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Lab G: The Volume Analysis of Vitamin C

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Tamara Freeman, 98006923

TA: Avogadro Numerol

Lab Performed: Nov. 2, 2020

CHEM 1X1, L99

Lab Submitted: Nov. 16, 2020


Vitamin C which is also known as ascorbic acid is an essential nutrient which can be derived from some foods. It is soluble in water and helps ensure that the immune system work properly to protect the body from diseases. It also protects cells from free radicals which are compounds produced when the body metabolize food for energy or when the body is exposed to some degenerative conditions in the environment such as pollution in the air, smoking cigarette and even ultraviolet rays of the sun. Furthermore, vitamin C is also required in order to produce collagen that helps in healing wounds and enhances iron absorption from plant-based food (NIH, 2019).

Just like all other nutrients, the body just needs a certain daily amount of vitamin C which depends on age. Below is a table showing the recommended amount of ascorbic acid for every life stage according to the National Institutes of Health (2019).

Life Stage Recommended Daily Amount in mg
0-6 months 40
7-12 months 50
1-3 years 15
4-8 years 25
9-13 years 45
14-18 years (boys) 75
14-18 years (girls) 65
Adult men 90
Adult women 75
Pregnant teens 80
Pregnant women 85
Breastfeeding teens 115
Breastfeeding women 120

The NIH (2019) also recommends adding an additional 35 mg to the values found in the table for people whose lifestyle involve smoking. When most people can get enough vitamin C through intake of food or drinks, some people may have difficulty getting enough of this nutrient such as people who smoke, people who do not have access to a variety of food, and people who have certain medical conditions like kidney diseases. Not taking in enough or deficiency in ascorbic acid for an extended period of time may lead to a disease called scurvy which causes inflamed gums, fatigue, small red or purple spots on the skin, pain in the joints, poor wound healing, and corkscrew hairs including additional symptoms such as depression, loss of teeth, and swollen, bleeding gums which can cause death if not treated. Food such as citrus fruits, other fruits and vegetables, and food or drinks fortified with vitamin C are some examples of the sources of vitamin C for the body. On the other hand, too much vitamin C may cause stomach cramps, diarrhea, and nausea. The established maximum amount of vitamin C intake is shown in the table below (NIH, 2019).

Life Stage Upper Limit of Daily Vitamin C Intake in mg
0-12 months Not established
1-3 years 400
4-8 years 650
9-13 years 1200
14-18 years 1800
Adults 2000

The data above shows that induvial must only take vitamin C within a range in order to maintain proper health. Just like many others, the amount of ascorbic acid in the body must not be too low or too high. This leads to the understanding that a person should only take dietary supplements if his vitamin C intake is low. Most supplements do not come in pure amount which means that a 500 mg tablet does not necessarily mean 500 mg of vitamin C. This experiment aims to discover how much vitamin C is in a single tablet which can give people ideas on how much of the nutrient are they are adding into their body. This is achieved using titrimetric methods and knowledge of stoichiometry by calculating the amount of vitamin C that reacts with iodine. The principle is based on the known stoichiometric reaction:

in which the unknown amount of vitamin C reactant is allowed to react with a known concentration (and amount) of iodine (I2) in a 1:1 ratio producing an endpoint indicated by the changing of the color of the solution into blueish-gray. Therefore, the amount of I2 in moles used is numerically equal to the amount of ascorbic acid present in the solution. Since I2 is in excess, to measure the amount of ascorbic acid more accurately, a back-titration is needed to determine the excess amount of iodine.


The procedure for the experiment was done in two parts as followed:

Part A involved the preparation of the analyte in which an ascorbic acid tablet is was dissolved in 100 mL of distilled water in a clean 250 mL beaker which was also continuously stirred using a stir plate and magnetic stir bar for 10 minutes. To ensure that most vitamin C was dissolved, a glass stir rod was used to gently help break up the tablet followed by 5 more minutes of stirring. The resulting solution was then transferred into a 500 mL volumetric flask through a gravity filtration set up and was mixed thoroughly afterwards by inverting the flask at least 10 times. The unneeded apparatus was returned and the analyte was set aside to prepare the titrant in part B.

Part B involves the preparation of the titrants for the main and back titration as well as the actual titration itself and observing the reaction in the conduct of the experiment. Here, a burette was rinsed and filled with the sodium thiosulphate solution provided by the teaching assistant. For the main reaction, 25 mL of dilute standard KIO3 solution was pipetted into a 125 mL Erlenmeyer flask in which 0.2g of KI was added as well as 1 mL of 1M sulfuric acid. Afterwards, 10.00 mL of the vitamin C solution was added, mixed and allowed to react with the iodine. The initial burette reading was recorded to 2 decimal places and the contents of the Erlenmeyer flask was titrated slowly with stirring until a pale-yellow color was obtained. Afterwards 20 drops of starch solution were added and the titration was continued until the blue color just disappeared and the final burette reading was recorded. The titration was repeated twice in order to obtain consistent results and the titration volumes were averaged.

After the experiment, the unused KIO3 and Na2S2O3 were disposed in the inorganic waste containers while all other solutions were poured down the drain.


The data calculations are on the excel file and here are the photos of the handwritten calculations. Units not shown in excel are shown in the handwritten calculations. The uncertainties are not reflected on the handwritten notes but are shown and calculated in the excel file.

From the data calculations above, the amount of vitamin C calculated from the experiment is greater than what is listed as the amount of vitamin C per tablet. The percent error is $% error = frac{1002 mg – 500 mg}{500 mg} x 100% = 100.4%$ or slightly more than twice the theoretical amount.

Discussion and Conclusion:

The amount of vitamin C calculated in the experiment is more than what is written in the amount of vitamin C listed in the tablet with a percent error of 100.4%. Possible explanations for this error are: (1) the chemical reactions do not go into completion, (2) the amount of iodine reacted with the sodium thiosulfate is smaller than the theoretical amount resulting to a larger difference in the moles of I2 from KIO3 solution minus the moles of I2 used by sodium thiosulfate thus the amount of moles of vitamin C calculated is much larger than it is supposed to be, (3) the analyte from which the 10 mL aliquot was taken from was not homogenous such that the aliquot contained more vitamin C and when the dilution factor was multiplied to the final amount of vitamin C to determine its amount in moles in the original solution became larger. Despite this, the experiment showed that it is possible to determine the amount of vitamin C contained in the tablet and recheck if it corresponds to the amount listed in the packaging. Furthermore, this experiment showed that in volumetric analysis of a sample, care must be observed especially in reading values for volume in the titration. It is also essential that when titrating, one must be very vigilant to at what point the endpoint is seen in order to stop adding additional titrant. Moreover, if an excess amount of titrant does go into the analyte, it is still possible to account for this amount by using back titration.

In summary, the importance of taking the proper amount of vitamin C is essential for a healthy lifestyle. In this experiment, the amount of vitamin C in the tablet was determined to be 1002 mg which is greater than the amount listed in the tablet. The determination of this amount can be done by volumetric analysis in which the amount of vitamin C is in a 1:1 ratio with the amount of iodine. The iodine can be provided by reaction KIO3, KI, and H2SO4. The reaction of iodine with vitamin C results to the solution turning dark blue. Lastly, the excess amount of iodine can be determined through the back-titration reaction with sodium thiosulfate whose endpoint is signaled the color change of the dark solution into a clear solution. This experiment can be used to double check the amount of vitamin C in the supplement tablets that consumers are using in order to prevent providing more of the nutrient than the normal recommended daily intake and thus minimizing the risk for overdosage. The data from this experiment can also be used to monitor the amount of vitamin C taken into the body especially for individuals that do not reach the recommended daily amount of vitamin C.


Ods.od.nih.gov. 2020. Office of Dietary Supplements – Vitamin C. [online] Available at: <https://ods.od.nih.gov/factsheets/VitaminC-Consumer/> [Accessed 18 November 2020].

(I read from the instructions references in your papers follow a specified format under section 6.8 Citation Styles so please feel free to revise this citation if needed. Afterwards, please remove this comment.)

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