My vitamin C titration with iodate turned red. Help

  • Thread starter Mingrulz34
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In summary, the speaker conducted an experiment where they dissolved a vitamin C tablet in water and added potassium iodide, hydrochloric acid, and starch. They then titrated the solution with potassium iodate to determine the concentration of vitamin C. However, the endpoint did not match their expectations and the solution turned red. After seeking help, they realized that the starch had not fully dissolved due to not heating the water beforehand. Once the starch solution was heated, the experiment was successful.
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Mingrulz34
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So for my IA, I dissolved a 1000mg vitamin c tablet in 355mL of water, took 20mL of it and diluted it to 100mL making it about 0.0032mol/L. I then added 5mL of 0.5mol/L potassium iodide, 5mL of 1.0mol/L hydrochloric acid and some 6 drops of 1 gram of starch dissolved in 100mL of water.

I then titrated that entire sample with potassium iodate to determine the concentration of vitamin c. The endpoint was suppose to be when the solution turned blue (iodine+starch) but it ended up slowly turning yellow and then becoming darker until it eventually turned red. I tried increasing the concentration of potassium iodate but it just lead to the solution becoming red faster. I think I should have enough I had quit my IA and am excpected to redo it sometime later. Does anyone have any idea what has happened to my experiment? Any help would be appreciated. Thanks!
 
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Mingrulz34 said:
IA,
What is "IA?"
 
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The color you describe is that of a free iodine dissolved in water. Sounds like it doesn't react with neither ascorbic acid nor the starch, as if they were not present in the solution.
 
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Thanks! It turned out that I didn't heat up the water before dissolving the starch in it. This led most of the starch not dissolving and settling on the bottom where it was unable to react with the iodine being formed at the top. Once I heated the starch solution, it worked fine!
 

1. How does the vitamin C titration with iodate method work?

The vitamin C titration with iodate method is a common laboratory technique used to determine the concentration of vitamin C in a solution. This method involves the reaction between iodate ions and vitamin C, which produces iodine. The iodine then reacts with starch to form a blue-black complex, which indicates the endpoint of the titration. By measuring the amount of iodine produced, the concentration of vitamin C in the solution can be calculated.

2. Why did my vitamin C titration with iodate turn red?

If your vitamin C titration with iodate turned red, it is likely that you have overshot the endpoint of the titration. This can happen if you added too much iodate solution or if the solution was not well mixed. The red color indicates that there is still unreacted iodine present in the solution. To avoid this, it is important to carefully add the iodate solution and to mix the solution thoroughly before adding more.

3. How can I ensure accurate results in my vitamin C titration with iodate?

To ensure accurate results in your vitamin C titration with iodate, it is important to carefully measure and record the volume of iodate solution added. It is also crucial to mix the solution thoroughly before each addition of iodate solution. Using standardized solutions and performing multiple trials can also help to improve accuracy.

4. Can I use this method to determine the vitamin C content in food or supplements?

Yes, the vitamin C titration with iodate method can be used to determine the vitamin C content in food or supplements. However, it is important to note that this method only measures the total amount of vitamin C present, including both the active form (ascorbic acid) and the oxidized form (dehydroascorbic acid). Other methods, such as high-performance liquid chromatography, may be used to specifically measure ascorbic acid content.

5. Are there any limitations to the vitamin C titration with iodate method?

Yes, there are some limitations to the vitamin C titration with iodate method. This method is only suitable for measuring vitamin C concentrations in the range of 0.1-1.0 mg/mL. Additionally, the method may not be accurate if the sample contains other substances that can react with iodate or interfere with the color change of the starch indicator. It is important to carefully choose a sample preparation method and to account for any potential interferences in order to obtain accurate results.

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