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Vitamin C Investigation.

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Introduction

´╗┐Procedure 1. Preparation of solution 1. Sodium thiosulphate 15.87g of hydrated sodium thiosulphate crystals were added to 500 ml of water and the contents mixed well until reagent dissolves giving a concentration of 0.128mole/l of Sodium thiosulphate solution. 1. Potassium iodate 0.54g of potassium iodate was added to 250ml of water and the contents mixed well until reagent dissolves giving a concentration of 0.01mole/l of potassium iodate solution. 1. Potassium iodide 8.3g of potassium iodide was added to a solution of 250ml water and the contents mixed well until reagent dissolves giving a concentration of 0.2mole/l of potassium iodide solution. 1. Concentrated sulphuric acid (1mole/l) and 1% starch solution used were premade. 1. Standardization of hydrated sodium thiosulphate 25 ml of potassium iodate solution concentration 0.01mole/l was transferred to a 250 ml flask via pipette followed by 15 ml 0.2mole/l of potassium iodide and the contents were shaken well. 5ml of concentrated 1mole/l of sulphuric acid was added turning the solution reddish brown. ...read more.

Middle

From the equation 1 above the number of moles of I2 = 3 x number of moles of Kio3. Number of moles of iodine = 3 x 0.25x10-3 moles = 7.5x10-4 moles Therefore total iodine present in the solution = 7.5x10-4 moles 2Na2s2o3 +I2 ? Na2s4o6 +2Nai 1. Verification of the procedure by titrating a solution of pure vitamin c. 0.88g of vitamin c was added to 100ml of water and the contents mixed well until reagent dissolves giving a concentration of 0.05mole/l. 25 ml of potassium iodate solution concentration 0.01mole/l was transferred to a 250 ml flask via pipette followed by 15 ml of 0.2mole/l potassium iodide and the contents were shaken well. 5ml of concentrated 1mole/l of sulphuric acid was added turning the solution reddish brown.10ml of vitamin c was transferred to the 250ml flask via pipette (the vitamin c added react in 1 to 1 ratio with the iodine present in the flask therefore decreasing the total amount of iodine in the solution).The solution is then titrated with 0.125 mole/l of hydrated sodium thiosulphate until the solution turned pale yellow(during the addition of sodium thiosulphate solution the flask was shaken well to insure proper mixing of the solution). ...read more.

Conclusion

so a rough titration was carried out to in order to become familiar with any distinct colour change which occurs at the endpoint, when the colour change for the end point was found titration was carried out again and before the end point 2 ml of starch was added and the solution was titrated till the desired colour change appears, the reading were taken and the experiment repeated until concordant result were achieved. For apple juice the same procedure was repeated only 20ml of apple juice was added to the reddish brown solution of (potassium iodate,potassium iodide and sulphuric acid )there was no difficult colour change as clear apple juice was used but to become familiar with the colour change a rough titration was carried out, when the colour change for the end point was found titration was carried out again and before the end point 2 ml of starch was added and the solution was titrated till the desired colour change appears, the reading were taken and the experiment repeated until concordant result were achieved. ...read more.

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