Post on 02-Jun-2018
transcript
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 1/19
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 2/19
TABLE OF CONTENTS
Certificate
Acknowledgements
INTRODUCTION.......................................................................................................
.......................1
Structure.......................................................................................................................
.................2
Biological
Purpose.................................................................................................................3
Acidity.........................................................................................................................
..................4
Oxidation.....................................................................................................................
................4
Factors affecting rate of oxidation of Ascorbic acid..............................5
Explanation of
titration..................................................................................................5
EXPERIMENT............................................................................................................
..........................6
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 3/19
TABULATION...........................................................................................................
.........................8
CONCLUSION...........................................................................................................
........................12
TIME
RECORD.....................................................................................................................
..............13
SCOPE FOR FURTHER
INVESTIGATION.............................................................14
BIBLIOGRAPHY.......................................................................................................
.........................15
ACKNOWLEDGEMENTS
This project would not have been possible without the support and guidance of our
teacher Mr. Jaganatha Shenoy, our laboratory in-charge teacher Mrs. Sudha and the
laboratory assistants, who were always there to give us a helping hand and sort out the
nuances of the procedures, experimentation and Chemistry.
I would also like to thank the Principle of our school, Mrs. Sumitra Das, and the school
itself, for providing us an conducive environment for the study and pursuit of ideas.
Finally, I thank the Central Board of Secondary Education for incorporating the
experimentally rigorous parts of the Chemistry into our curriculum so that we may
graduate with an all-round knowledge of the subject, and be better prepared in pursuing
multidisciplinary endeavours in the future.
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 4/19
INTRODUCTION
Ascorbic acid is a naturally occurring organic compound with antioxidant properties. It
is a white solid, but impure samples can appear yellowish. It dissolves well in water to
give mildly acidic solutions. Ascorbic acid is one form of vitamin C. It was originally
called L-hexuronic acid. The new name, ascorbic acid, is derived from a- (meaning "no")
and scorbutus (scurvy), the disease caused by a deficiency of vitamin C. Because it is
derived from glucose, many animals are able to produce it, but humans require it as
part of their nutrition.
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 5/19
Structure
Molecular Formula: C6H8O6 Molecular Mass: 176
IUPAC name: (5R)-[(1S)-1,2-dihydroxyethyl]-3,4-dihydroxyfuran-2(5H)-one
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 6/19
The Ascorbic acid molecule contains four hydroxyl groups present in positions 2,3,5,6;
the -OH group in position 3 is acidic (pKa = 4.3), the hydroxyl group in position 5 has
pKa = 11.2, while those in position 5 and 6 act as secondary and primary alcohol residue
respectively.
It exhibits tautomerism, where the C1=O and the C3-OH groups interchange with the
shift of double bond.
Biological Purpose
Ascorbic acid is required for the growth and repair of tissues in all parts of your body. Ithelps the body make collagen, an important protein used to make skin, cartilage, tendons,
ligaments, and blood vessels. Vitamin C is needed for healing wounds, and for repairing
and maintaining bones and teeth.
It is an antioxidant, and it blocks some of the damage caused by free radicals,
substances that damage DNA. The build-up of free radicals over time may contribute to
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 7/19
the aging process and the development of health conditions such as cancer, heart disease,
and arthritis.
The Reichstein-Grüssner synthesis of ascorbic acid provides a supply of pure
crystalline ascorbic acid for industrial uses; it also makes a person’s requirements of daily
ingest manageable. Because of the extent of its use and humans´ need for ascorbic acid,
the
chemistry of the oxidation of this compound merits thorough research. It has been
suggested that, when added to processed foods as a means of improving its beneficial
properties, ascorbic acid’s tendency to act as a reducing agent results in numerous
derivatives whose toxicity is (unlike that of ascorbic acid) such as in synthetic drinks is,
controversial yet partially supported by evidence..
Acidity
Ascorbic acid is classed as a reductone. The ascorbate anion is stabilized by electron
delocalization, through resonance. It has two canonical forms. For this reason, ascorbicacid is much more acidic than would be expected.
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 8/19
Oxidation
Ascorbic acid is sensitive to heating, to light, and to the action of oxidizing agents and
metal ions. It is readily oxidized in aqueous solutions by reacting with atmospheric
oxygen, and behaves as a electron pair donor.
The deprotonation of ascorbic acid is given by the following equilibrium:
This results in semihydroascorbic acid, which then releases another proton when it gives
off an electron pair to a present oxidant.
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 9/19
Ascorbic acid loses a proton because the electron pair is transferred to the more
electronegative oxygen. This leads to the first equilibrium between ascorbic acid and
semihydroascorbic acid. The enol group on ascorbic acid becomes an enolate groupafter the deprotonation. The second equilibrium is a result of electron movement
because of the delocalization that occurs in the dicarbonyl system (a carbonyl functional
group is a carbon atom sharing an electron pair with an oxygen atom). The fact that
delocalization occurs could be because the system is conjugated (there are alternating
double and single covalent bonds from one carbonyl group to the other).
The negative charge on the oxygen atom of semihydroascorbic (due of delocalization of
charge) becomes a π bond between carbon and oxygen, which then results in two new
carbonyl groups because oxygen cannot have a second σ bond, and so must therefore give
off the σ electrons, in this case to an oxidant X+ . The breaking of the σ bond implies that
the hydrogen atom is given off. The electron movement in the second equilibrium results
in a neutrally charged compound, dehydroascorbic acid.
It can be concluded that the oxidation of ascorbic acid involves the loss of
two electrons and two protons. One can then write the oxidation of ascorbic acid by
oxygen as follows:
Factors affecting rate of Oxidation of Ascorbic Acid
1. Concentration of oxygen [O2].
2. Temperature3. Catalysts:
a. The enzyme ascorbic acid oxidase catalyses the oxidation of ascorbic acid.
b. Transition metal ions increase the rate of oxidation.
4. Acidity: the rate of oxidation of ascorbic acid is greater in a neutral or basic
medium.
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 10/19
Explanation of Titration
The traditional way to analyze the ascorbic acid content is the process of titration, with
an oxidizing agent. Several procedures have been developed, mainly relying
on iodometry. Iodine is used in the presence of a starch indicator. Iodine is reduced by
ascorbic acid, and, when all the ascorbic acid has reacted, the iodine is then in excess,
f forming a blue-black complex with the starch indicator. This indicates the endpoint of
the titration. As an alternative, ascorbic acid can be treated with iodine in excess,
followed by back titration with sodium thiosulfate using starch as an indicator.
Experiment
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 11/19
Aim: To prepare N/10 solution of Iodine, and use this solution to find the concentration
of ascorbic acid present in citrus fruits.
Materials Used: Electronic balance, conical flask, standard flask, burette, pipette, iron
stand, white tile, test tubes, Iodine crystals, distilled water, starch indicator.
Theory:
Preparation of Standard solution
Iodine : I2
Molar Mass : 252 g mol-1
Equivalent mass : 126 g equivalent-1
To prepare 1l of N/10 solution of Iodine, 12.6g is required. To prepare 100 ml of N/10
Iodine solution,
12.6/10 = 1.26g
is required.
Law of equivalents: It states that the number of equivalents of substance to be titrated is
equal to the number of equivalents of titrant used.
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 12/19
Mathematically,
N1V1=N2V2
Chemical equation
C6H8O6→ C6H6O6 + 2H+ + 2e-
I2 + 2e-→2I
-
C6H8O6 + I2→ C6H6O6 + 2H+ + 2I-
Procedure
➢ 100 ml of N/10 Iodine solution was prepared by dissolving 1.26g of iodine crystals
in 100 ml of distilled water in a standard flask.
➢ The pipette and conical flask were rinsed with the citrus fruit juice.
➢ The burette was rinsed and filled with the prepared Iodine solution.
➢ 10 ml of the fruit juice was taken in the conical flask, and a few drops of starch
indicator were added.
➢ The Iodine solution was added dropwise to the titration flask till the colourless
solution turned blue black. The initial and final reading of the burette were noted. ➢ The experiment was repeated till two concordant readings were obtained.
➢
Observation
→ Burette solution : N/10 Iodine solution
→ Conical flask solution : Fruit juice
→
Indicator : Starch indicator
→ End point : Colourless → Blue Black
TABULATION
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 13/19
1.
Orange juice
BURETTE
READING
VOL OF JUICE
TAKEN(ml)
FINAL
VOLUME(ml)
INITIAL
VOLUME(ml)
VOLUME
USED(ml)
1.4 0 1.4 10
2.6 1.4 1.2 10
3.4 2.6 1.2 10
Concordant reading : 1.2 ml
Calculations
N1V1=N2V2
1 - Iodine solution
2 - Orange juice
N1 = N/10 V1 = 1.2ml V2= 10ml N2=x
N/10×1.2=x×10
N2=0.012 N
2.
Lime juice
BURETTE
READING
VOL OF JUICE
TAKEN(ml)
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 14/19
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 15/19
6.2 5.8 0.4 10
6.5 6.2 0.3 10
6.8 6.5 0.3 10
Concordant reading : 0.3 ml
Calculations
N1V1=N2V2
1 - Iodine solution
2 - Synthetic drink
N1 = N/10 V1 = 0.3ml V2 = 10ml N2=x
N/10×0.3=x×10
N2=0.003 N
4.
Grape juice
BURETTE
READING
VOL OF JUICE
TAKEN(ml)
FINAL
VOLUME(ml)
INITIAL
VOLUME(ml)
VOLUME
USED(ml)
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 16/19
0.7 0 0.7 10
1.3 0.7 0.6 10
1.9 1.3 0.6 10
Concordant reading : 0.6 ml
Calculations
N1V1=N2V2
1 - Iodine solution
2 - Grape juice
N1=N/10 V1=0.6ml V2=10ml N2=x
N/10×0.6=x×10
N2=0.006 N
CONCLUSION
The given samples of fruit juice were analysed, and the highest concentration of ascorbic
acid was found to be present in orange juice, while the lowest concentration was found to
be present in synthetic drink. The second highest concentration was found to be in lime
juice followed by grape juice.
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 17/19
TIME RECORD
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 18/19
SCOPE FOR FURTHER
INVESTIGATION
A paradox in metabolism is that, while the vast majority of complex life on
Earth requires oxygen for its existence, oxygen is a highly reactive molecule that
damages living organisms by producing reactive oxygen species. Consequently,
organisms contain a complex network of antioxidants and enzymes that work together to
prevent oxidative damage to cellular components. However, reactive oxygen species also
have useful cellular functions, such as redox signaling. Thus, the function of antioxidant
systems is not to remove oxidants entirely, but instead to keep them at an optimum level.
These oxidants can damage cells by oxidizing DNA or proteins. Damage to DNA can
cause mutations and possibly cancer, if not reversed by DNA repair mechanisms, while
damage to proteins causes enzyme inhibition and protein degradation.
Ascorbic acid is one important antioxidant required by both plants and animals. As one of
the enzymes needed to make ascorbic acid has been lost
by mutation during primate evolution, humans must obtain it from the diet; it is therefore
a vitamin. Therefore, the study of oxidation of ascorbic acid is vital to help control the
aforementioned diseases and cure them.
8/10/2019 Volumetric Analysis of Ascorbic Acid Present in Citrus Fruits
http://slidepdf.com/reader/full/volumetric-analysis-of-ascorbic-acid-present-in-citrus-fruits 19/19
BIBLIOGRAPHY
1.
Wikipedia
2.
Khan Academy
3.
http://chemed.chem.purdue.edu/genchem/lab/techniques/titration/ 4.
http://www.dartmouth.edu/~chemlab/techniques/titration.html
5. http://chemwiki.ucdavis.edu/Analytical_Chemistry/Quantitative_Analysis/Titratio
n
6.
Youtube
7.
Google Images