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Topic: [Lab] Determination of vitamin C in a fruit juice  (Read 2527 times)

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Offline katkal

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[Lab] Determination of vitamin C in a fruit juice
« on: January 28, 2014, 11:33:10 AM »
Hello, I was wondering if someone could help me with the general steps of my chem lab. We will be using an iodometric titration to determine vitamin C content in a fruit juice. Here are my general steps:

  • Weight out KIO3
  • Dilute KIO3 in volumetric to mark with water
  • Fill buret with KIO3, record volume
  • In erlenmeyer pipet needed amount of juice to be analyzed
  • Add HCl, KI, and a starch indicator, dilute with water so endpoint is easier to see
    Titrate to endpoint and repeat until two total volumes agree within 0.15mL

Does that sound about right?

Thanks :)

Offline Hunter2

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Offline katkal

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Re: [Lab] Determination of vitamin C in a fruit juice
« Reply #2 on: January 28, 2014, 02:52:56 PM »
Do you think you could tell me what specifically looks wrong with mine? I have actually read over that page many times, I was just looking for some input on my interpretation of it. Thanks!

Offline Hunter2

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Re: [Lab] Determination of vitamin C in a fruit juice
« Reply #3 on: January 28, 2014, 02:58:36 PM »
The key is you have a iodine solution ready. In your case you have iodate in your burette.

Offline Borek

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Re: [Lab] Determination of vitamin C in a fruit juice
« Reply #4 on: January 28, 2014, 05:25:01 PM »
Do you think you could tell me what specifically looks wrong with mine?

As far as I can tell - nothing. There are many ways to skin that cat, and titration with iodate solution is one of them.

That being said, I am not entirely sure it is the best method. I was always under impression reaction between iodide and iodate is slightly too slow, which is why it is better to use it to prepare iodine solution first, then to add reducing agent and finally titrate excess iodine with thiosulfate.

Or at least, all classical analytical chemistry books I learned from had always suggested this approach, and I always assumed they knew better.
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Offline katkal

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Re: [Lab] Determination of vitamin C in a fruit juice
« Reply #5 on: January 28, 2014, 10:07:13 PM »
Yeah, the similar experiments I have seen all followed a method similar to that. I think we are doing this way because they don't expect us to be able to finish all of the titrations we are supposed to do (first year lab...)

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