Presence of Oxalate Ions in Guava Chemistry Investigatory Project

Presence of Oxalate ions in Guava A Chemistry Investigatory Project

Aagam 21 th (science)

Certificate This is to certify that Aagam Mundhava of class 12th(science) has satisfactorily completed the project in chemistry on Presence of Oxalate ions prescribed by the CBSE course in the academic year 2014-15. I have examined the project and hereby accord my approval of it as a study carried out and presented in the manner required for its acceptance. This does not necessarily endorse or accept every statement made or opinion expressed or conclusion drawn, but only signifies the acceptance of the project for the purpose it is submitted for.

Mrs. Kavita Kaur

Mr. Shalini Dikshit

(PGT Chemistry)

(Principal) (K.V.Vallabh Vihyanagar)

Contents o Aim of the project o Introduction o Theory o Requirements o Chemical Equations o Procedure o Observations o Calculations Conclusions

o

o Precautions o

AIM MM:

To study the presence of oxalate ions in guava fruit at different stages of ripening.

Introduction

G

uava is a common sweet fruit found in India and 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 ripening it turns yellow in color. Rich in vitamin C, this fruit is a rich source of oxalate ions whose content varies during the different stages of ripening.

many

Guavas have a pronounced and typical fragrance, similar to lemon rind but less in strength.

What is oxalate?

I

t is a carboxylic acid, primarily found in plants and animals. It is not an essential moleculeand is excreted fromour 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.

O

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.

T

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.

Requirements (A) Apparatus

100 ml measuring flask

Funnel

Pestle & Mortar

Beaker

Weighingmachine

Burette

Filter Papers

(B) Chemicals 1. dil. H2SO4

(C) Guava fruits at different stages of ripening.

Chemical Equations

2. (N/10) KMnO4 solution

Molecular Equations 2KMnO4+ 3H2SO4 HOOC-COOH.2H2O + [O]

K2SO4+ 2MnSO4+2H2O + 4[O] 600C – 700C

2CO2+ 2H2O x 5

3KMnO4+ 3H2SO4+5 HOOC-COOH.2H2O 10CO2

K2SO4+ 2MnSO4+ 18H2O +

Ionic Equations MnO4-+16H++ 5eC2O4

Mn2++ 4H2O x 2

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)Transfer 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. (7) Repeated the above experiment with 50 g of 1day, 2 day and 3 day old guava fruits.

Observations 1. 2. 3. 4. Sr No.

Weight of the guava fruit for each time was 50 g. Volume of guava extract taken for each titration was 20 ml. Normality of KMnO4 solution was (1/10). END POINT: Colour Changes to pink Guava Solution

1.

Raw

2.

Semiripened Ripened

3

Burette reading Initial 150

Final Volume Concurrent Reading of Reading KMnO4 18 132

150

13

137

150

10.8

139.2

Calculations

136.06

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 =0.581g 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 =0.603g L-1 3)

For ripened guava:

Strength of oxalate in fresh guava extract = ( 1.39/100) x 44g/litre of diluted extract = 0.612g L-1

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 = 1.39ml (b) The strength of oxalate ions of; (i) Fresh guava solution is =0.58ml

(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.

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 KMnO4attacksrubber. 4. In order to get some idea about the temperature of the solution touchthe flask with the back side of your hand. When it becomes unbearable totouch, the required temperature is reached. 5. Add about an equal volume of dil. H2SO4to the guava extract tobe titrated (say a full test tube) before adding KMnO4. 6. Read the upper meniscus while taking burette reading withKMnO4 solution. 7. In case, on addition of KMnO4a brown ppt. appears, this showsthat either H2SO4has not been added or has been added ininsufficient amount. In such a case, throw away the solutionand titrate again.

Bibliography

1. Search engines used:  www.google.com  www.wikipedia.com  www.reader.google.com  www.labs.google.com  www.quora.com 2. Practical Chemistry by Laxmi Publications. 3. The Family Encyclopedia by Dorling Kindersley.