Determination of theoxalate ions in guava fruit at different stages of its ripening. G 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 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. Guavas have a pronounced and typical fragrance, similar to lemon rind but less in strength. Guava is mainly a winter fruit. It has many medicinal properties and cultivated in almost all parts of India. Approximately composition of this fruit is Constituent Water Proteins Fats Calcium Phosphorus Vitamin ‘C’ Organic Matter % Amount 76.10 1.50 0.20 0.01 0.04 0.30 14.50 I t is a carboxylic acid, primarily found in plants and animals. It is not an essential molecule and is excreted from 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 content of the fruit is made to go into solution by boiling its pulp with distilled water and its amount in the solution is determined by redox titration using potassium permanganate solution. 5C₂O₄²¯ +16H⁺ + 2MnO₄---2Mn²⁺+ 8H₂O + 10CO₂ Pink Colourless 0.05N KMnO₄ solution, dil. H₂SO₄, distilled water, fully riped, semi-riped and raw guava. (i) Take one fully riped guava and peel off its skin. Weigh25 g of this. (ii) Make very small pieces of this with the help of a knife and crush these in clean pestle and mortar. (iii) Transfer the pulp so obtained into a 250mL beaker. Wash the pestle and mortar well with about 100mL of distilled water and transfer the washings also into the beaker. (iv) Boil the contents of the beaker for about 10 minutes. Cool and filter through a funnel. Collect the filtrate in a 250mL measuring flask. Make the volume up to the mark i.e. 250mL by adding distilled water. Label the flask as riped guava solution. (v) Similarly, prepare 250mL solution of 25g semi-riped and raw guava. (vi) Now, pipette out 25mL of solution from one of the flasks into a conical flask. Add 20mL of dilute sulphuric acid to it. Warm the flask to about 60⁰C and titrate it with 0.05 N KMnO₄ solution until colour of the solution just changes to permanent pink. Repeat the experiment with same solution till three concurrent readings are obtained. (vii) Similarly, find out the amount of 0.05 N Potassium permanganate solution required for titration in the other two guava solutions. (viii) Compare the three titre values i.e. volume of KMnO₄ consumed for 25ml of three guava solution which consumes maximum volume of the permanganate solution contains maximum oxalate ions. Observation: Normality of the KMnO₄ solution = 0.05 End Point = Colourless to pink Volume of guava solution taken each time for titration = 25mL It is concluded from the above experiment that the amount of oxalate ions in guava at different stages of ripening decreases. Precautions: (i) Do not mix the three fruits or their solutions. (ii) Boil the crushed fruit with equal amount of water and for the same length of time in all the three cases. (iii) Wash the pestle and mortar well before starting with other guavas. (iv) Weighing should be done accurately. Chemistry NCERT Book (Part-I & Part-II) Chemistry Lab Manual Comprehensive Chemistry www.scribd.com www.google.com www.wikipedia.org INDIAN INSTITUTEOF APPLIEDSCIENCE: http://www.ias.ac.in/currsci/aug102001 /248.pdf
Report "Determination of the Oxalate Ions in Guava Fruit at Different Stages of Its Ripening"