency symptoms such as scurvy, tooth decay, soft and bleeding gums, swollen or
painful joints, slow healing wounds, bruising and nosebleeds. The Recommended Daily
Allowance, or RDA, for the average adult is 60 mg per day. The body will excrete or
oxidize excess VC, although too much may cause nausea, stomach cramps and diarrhea.
VC is naturally found in many plants, with the highest concentrations being found in
citrus fruits, citrus juices, broccoli, tomatoes, and cabbage. It is also found in other green
leafy vegetables and fresh fruits but in lesser amounts.
Method
This laboratory experiment uses a color indicator to indirectly measure the VC
concentration in a solution. Normally iodine reacts with starch solution and turns it into a
blue/black color. Ascorbic acid (VC) is a very strong reducing agent and will bleach the
color from the iodine added to the solution. When the ascorbic acid is used up, the added
iodine solution will then react with the starch in the solution, turning the solution
blue/black.
With a control sample of known VC concentration, you can calculate VC concentrations
of unknown samples.
Materials
On each bench, each group will find:
2 5 ml syringes
1 1 ml transfer pipette
4 stirring rods
6 50 ml disposable beakers, labeled and pre-poured:
10 ml starch solution
20 ml iodine solution
25 ml control VC solution
25 ml sample 1
25 ml sample 2
25 ml sample 3
paper towels, beach covers etc.
You need to put on a bench apron or a lab coat when you walk into the lab.
Procedures
A. Determine the Baseline:
1. Using transfer pipette, add 1 ml of starch solution to the control VC solution
2. Stir with a stirring rod till mix
3. Draw 5 ml iodine solution into the syringe
4. Slowly add the iodine solution to the control beaker, drop by drop, stirring the
liquid between each drop, taking care not allow the tip of the syringe touching the liquid
in the beaker or spill the liquid from the beaker. Continue adding and counting the drops
until the liquid in the beaker turns blue/black. This process is called “Titration”.
5. Record in your data sheet, the amount of iodine left in your syringe and the number
of iodine drops used in the titration.
6. Push the remaining iodine back into the iodine beaker. Now you complete the
baseline measurement.
B. Determine Unknown Samples:
Repeat step 1-6 for sample 1, then sample 2, then sample 3. Use fresh stirring rod for
each sample.
(Suggestion for the group, everyone would watch and help one member to perform the
baseline measurement, then take turns to measure samples 1-3, in sequence or
simultaneously. Report to the group and complete the data sheet).
Data Analysis
A. The Concept of Concentration:

Concentration of a Material in a solution is defined as the Weight of the material
(e.g., in kilogram, gram, milligram) per Volume of the solution (in liter, deciliter,
milliliter). It is expressed as
Concentration = Weight/Volume
[Material] in unit of mg/ml, g/dl, kg/l
B. Determine Sample Vitamin C concentration [VC]s based on VC concentration of the
Control [VC]c:

Ratio Formula to Determine Concentration:
[VC]c_________
# Titration Drops
for Control
=
[VC]s_________
# Titration Drops
for Sample
 Your control solution contains 1 mg/ml of Vitamin C, therefore
Vitamin C concentration of your sample, [VC]s (in mg/ml)
=
1
# TD for Control
x
# TD for Sample
=
C. Translating Lab Data to Daily VC Intake:

Recommended Daily Allowance of VC is 60 mg per day, calculate the volume of
the sample you need to drink to meet the RDA of 60 mg using the formula:
Volume = Weight/Concentration
Volume (ml) =
60 mg
[VC]s mg/ml
=
 Translate that volume into food serves, e.g., cups or fluid ounces:
(1 ml = 0.034 fl.oz = 0.004 cup)

Calculate the volume of juice you need to drink to meet RDA of Vitamin C for
other samples: (hint, you need first to calculate their [VC].