Estimation of Vitamin C Concentration By Titration Installation (Redox Titration Using Iodine Solution)
Estimation Of Vitamin C concentration
Safety Lab coats, safety goggles and closed-toed shoes should always be worn in the laboratory.
Introduction:- This method determines the saturation of vitamin C in a solution with redox titration using iodine.
Vitamin C, also called ascorbic acid, is an essential antioxidant needed by the human body (see additional notes).
As iodine is added during titration, ascorbic acid is oxidized to dehydroascorbic acid, while iodine is reduced to od iodide.
ascorbic acid + I2 → 2 I− + dehydroascorbic acid
As a result of this reaction, the rapidly produced iodine is reduced to iodide as long as any ascorbic acid is present.
When all the ascorbic acid is oxidized, the excess iodine is free to react with the starch index, forming a starch-blue iodine complex. This is the end of the titration.
The method is suitable for use with vitamin C supplements, fresh or packaged fruit juices and hard fruits and vegetables.
NOTE: This method is more advanced than the other method that uses potassium iodate, but since the solution of potassium iodate is more stable than iodine as a basic level, the alternative is more reliable.
Required equipment bureau and stand 100 mL or 200 mL volumetric flask 20 mL pipette 10 mL and 100 mL measuring cylinders 250 mL conical flask
Solutions Needed Iodine Solution: (0.005 mol L − 1). Measure 2 g of potassium iodide into 100 mL beaker.
Measure 1.3 g of iodine and put it in the same oven.
Add a few mL of distilled water and stir for a few minutes until iodine is dissolved.
Transfer the iodine solution to 1 L of the volumetric flask, making sure to clean all the residual solution in the volumetric flask using distilled water.
Make a solution of up to 1 L mark with distilled water.
Starch indicator solution: (0.5%). Measure 0.25 g of melted starch and pour it into 50 mL of boiling water near 100 ml of concrete flask.Stir to melt and cool before use.
How to Prepare a Sample With Vitamin C Pills: Prescribe one tablet to 200 mL of pure water (volume flask if possible).
For fresh fruit juice: Extract the juice with cheesecloth to remove seeds and pulp that may block pipettes.
Packed fruit juice: This may be necessary and filtered through cheesecloth if it contains a lot of pulp or seeds.
With fruits and vegetables: Cut a 100 g sample into small pieces and grind in a mortar and pestle.
Add 10 ml of distilled water several times while grinding the sample, each time pouring the liquid into a 100 mL volume flask.
Finally, strain the cheesecloth fruit / vegetables, wash the pulp in a few drops of 10mL of water and collect all the filters and wash in a volume flask. Dilute the extract with 100 ml of distilled water.
Alternatively a 100 g sample of fruit or vegetable may be mixed in a food processor with 50 mL of distilled water.
After mixing, strain the pulp with a cheesecloth, wash it with a few drops of 10mL of distilled water, and make the extracted solution into 100 mL in a volumetric flask.
Titration
1. Pipette aliquot 20 mL of sample solution in 250 mL of conical flask and add approximately 150 mL of distilled water and 1 mL of starch index solution.
2. Dilute the sample with iodine solution 0.005 mol L − 1.
The end of the titration is identified as a permanent sequence of blue-black color due to the complexity of starch-iodine.
3. Repeat the titration with additional aliquots in the sample solution until you get consistent results (titers consisting between 0.1 mL).
Statistics
1. Calculate the volume of iodine solution used in your concordant titers.
2. Count the reaction iodine moles.
3. Using the titration equation (below) determine the number of responsive ascorbic acid moles.
ascorbic acid + I2 → 2 I− + dehydroascorbic acid
4. Calculate the concentration in mol L − 1 of ascorbic acid in fruit / vegetable solution juice.
Also, calculate the concentration, in mg / 100mLor mg / 100g of ascorbic acid, in a fruit sample /vegetables / juice.
Additional Notes
1. Iodine contaminates the skin and clothing and therefore proper care he advised.
If contamination occurs, alcohol can be removed skin stains and detergents are found in fabric stains.
2. Vitamin C, or ascorbic acid,is a soluble substance in water an antioxidant that plays an important role in tissue protection the body from diseases and ailments.
Not done about the human body so it should be obtained from food sources -mainly fruit as well vegetables.
Chemical structure and antioxidant (reduction) action of ascorbic acid is shown in redox half equation below:
3. Concentration of prepared iodine solution can be determined more accurately by titration with a standard solution of ascorbic acid or standard potassium thiosulfate solution using starch index.
This should be done if possible as iodine solutions are uncertain.
4. Medium titre volume should be in diameter of 10 - 30 ml. If a liter is required in 20 ml
aliquot sample solution is outside this list then a large or small aliquot volume should be selected.
If the volume of the titer is too low, reduce it level.
If the volume of the titre is too high, reduce it
sample.
5. Ascorbic acid is at risk of oxidation atmospheric oxygen over time. As a result, the samples should be prepared immediately before handtitrations.
However, if the samples should be prepared a few hours in advance, oxidation can be reduced by adding a small amount oxalic acid (eg 1 g oxalic acid per 100 mL of sample solution).
6. The identification of the last place in this article most affected by the color of used sample solution.
If the solutions are color lessor pale in color, no problem identifying them
Vitamin C tablet before the last point, iodine was added mixes with ascorbic acid leaving the solution colorless.
By the end of titration all ascorbic acid has reacts and excess iodine reacts with the starch indicator it will provide pale blue color.
If iodine supplementation continues after that endpoint, another iodine-starch complex is formed in each case.
2 Commercial fruit juice before the last point, the color of the solution shows a yellowish-yellow color of the fruit juice.
At the end of the titration all ascorbic acid has reacts and any excess iodine reacts with the starch index in creates a dark blue-black complexion.
In this case the result is darker color of solution from yellow to brown-gray.
This indicates the effect of adding mL or two more iodine solution after the conclusion is reached, which leads to the formation of iodine-starch complex.
Freshly squeezed orange juice before the last point, the color of the solution reflects the bright orange color of fresh orange juice and is not affected by iodine infusion.
Once all the ascorbic acid has been oxidized, a small increase is added iodine binds to starch, providing a solution green color in this case. This is the end of the titration.
If another iodine solution were to be added, the solution the green color will be black as shown.
Red capsicum before the last point, solution retains its original color.
When all ascorbic acid is present oxidized, a slight overdose of extra iodine creates a dark complexion with a starch indicator that gives the color purple. This is the title end point.
If another mL or two of iodine should be added after the last point, the solution will enhance the dark purple the color shown here. storage space. So that juices with strong colors can be a problem with the conclusion and it is advisable to make a "hard" titration to be are familiar with any different color change which it happens in the end, (it may just be dark of the color) This will also help by establishing volume measurement of iodine solution required.
7. The above method can be used to make a number of interesting investigations about vitamin C supplementation in a variety of foods as well drinks:
• Vitamin C content of different types of fruit vegetables / juices.
• Vitamin C content of different types / varieties of vitamin pills.
• Vitamin C content in pills or food / beverage in the presence and absence of additional oxalic acid or metal ions at different times of time.
• Vitamin C content of food / drink before and after compliance with cooking conditions.
• Vitamin C content of fruits / vegetables in different stages of ripening.
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