• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Aim:To investigate the content of vitamin C (ascorbic acid) content in a commercial tablets and compare this with the manufacturers specification.

Extracts from this document...

Introduction

ANALYSIS OF THE AMOUNT OF VITAMIN C IN A COMMERCIAL TABLETS AIM To investigate the content of vitamin C (ascorbic acid) content in a commercial tablets and compare this with the manufacturer's specification. INTRODUCTION Vitamin C is ascorbic acid which is rapidly and quantitatively oxidized by iodine in acidic medium according to the following equation: The standard method for determining ascorbic acid present in a sample is to titrate a standard iodine solution. But the low solubility of iodine makes this procedure less than ideal. In this experiment, a know excess of iodine is generated in situ by the reaction between an iodine and an iodate and that not reacting with the ascorbic acid is then titrated against standard sodium thiosulphate solution. A standard solution of iodine is unstable and has to be frequently standardised by a standard solution of thiosulphate. Direct titration of tablets against a standard solution of iodine is not recommended. ??? Stoichiometrically in-situ generation of iodine according to the equation (aq) + 5(aq) + 6(aq) ??? 3(aq) + 3O(l) ...........(2) provides a known amount of iodine (which is excess) to oxidize the vitamin C content of tablets . ...read more.

Middle

of moles of I2 left = (0.0969)(7.11000)2 = 3.440 -4 No. of moles of I2 used = 9.112 x 10-4 - 3.440 x 10-4 = 5.672 x 10-4 No. of moles of vitamin C used in the 25cm3 solution= 5.672 x 10-4 Total no. of moles of vitamin C in the 250cm3 solution = 5.672 x 10-3 Mass of Vitamin C = 5.672 x 10-3 x ( 2+12x6+6+16x6 )= 1.021 g Percentage error = (1.021 - 1.0000 ) /1 X 100% = 2.1% DISCUSSION CHOICE OF BACK TITRATION Both direct and back titrations are possible methods. The recommended experiment involves an in-situ generation of excess iodine by reacting a fixed amount of iodate(V) in acidic medium in the presence of excess iodide solution. Unconsumed iodine is determined by back titration against a standard solution of sodium thiosulphate. There is an advantage of using Back titration which is consuming all the unstable reactant at the start of the reaction. In addition, iodine is volatile, Iodine would escape and cause inaccurate concentration of the solution. standard iodine cannot be prepared directly by accurately weighing because iodine is slight soluble in water. ...read more.

Conclusion

As for the exposure to air, 25 cm3 of tablets sample was placed In the conical flask and allowed to expose to air. The amount of ascorbic acid was determined by the same method as mentioned. SOURCE OF ERROR Error in concentration of solutions After standardizing the sodium thiosulphate solution, it might decompose by air and sunlight. As a result, the concentration of the solution would be lower than we expected and the calculated amount of vitamin C would be smaller. In addition,iodide can be oxidized by air (promoted by acids, heat, light).As a consequence, Iodine conctentration increase with time. OTHER CHEMICALS IN THE TABLET MIGHT REACT In this experiment, we have assumed that only vitamin C in the tablet would react with I2. However, we don't actually know whether other chemicals and ingredients inside the tablet would react with iodine solution. If some of the ingredients would react with iodine solution, the calculated amount of vitamin C in the tablet would be greater. CONCLUSION The mass of vitamin C inside the tablet is 1.021g, the tag on the vitamin C tablet claimed that it contain 1.0000 g vitamin C. The percentage error is 2.1 , which is insignificant. So the claim of the tablet maker is justified. ?? ?? ?? ?? CHAN TING HIN 6B11 ? 1 ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Physical Chemistry section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Physical Chemistry essays

  1. Preparation of Standard solution and Standardization of Hydrochloric acid

    Sometimes burettes leak slowly enough to allow titration, but will loose several tenths of milliliter if left for several minutes. Thus, excess volume of HCL(aq) may be added without awareness. As a result, the actual volume of the solution added will be unknown.

  2. Analysis of commercial vitamin C tablets

    Calculate the molarity of Na2S2O3 solution. 4.> A vitamin C tablet is dissolved in 150cm3 of 0.5M H2SO4 5.> The mixture is then transferred into a clean 250cm3 volumetric flask and deionized water is added to reach the graduated mark. 6.> Pipette 25cm3 of vitamin C solution (with dil.

  1. Acid-Base Titrations.

    = 1.48, pH = 14.00 - 1.48 = 12.52 The points calculated so far along this titration curve are shown in the Figure below. The titration curve of an acid with a base will vary not only as the amount of the acid present varies, but also with the strength of the acid, as the Figure below shows.

  2. Analysis of Two Commercial Bleaches

    Then we can find out the amount of iodine in the solution by titration with thiosulphate solution. Thus the amount of iodine in the seaweed can be found. Errors and Improvements: (i) Some of the classmates found that they produced some milky solution after mixing diluted bleach with other chemicals.

  1. Determination of the content of Mg (OH)2 in an indigestion remedy by back titration ...

    * Sodium hydroxide (0.5mol dm-3 ) * Magnesium hydroxide suspension B.P * Distilled water * Methyl orange indicator * Electronic scale Method Illustration showing how to set up equipment for titration, reading the meniscus and a sample results table.2 * The equipment was set up as illustrated * The Magnesium

  2. Drug: Antacid Effectiveness Analysis To determine the neutralizing ability of antacids in different ...

    Taking in too much magnesium hydroxide will initiate serious muscle cramping and lead to diarrhea or constipation. If too much sodium bicarbonate is absorbed by the intestinal tract, blood pH will be changed and this may cause alkalosis in high doses Alkalosis is characterized by headaches, stomach pain, nausea, and vomiting.

  1. OBJECTIVE: To determine the content of iron in iron tablets by titration.

    To calculate the amount of iron left over after titration Iron + sulphuric acid --> iron sulphate + hydrogen gas Fe(s) + H2SO4(aq) --> FeSO4(aq) + H2(g) Concerned with DISCUSSION: CONCLUSION: The percentage of 2-ethanoylhydroxybenzoic acid (acetylsalicylic acid) in aspirin tablets was found to be 51.3%.

  2. Acid-base titration. Objective To determine the concentration of sulphuric acid (H2SO4) using sodium ...

    If we do not use the correct technique, there must have some error in our result. Acknowledgement: T. M. Leung & C. C. Lee, Phy. Chem. I (4th Ed.), p.50-59 "Titration", B Earl & LDR Wilford, Introduction to Advance Chemistry, p.39-43 Discussion: 1.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work