비타민 C 정량분석. 시약 제조, 적정 및 계산

비타민 C 정량분석. 시약 제조, 적정 및 계산

Vitamin C Determination by Iodine Titration

 

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▶ 1% Starch Indicator Solution

1) Add 0.5 g soluble starch to 50 mL near-boiling distilled water.

(0.5 / 50.5) * 100 = 0.99%

2) Mix well and allow to cool before use. (doesn't have to be 1%; 0.5% is fine)

 

 

▶ Iodine Solution

1) Dissolve 5 g potassium iodide (KI) and 0.268 g potassium iodate (KIO3) in 200 mL of distilled water.

2) Add 30 mL of 3 M sulfuric acid.

3) Pour this solution into a 500 mL graduated cylinder and dilute it to a final volume of 500 mL with distilled water.

4) Mix the solution.

5) Transfer the solution to a 600 mL beaker. Label the beaker as your iodine solution.

 

 

▶ Vitamin C (ascorbic acid) Standard Solution

1) Dissolve 0.25 g vitamin C (ascorbic acid) in 100 mL distilled water.

2) Dilute to 250 mL with distilled water in a volumetric flask. Label the flask as your vitamin C standard solution.

0.25 g / 250 mL = 0.25 g / 0.250 L = 1 g/L

 

 

▶ Standardizing Solutions

1) Add 25 mL of vitamin C standard solution to a 125 mL Erlenmeyer flask.

2) Add 10 drops of 1% starch solution.

3) Rinse your buret with a small volume of the iodine solution and then fill it. Record the initial volume.

4) Titrate the solution until the endpoint is reached. This will be when you see the first sign of blue color that persists after 20 seconds of swirling the solution.

5) Record the final volume of iodine solution. The volume that was required is the starting volume minus the final volume.

6) Repeat the titration at least twice more. The results should agree within 0.1 mL.

 

 

▶ Titration Calculations

1) Calculate the mL of titrant used for each flask. Take the measurements you obtained and average them.

average volume = total volume / number of trials

2) Determine how much titrant was required for your standard.

If you needed an average of 10 mL of iodine solution to react 0.25 g of vitamin C, then you can determine how much vitamin C was in a sample. For example, if you needed 6 mL to react your juice:

10 mL iodine solution : 0.25 g Vit C = 6 mL iodine solution : ? g Vit C

? = 0.25 * 6 / 10 = 0.15 g Vit C in that sample

3) Keep in mind the volume of your sample, so you can make other calculations, such as grams per liter. For a 25 mL juice sample, for example:

0.15 g / 25 mL = 0.15 g / 0.025 L = 6 g/L of vitamin C in that sample

 

 

[ 출처 : http://chemistry.about.com/od/demonstrationsexperiments/ss/vitctitration.htm ]

 

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volume of vitamin C standard solution = volume of juice sample = 25 mL
1 g/L : 10 mL = ? g/L : 6 mL
? = 1 * 6 / 10 = 0.6 g/L Vit C in that sample
0.6 g/L * 25 mL = 0.6 g/L * 0.025 L = 0.015 g Vit C in that sample

 

 

 

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