calculation of the project "to determine the amount of ascorbic acid present in different citrus fruits"....
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Answer:
Abstract
To study and calculate the content of ascorbic acid in different citrus fruits.
Theory
Vitamin C or ascorbic acid in citrus fruits is a water soluble carbohydrate like substance involved in certain metabolic processes of animals. Although most of the animals can synthesise vitamin C, it is necessary in the diet of some including men and other primates. In order to prevent scurvy, disease characterized by haemorrhage especially in skin and mucous membranes Vitamin C was identified as a curative agent for survey in 1928. The name ascorbic acid is derived from the expression anaisearbatic vitamin, referring to vitamin’s ability to prevent and to curve scurvy. First isolated in 1928 by Hungarian biochemist and Nobel Prize winner Albert Seent Ceyorghi. Vitamin C has been the object of continued active laboratory research to determine the specific mechanism of action of cells.
Structure
Ascorbic acid (AA) is a simple sugar. It is the most active reducing agent known to occur naturally in living tissues, and is easily reversibly oxidized to Dehydroascorbic acid (DHA). Ascorbic acid is a white crystalline stable substance, when in dry light and air. It is easily soluble in water and easily oxidized especially in alkaline medium and exposure to heat and light, it reacts with metals, particularly copper. It is fairly soluble in cold acid solution. Though the first stage in its oxidation to DHA is reversible, oxidation to diketo-gulnic acid cannot be reversed.
Chemistry
1. ACIDITY
Ascorbic acid, the formula of which C6H8O6, behaves as a vinologous carboxylic acid, wherein double bond (“vinyl”) transmits electron pairs between the hydroxyl and carbonyl. There are two resonance structures for the deprotonated form, differing in the position of double bond.
2. TAUTOMERISM
Ascorbic acid is rapidly in converts into two unstable diketone tautomers by proton transfer, although it is the most stable in the enol form. The proton of the enol is lost, reacquired by electrons in the form of double bond, to produce a diketone. It is an enol reaction there are two possible forms: 1,2-diketone and 1,3-diketone.
3. DETERMINATION
The concentration of the solution of ascorbic acid can be determined in many ways; the most common way involves titration with an oxidizing agent.
DCPIP
Uses
Ascorbic acid is easily oxidized and so is used a reductant in photographic developer solutions amongst ethers and as a preservative. Exposure to oxygen, metals, light, and heat destroys ascorbic acid, so it must be stored in dark, cold and not metal container. The L-enantiomer of ascorbic acid is known as vitamin C. The name “ascorbic” comes from its property of preventing and curing scurvy.
Requirements
Water
Spirit
Starch
Iodine(solid)
Lemon Juice
Orange Juice
Citrus Maxima Juice
Burette
Pipette
Conical flask
Standard flask
Bunsen’s burner
Muslin cloth
Procedure
Weight 0.254g of solid iodine and pour in a dry beaker. Add 4g of solid potassium iodide. Then add distilled water then dissolve iodine and potassium in it. Transfer this solution to a clean 100ml volumetric flask and prepare required quantity of distilled water that was added to make 100ml of iodine solution. In this way another 100ml of iodine solution is prepared. This solution has a molarity of 0.01M.
Now a starch solution is prepared by adding a spatula of starch to 100ml of water and subsequently boiling it.
The fruit juices are extracted and filtered using muslin cloth.
The iodine solution of 0.01M is taken in a burette and 5ml of filtered juice is pippeted out in a conical flask. To the juice 1ml of starch solution is added.
The solution of juice is titrated against iodine solution. The process is stopped at the point the colour of solution in conical flask changes from fruit juice to violet colour.
Three concordant readings are taken.
Result
The following are the percentage of ascorbic acid to various citrus fruits.
Lemon juice = 31.68%
Orange juice = 49.28%
Citrus Maxima = 70.4%
Conclusions:
The percentage of ascorbic acid was found to be less in lemon juice and more in Citrus Maxima juice. Here starch solution was added to the fruit juices, before doing titration due to which some of the fruit content reacted starch and a permanent complex was formed which could not be oxidized
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