Vitamin C tablets

The technique of hydrodynamic modulation voltammetry (HMV), in which the rate of stirring is pulsed between high and low values, is demonstrated in this experiment. The application of HMV for the quantitative analysis of ascorbic acid in vitamin C tablets using the method of standard additions also is outlined. 

C04-0144. Vitamin C (also called ascorbic acid) is an acid whose formula is HCg H7 Og. When treated with strong base, it undergoes the following reaction HCg H7 0(5 + OH H7 Og + H2 O A pharmacist suspects that the vitamin C tablets received in a recent shipment are not pure. When a single 500.0-mg tablet is dissolved in 200.0 mL of water and titrated with a standard base that is 0.1045 M, it takes 24.45 mL to reach the stoichiometric point. Are the tablets pure If not, what is the mass percentage of impurities (Assume no impurity is either an acid or a base.)... 

Analysis of ascorbic acid (vitamin C) in a vitamin C tablet. 

OO A chemist adds a few drops of deep violet-red iodine solution to a vitamin C tablet. The iodine solution quickly becomes colourless. Then the chemist adds a solution that contains chlorine, CI2. The chemist observes that the violet-red colour of the iodine reappears. Explain the chemist s observations, in terms of redox reactions. 

Consider a manufacturer making vitamin C tablets intended to have a target value of p, milligrams of vitamin C per tablet. Many analyses over a long time tell us the population standard deviation, cr, associated with the manufacturing process. 

This experiment is flexible in that students may choose the samples they wish to analyze. It is suggested that several fruits and vegetables as well as an unknown ascorbic acid sample be available for analysis. The vitamin C content of raw and cooked vegetables can also be measured and compared. Commercially available vitamin C tablets or multivitamin pills provide interesting samples for analysis. The time required for this experiment can be adjusted by controlling the number and type of samples. 

Vitamin C tablets or multivitamin pills Metaphosphoric acid/acetic acid solution, 4%... 

Whole fruits and vegetables-oranges, grapefruit, lemons, limes, green peppers, tomatoes, potatoes, spinach, lettuce, cabbage, and others Vitamin C tablets or multivitamin pills... 

L.16 A vitamin C tablet was analyzed to determine whether it did in fact contain, as the manufacturer claimed, 1.0 g of the vitamin. A tablet was dissolved in water to form a 100.00-mL solution, and a 10.0-mL sample was titrated with iodine (as potassium triiodide). It required 10.1 mL of 0.0521 M I3-(aq) to reach the stoichiometric point in the titration. Given that 1 mol I3 — 1 mol vitamin C in the reaction, is the manufacturer s claim correct The molar mass of vitamin C is 176 g-mol 1. 

Vitamin C cannot be synthesized in the human body and must be obtained from the diet (e.g., citrus fruits, broccoli, turnip greens, sweet peppers, tomatoes) or by taking synthetic vitamin C (e.g., vitamin C tablets, high-C drinks, and other vitamin C-fortified commercial foods). The minimum recommended adult daily requirement of vitamin C to prevent scurvy is 60 mg. Some people, among them the late Linus Pauling, twice Nobel Laureate, suggested that very large daily doses (250 to 10,000 mg) of vitamin C could help prevent the common cold, or at least lessen the symptoms for many individuals. No reliable medical data support this claim. At present, the human quantitative requirement for vitamin C is still controversial and requires further research. 

A typical vitamin C tablet (containing pure ascorbic acid, H2QHe06) weighs 500. mg. One vitamin C tablet is dissolved in enough water to make 200.0 mL of solution. Calculate the pH of this solution. Ascorbic acid is a diprotic acid. 

A coulometric titration method was introduced for sequential determination of sulfite, thiosulfate and ascorbic acid (1) in solutions containing sulfite-thiosulfate or sulfite-ascorbic acid couples. Formaldehyde or acetaldehyde can be used to mask the sulfite component. Two sequential measurements of coulometric time, one for both components in the mixture and one for the sample solution in which sulfite is masked, can be used to determine the concentrations of sutfite-thiosulfate and sulfite-ascorbic acid couples. The method is linear for 0.5-60 p,M 1 in the presence of 0.44-13 (xM sulfite, with RSD 0.1-4% and current efficiency of ca 98.0%. The method can be used for determination of the presence of sulfite and 1 in real sample matrices such as mineral waters and vitamin C tablets . 

Vickery RE. Unusual complication of excessive ingestion of vitamin C tablets. Int Surg 1973 58(6) 422-3. 

Giunta JL. Dental erosion resulting from chewable vitamin C tablets. / Am Dent Assoc 1983 107 253—256. 

Bhagavan HN, Wolkoff BI. Correlation between the disintegration time and the bioavailability of vitamin C tablets. Pharm Res 1993 10 239-242. 

Place a 100-mg vitamin C tablet between two sheets of wax paper and use a rolling pin to grind the tablet into powder. 

The literature contains numerous references to the use of bromine for the estimation of olefinic unsaturation in fats, oils, and petroleum products. A method for the determination of ascorbic acid in vitamin C tablets is given in Section 371-3. 

Determine if a vitamin-C tablet could take the place of these foods. Explain. 

Have you ever tasted sour milk Have you ever exercised so hard that your muscles were tired Ever had an upset stomach after eating too much or been bitten by an ant Cleaned a toilet with toilet-bowl cleaner Taken a vitamin C tablet to prevent a cold ... 

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