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Topic: iodometric back titration of vitamin C  (Read 2020 times)

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Offline jasonpontus

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iodometric back titration of vitamin C
« on: October 26, 2019, 04:54:39 AM »
In the iodometric back titration experiment to determine the content of vitamin C, our professor asked us why is there a specific order to add reagents during the Standardization of Sodium Thiosulphate Solution & Determination of the Vitamin C content of the tablet to the conical flask?

A) Standardization of Sodium Thiosulphate Solution.
1. Pipette 25.00 cm3 potassium iodate(V) to the conical flask.
2. Then, add 5 cm3 of 1.0M potassium iodide solution to the conical flask.
3. After that, add 10 cm3 of 0.5M sulphuric acid to the conical flask.
4. Titrate the mixture with sodium thiosulphate.

B) Determination of the Vitamin C content of the tablet
1. Dissolves the vitamin C tablet in the 0.5M sulphuric acid.
2. Add 5cm3 of 1.0M potassium iodide.
3. Pipette 25.00cm3 of potassium iodate(V) into the mixture.
4. Titrate the mixture with sodium thiosulphate.

Why is there a difference between the sequence of adding reagents of A and B?
What is the consequence if we don't follow the sequence?
Thank you very much!!!



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Offline Borek

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Re: iodometric back titration of vitamin C
« Reply #1 on: October 26, 2019, 06:10:14 AM »
Can you write equations of the reactions involved?

Can you think what side reactions could take place?
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Offline chenbeier

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Re: iodometric back titration of vitamin C
« Reply #2 on: October 26, 2019, 07:31:11 AM »
The sample  has to be treated as described in b otherwise side reaction can take place.. But I dont see any reason to follow the order in a. The blank can be treated like the sample in b in my opinion.
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Offline jasonpontus

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Re: iodometric back titration of vitamin C
« Reply #3 on: October 26, 2019, 10:19:43 AM »
Quote from: chenbeier on October 26, 2019, 07:31:11 AM
The sample  has to be treated as described in b otherwise side reaction can take place.. But I dont see any reason to follow the order in a. The blank can be treated like the sample in b in my opinion.
Can I ask what side reaction will take place if i don't follow the order in B?
thx a lots!!
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Offline chenbeier

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Re: iodometric back titration of vitamin C
« Reply #4 on: October 26, 2019, 12:17:43 PM »
What kind of substace is iodate and Vitamin C. What would happen if mix before?
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Offline jasonpontus

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Re: iodometric back titration of vitamin C
« Reply #5 on: October 27, 2019, 03:47:40 AM »
Quote from: chenbeier on October 26, 2019, 12:17:43 PM
What kind of substace is iodate and Vitamin C. What would happen if mix before?
Iodate is a strong oxidizing agent and vitamin C is a reducing agent. So, if they put together vitamin C will be oxidized, right? Is my explanation correct?
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Offline chenbeier

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Re: iodometric back titration of vitamin C
« Reply #6 on: October 27, 2019, 06:46:17 AM »
Correct. You got it.
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Offline jasonpontus

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Re: iodometric back titration of vitamin C
« Reply #7 on: October 27, 2019, 10:15:58 AM »
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