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

Analysis Of Commercial Vitamin C Tablets

Extracts from this document...

Introduction

Experiment 5 Date: 18-10-2005 Analysis Of Commercial Vitamin C Tablets Objective To determine the mass of Vitamin C in 1 pill of Vitamin C tablet. Introduction In this experiment, the concentration of sodium thiosulphate solution is not given. So, we need to standardize it through titration. Sodium thiosulphate reacts with iodine in the following reaction: I2 + 2S2O32- ----------------->2I- + S4O62- After an amount of S2O32- is added, the solution of I2 turns pale yellow. When starch solution is added and more S2O32- is added, the solution reaches its end point, which is colorless. In this way, the molarity of the thiosulphate solution is determined. Vitamin C could be oxidized by iodine in the presence of acid in the following equation: Due to the low solubility of iodine, direct titration of iodine solution and Vitamin C is unsuitable. Then how could the experiment be done? The experiment could be done by adding acidified Vitamin C solution into potassium iodide solution. Then, we add potassium iodate to allow the following reaction to take place: IO3- + 5I- + 6H+ ----------------> 3I2 + 3H2O I2 formed in this reaction could react with the Vitamin C in as mentioned in the above equation. ...read more.

Middle

of moles of KIO3 used in each titration= (0.682/214.1)/10 = 3.185 X 10-4 moles. No. of moles of Na2S2O3 used in each titration = 3.185 X 10-4 X 6 =1.91 X10-3 moles. Molarity of Na2S2O3 = 1.91 X 10-3 / 38.067 X 1000 =0.0502M Trial First Second Final burette reading/cm3 16.3 32.0 16.9 Initial burette reading/cm3 0.7 16.3 1.3 Volume of Na2S2O3/cm3 15.6 15.7 15.6 Table showing the data obtained when titrating the Vitamin C solution Mean titre = 15.633cm3 No. of moles of Na2S2O3 used = 15.633/1000 X 0.0502 = 7.849 X 10-4 moles No. of moles of I2 reacted with Na2S2O3 = 3.925 X 10-4 moles No. of moles of I2 formed after potassium iodate was added into the conical flask in part 2 = (5/1000)/5 = 0.001 moles No. of moles of I2 reacted with vitamin C = 0.001 - 3.925 X 10-4 =6.075 X 10 -4 moles So, (6.075 X 10 -4 X 10) =6.075 X 10 -3 moles of Vitamin C was present in 1 Vitamin C pill. Molar mass of Vitamin C= 176 g mol-1 So, mass of vitamin C = 176 X 6.075 X 10 -3 = 1.06g Conclusion The mass of ascorbic acid found in 1 pill of tablet is 1.06g. ...read more.

Conclusion

It should not be added too early because if we add the starch solution too early, black precipitate would be formed. The results of the experiment would thus be affected. 2. I2 vaporizes easily in air. So, to reduce the amount of iodine lost, it is wise to titrate the solution immediately. Otherwise, too much iodine would be lost and the accuracy of the results would be affected to a great extent. 3. To investigate the effect of heating on the vitamin C, Vitamin C is first dissolved in water. Then, it is heated using a Bunsen flame. Afterwards, sulphuic acid, potassium iodate, potassium iodide are added and it is titrated against sodium thiosulphate solution. To investigate the effect of being exposed to air, Vitamin C, already dissolved in acid, is left standing on a bench for 1 night. Then, it is titrated with sodium thiosulphate, with an excess of iodate and iodide added into the flask. 4. The mass of Vitamin C in 1 tablet mentioned in the specifications is 1000mg, which is equal to 1g. My results were higher than that of the specifications. This may be due to experimental errors. This may also be due to the difficulty in getting every tablet to have the exact amount of Vitamin C during the manufacturing process. ...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 Organic Chemistry section.

Found what you're looking for?

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

Here's what a star student thought of this essay

3 star(s)

Response to the question

This experimental write-up was writtenin a very logical order, with sub-titles marking all the sections to make it easy to access the information. The objective is clearly expressed at the beginning, and then the student, methodically, answers the question by ...

Read full review

Response to the question

This experimental write-up was writtenin a very logical order, with sub-titles marking all the sections to make it easy to access the information. The objective is clearly expressed at the beginning, and then the student, methodically, answers the question by showing all the phrases of the experiment, with precise explanations of why things happen. One small gripe would be that the final section with the question answers could have had a copy of the questions so it would be easier for the examiner to know whether they answered the question correctly or not.

Level of analysis

The writer has demonstrated all the necessary skills expected and it is clear that they understand the area well. The discussion section also adds some further depth to the study and shows that they are able to make evaluative comments based on both current knowledge and experience gained from doing the experiment. The calculations are all correct and lead to the correct conclusion of the amount of vitamin C in one pill. The student could have further discussed possible errors, what their implications are and how they worked to reduce them.

Quality of writing

Spelling, grammar and punctuation were all fine, with the correct technical phrases being used when necessary. All the reaction equations have been shown with experimental data and working out set out in a clear and easy to follow manner.


Did you find this review helpful? Join our team of reviewers and help other students learn

Reviewed by lookitspete 18/03/2012

Read less
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 Organic Chemistry essays

  1. Marked by a teacher

    Experiment to determine the ethanol content of wine

    5 star(s)

    The above process was repeated for solutions of ethanol up to 20% by adding 1cm3 more of ethanol while reducing the volume of water by 1cm3 at the same time, keeping the overall volumes of the solutions constant but adding 1cm3 more ethanol each time, to create solutions of 1%, 2%, 3% up to 20%.

  2. Marked by a teacher

    Determination of a Rate Equation

    3 star(s)

    N2S2O3 (cm3) Final Concentration - mol/dm3 0 50 0.4 25 25 0.2 37.5 12.5 0.1 43.75 6.25 0.05 1. Dilute 2M hydrochloric acid; measure 4cm3 of HCl and 21cm3 of distilled water in separate measuring cylinders (10 an 50ml). 2.

  1. Preparation of haloalkane. The purpose of this experiment is to prepare 2-chloro-2-methylpropane from ...

    R groups (CH3 in this experiment) are electron donating groups which disperse the charge of the carbonium ion, hence increasing the stability. Therefore, reaction through this passway is more likely to happen. 6. Strength of nucleophile Strong nucleophile such as KOH and RO- favours elimination while weak nucleophile such as ROH favours nucleophilic substitution.

  2. Free essay

    Experiment to determine the order of the reaction of Iodine with Acetone by using ...

    The contents of the flask were mixed thoroughly and the mixture was then titrated against sodium thiosulphate solution. 9. When the mixture was nearly colourless, two or three drops of a fresh starch solution were added and then the titration was continues until one drop of the sodium thiosulphate solution discharged the blue starch - iodine complex colour.

  1. the analysis of aspirin tablet

    The reaction mixture and washing were transferred to a 250 cm3 volumetric flask. 7) The reaction mixture was diluted by adding distilled water to the graduation mark of the volumetric flask. 8) The volumetric flask was inverted to make sure that the solutions inside were well mixed.

  2. Find the enthalpy change of combustion of a number of alcohol's' so that you ...

    Nevertheless there were still errors in the experiment, which may mean that the results were not completely accurate. Below is a table to show the percentage errors for instrumentation: Instrument Accuracy Point/degree of Accuracy Percentage error (%) Electronic Balance 0.01g � 0.005g 0.20 = Average (%)

  1. The aim of this experiment is to produce Aspirin. This is an estrification in ...

    Phenolphthalein indicator was used in the following reaction, because it is a suitable indicator for a titration between a weak acid and a strong alkali. Requirements * Aspirin * 100 cm3 conical flask * 95% ethanol * Pipette (10 cm3)

  2. Evaluate the most suitable vegetable oil for conversion into a biodiesel fuel.

    Using average bond enthalpies values from http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Bond-Enthalpies-718.html, the enthalpies were calculated to be as follows. The chemical formulas and bond information were taken from WolframAlpha, and the overall change in enthalpy was derived from a balanced combustion reaction equation. Table 1: Standard combustion enthalpy of some methyl ester biodiesels Methyl

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