This document describes a chemistry project investigating the presence of oxalate ions in guava fruit at different stages of ripening. The project involves extracting oxalate ions from guava pulp using dilute sulfuric acid and then titrating the solution with potassium permanganate. Observations recorded the volume of potassium permanganate needed to reach the endpoint for fresh, semi-ripened, and ripened guava. Calculations determined the strength of oxalate ions increased with ripening from 0.58 g/L for fresh guava to 0.61 g/L for ripened guava. The conclusions were that the content of oxalate ions in guava was close to literature values and increased with the fruit's ripening

1. JAWAHAR NAVODAYA VIDYALAYA
ALIRAJPUR(M.P)
CHEMISTRY INVESTIGATORY
PROJECT
Arvind
Baghel
Class-12th
A

2. Certificate
his is to certifythatARVIND BAGHEL ofclass 12th
‘A’ has satisfactorily
completedthe projectin chemistry on Presenceof Oxalate ionsprescribed by
thecourse in theacademicyear 2017-18.I haveexaminedtheproject andhereby
accordmyapprovalofit as a studycarried outandpresentedin themannerrequired
forits acceptance.This does notnecessarily endorseoraccept every statementmade
oropinionexpressed orconclusiondrawn,but only signifies theacceptanceofthe
project forthepurposeit is submittedfor.
Mrs.
PGT Chemistry Principal signature
T

3. Acknowledgem
ent
I hereby acknowledgemy deep sense of gratitude
and indebtednessto Mrs. , PGT (Chemistry) whose
immense help, genius guidance, encouragement, necessary
suggestions, initiations,enthusiasm and inspirationmade this work a
master art and a joint enterprise.

4. Contents
o Aimoftheproject
o Introduction
o Theory
o Requirements
oChemicalEquations
o Procedure
o Precautions
o Observations
o Calculations
o Conclusions

5. AIM
To study the presence of oxalate ions in
guava fruit at different stages of ripening.
uava is a common sweet fruit found in India and many
other places around the world. Guavas are plants in
the Myrtle family(Myrtaceae) genus Psidium
(meaning"pomegranate"in Latin),which contains about
100 species of tropical shrub. On ripeningit turns yellow in
color. Rich in vitamin C, this fruit is a rich source of oxalate ions
whose content varies duringthe different stages of ripening.
Guavas havea pronounced and typical fragrance, similarto lemon rind but less in
strength.
What is oxalate?
t is a carboxylicacid, primarilyfound in plants and animals.It is not an essential
molecule and is excreted from our body,unchanged.Our bodyeither produces
oxalate on its own or converts other molecules like Vitamin C to oxalate.External
sources like food also contribute to the accumulation ofoxalate in ourbody. The
oxalate present in the bodyis excreted in the
form of urine as waste. Too much of oxalate
in oururine results in a
medical condition called
hyperoxaluria,commonly
referred to as kidney
stones.Diet is looked upon as a
preventivemeasure in additionto medication to treat
kidneystones.
G
I

6. Theory
xalate 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 titrand,
whose concentration is not known.
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.
he 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.
T

7. Requirements
(A)Apparatus
100 ml measuring flask Pestle & Mortar Beaker Burette
Funnel Weighing machine Filter Papers
(B) Chemicals
1. dil. H2SO4 2. (N/10)
KMnO4
solution
(C) Guava fruits at different
stages of ripening.

8. CHEMICAL EQUATIONS
MOLECULAR EQUATIONS
2KMnO4+ 3H2SO4  K2SO4+ 2MnSO4+2H2O + 4[O]
HOOC-COOH.2H2O + [O] 600C – 700C 2CO2+ 2H2O x 5
3KMnO4+ 3H2SO4+5 HOOC-COOH.2H2O 
K2SO4+ 2MnSO4+ 18H2O +10CO2
IONIC EQUATIONS
MnO4-+16H++ 5e-  Mn2++ 4H2O x 2
C2O4  2CO2+ 2e-x 5
2MnO4-+ 16H++ 5C2O42-  2Mn2++8H2O + 10CO2
Procedure
(1)Weighed 50 g of fresh guava and crushed it to a fine pulp using
pestle and mortar.
(2)Transferred the crushed pulp to a beaker and added about 50 ml
dilute H2SO4 to it.
(3)Boiled the content for about 10 minutes. Cooled and filtered the
contents in a 100 ml measuring flask.
(4)Made up the volume 100 ml by adding ample amount of distilled
water.
(5)Took 20 ml of the solution from the flask and added 20 ml of dilute
sulphuric acid to it.
(6)Heated the mixture to about 600 C and titrated it against (n/10)
KMnO4 solution taken in a burette till the end point had an
appearance of pink colour.

9. (7) Repeated the above experiment with 50 g of 1day, 2 day and 3 day
old guava fruits.
Precautions
1.There should be no parallax while taking measurements.
2.Spillage of chemicals should be checked.
3. Avoid the use of burette having a rubber tap as KMnO4attacks
rubber.
4. 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.
5. Add about an equal volume of dil. H2SO4 to the guava extract
to be titrated (say a full test tube) before adding KMnO4.
6. Read the upper meniscus while taking burette reading with
KMnO4 solution.
7. 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.
Observations
1. Weight of the guava fruit for each time was 50 g.
2. Volume of guava extract taken for each titration was 20 ml.
3. Normality of KMnO4 solution was (1/10).
4. END POINT: Colour Changes to pink

10. Guava
Solution
Burette
reading
Initial
Final
Reading
Volume of
KMnO4
Concurrent
Reading
Raw 150 18 132
136.06
Semi-
ripened
150 13 137
Ripened 150 10.8 139.2
Calculations
1) For raw guava
N1V1 = N2V2
N1 x 10 = (1/10) x132
1/10 x Normality of oxalate = (x/100) = 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 g L-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 g L-1
3) For ripened guava
Strength of oxalate in fresh guava extract
= ( 1.39/100) x 44g/litre of diluted extract
= 0.612 g L-1

11. Results
(a) The normality of oxalate ions of;
(i) Fresh guava solution is = 1.32 ml
(ii) Semi-ripen guava solution is = 1.37 ml
(iii) Ripened guava solution is = 1.39 ml
(b) The strength of oxalate ions of;
(i) Fresh guava solution is = 0.58 ml
(ii) Semi-ripened guava is = 0.60 ml
(iii) Ripened guava is = 0.61 ml
Conclusions
The content of oxalate ions in guava was found to be 59.67 per cent,
which is close to the literature value of 60 percent.
It was also noticed that the content of oxalic ions grows with ripening
of guava.