INVESTIGATORY PROJECT – CHEMISTRY
The amount of Oxalate ions in Guava Fruits in different
stages of ripening
For the partial fulfilment of the conditions laid down for
AISSCE [2022-23]
SUBMITTED BY:
NAME: SUCHISMITA KHUNTIA
CLASS: XII-(B)
ROLL NO:
Under the guidance of:
Mr. Rajesh Ghosh
PGT, Chemistry
ACKNOWLEDGEMENT
I would like to profound sense of gratitude to my guide Mr.
Rajesh Ghosh, my Chemistry teacher for his valuable guidance
and suggestions during preparation of my project work.
I am grateful to my principal Dr. Pratap Badapanda, for his
encouragement and constant inspiration.
With great pleasure, I also extend my gratitude to my parents,
other family members and friends for their support which
enabled me to finish this piece of work successfully.
pg. 2
DECLARATION
I, Suchismita Khuntia, a student of Class-XII ‘B’ of COHEN
INTERNATIONAL SCHOOL, Haridamada hereby submit the
project entitled "The amount of Oxalate ions in Guava Fruits
in different stages of Ripening" for the Chemistry project of
AISSCE 2022-2023. This project consists of original work done
by me under the able guidance and supervision of my Chemistry
teacher.
_______________________________________
(Student)
pg. 3
CERTIFICATE
This is to certify that the project entitled " The amount of
Oxalate ions in Guava Fruits in different stages of Ripening "
is an original piece of work done by Suchismita Khuntia, of
Class-XII; Sec-B is in accordance with the topic allotted to him.
This project is submitted towards the partial fulfilment of the
conditions laid down for AISSCE 2022-2023 and embodies the
work done by him under my higher authority’s guidance and
supervision.
(Internal Examiner) (External Examiner)
(Principal)
pg. 4
CONTENT
Particulars Page No.
Introduction 6
Objectives & Theory 7-8
Materials Required 9-10
Procedure 11
Precaution 12
Observation 13
Calculation 14
Result & Conclusion 15
Bibliography 16
pg. 5
INTRODUCTION
➢ Guava is a common sweet fruit found in India and many other
places around the world. Guavas are plants in the Myrtle family
(Myrtaceous) genus Psidium (meaning “pomegranate” in
Latin), which contains about 100 species of tropical shrub. On
ripening it turns yellow in colour. Rich in vitamin C, this fruit
is a rich source of oxalate ion whose content varies during the
different stages of ripening.
➢ Guavas have a pronounced and typical fragrance, similar to
lemon rind but less in strength.
pg. 6
OBJECTIVE
To study the presence of oxalate ion in guava fruit at different
stages of ripening.
WHAT IS OXALATE?
➢ It is a carboxylic acid, primarily found in plants and animals. It
is not an essential molecule and is excreted form our body,
unchanged. Our body either produces oxalate on its own or
converts other molecules like vitamin C to oxalate.
➢ External sources like food also contribute to the accumulation
of oxalate in our body. The oxalate present in the body is
excreted in the form of urine as waste.
➢ Too much of oxalate in our urine results in a medical condition
called hyperoxaluria, commonly referred to as kidney stones.
Diet is looked upon as a preventive measure in addition to
medication to treat kidney stones.
➢ Oxalate ions are extracted from the fruit by boiling pulp with
dilute H2SO4. The oxalate ions are estimated volumetrically, by
titrating the solution with KMnO4 solution.
➢ A reagent, called the titrant, of a known concentration (a
standard solution and volume is used to react with a solution of
the analyte or titrant, whose concentration is not known.
pg. 7
➢ Using a calibrated burette or chemistry pipetting syringe to add
the titrant, it is possible to determine the exact amount that has
been consumed when the endpoint is reached.
➢ The endpoint is the point at which the titration is complete, as
determined by an indicator. This is ideally the same volume as
the equivalence point.
➢ The volume of added titrant at which the number of moles of
titrant is equal to the number of moles of analyte, or some
multiple thereof (as in polyprotic acids). In the classic strong
acid-strong base titration, the endpoint of a titration is the point
at which the pH of the reactant is just about equal to 7, and often
when the solution takes on a persisting solid colour as in the
pink of phenolphthalein indicator.
Constituents % Amount
Water 76.10
Proteins 1.50
Fats 0.20
Calcium 0.01
Phosphorous 0.04
Vitamins C 0.03
Organic matter 14.50
pg. 8
MATERIALS REQUIRED
(a) Apparatus
• 100ml measuring flask burette
• Pestle & Mortar
• Beaker
• Funnel
• Papers
• Weighing machine
• Filter
(b) Chemicals
• (N/10) Potassium Permanganate (KMnO4)
• Dil. H2SO4.
pg. 9
(c) Guava fruits at different stages of ripening,
Chemical equations:
2KMnO4 + 3H2SO4 → K2SO4 + 2MnSO4 + 2H2O + 4[O]
HOOC - COOH.2H2O + [O] → 2CO2 + 2H2O x 5
____________________________________________________
2KMnO4 + 3H2SO4 + 5HOOC-COOH.2H2O → K2SO4 +
2MnSO4 + 18H2O + 10CO2
Ionic equation:
MnO4- + 16H+ + 5e- → Mn2+ + 4H2O x 2
C2O4 2-→ 2CO2 + 2e- x 5
2MnO4- + 16H+ + 5C2O42- → 2Mn2+ + 8H2O + 10CO2
pg. 10
PROCEDURE
➢ Weighed 50 g of fresh guava and crushed it to a fine pulp
using pestle and mortar.
➢ Transferred the crushed pulp to a beaker and added about 50
ml dilute H2SO4 to it.
➢ Boiled the content for about 10 minutes. Cooled and filtered
the contents in a 100 ml measuring flask.
➢ Made up the volume 100 ml by adding ample amount of
distilled water.
➢ Took 20 ml of the solution from the flask and added 20 ml of
dilute sulphuric acid to it.
➢ Heated the mixture to about 60°C and titrated it against (N/10)
KMnO4 solution taken in a burette till the end point had an
appearance of pink colour.
➢ Repeated the above experiment with 50 g of 1-day, 2-day and
3-day old guava fruits.
pg. 11
PRECAUTIONS
➢ There should be no parallax while taking measurements.
➢ Spillage of chemicals should be checked.
➢ Avoid the use of burette having a rubber tap as KMnO4
attacks rubber.
➢ In order to get some idea about the temperature of the
solution touch the flask with the back side of your hand, when
it becomes unbearable to touch the required temperature is
reached.
➢ Add about an equal volume of dil H2SO4 to the guava extract
to be titrated (say a full test tube) before adding KMnO4 .
➢ Read the upper meniscus while taking burette reading with
KMnO4 solution.
➢ In case, on addition of KMnO4 a brown ppt. appears, this
shows that either H2SO4 has not been added or has been
added in insufficient amount. In such a case, throw away the
solution and titrate again.
pg. 12
OBSERVATIONS
➢ Weight of the guava fruit for each time was 50 g.
➢ Volume of guava extract taken for each titration was 10 ml.
➢ Normality of KMnO4 solution was (1/10).
➢ End point: Colour changes to PINK.
Guava Burette Final Vol. of Concordant
Solution reading Reading KMnO4 reading
(initial)
Raw 150 18 132
Semi-
ripened 150 13 137 136.06
Ripened 150 10.8 139.2
pg. 13
CALCULATION
1. For Raw Guava:
» N1V1 = N2V2
» N1 x 10 = (1/10) x 132
» N1 = 132/100 = 1.32
» Strength of oxalate in fresh guava extract
= normality x Eq. mass of oxalate ion
= 1.32/100 x 44g/litre of diluted extract
= 0.581 gL-1
2. For Semi-ripened guava (1-day old)
» Strength of oxalate in one day old guava extract
= 1.37/100 x 44g/litre of diluted extract
= 0.603 gL-1
3. For Ripened Guava
» Strength of oxalate in ripened guava extract
= 1.39/100 x 44g/litre of diluted extract
= 0.612 gL-1
pg. 14
RESULTS
1. The Normality of oxalate ions of:
➢ Fresh Guava solution is = 1.32 N
➢ Semi-Ripen Guava solution is = 1.37 N
➢ Ripened Guava solution is = 1.39 N
2. The Strength of Oxalate ions of:
➢ Fresh guava solution is = 0.58 gL-1
➢ Semi - ripen guava solution is = 0.60 gL-1
➢ Ripened guava solution is = 0.61 gL-1
CONCLUSION
✓ The content of oxalate ion in guava was found to be 59.67%,
which is close to the literature value of 60%.
✓ It was also noticed that the content of oxalate ion grows with
ripening of guava.
pg. 15
BIBLIOGRAPHY
• http://www.cbseportal.com
• wikipedia.com
• chemicalland.com
• books.google.co.in
pg. 16
