kierracov
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Chemistry Project Topic

Postby kierracov » Sun Jan 13, 2019 3:35 pm

Hi there,
I am a grade 11 IB student in SL Chemistry. I will be starting my II (Internal Investigation) soon and I was wondering if this would be a good topic: determining the content of sugar in different fruits using redox titration. Specifically, glucose and fructose, as I have read that the safest fruits are those that are high in glucose and low in fructose. Do you think this would be feasible? Any suggestions for improvement or a completely different idea?

I would like to do my project on titration specifically as our two options are titration or calorimetry and I am not very confident in the latter.
Thanks!

norman40
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Re: Chemistry Project Topic

Postby norman40 » Mon Jan 14, 2019 4:33 pm

Hello,

Determining the glucose and fructose in various fruits is a great topic. Analysis of both sugars in the presence of others in fruits would require you to identify separate redox titrations specific for glucose and for fructose. Feasibility of the project depends on finding sugar-specific titrations and availability of reagents and equipment at your lab or work area. Researching titration procedures for fructose and glucose would be a good first step for the project.

I hope this helps. Please ask again if you have more questions.

A. Norman

kierracov
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Re: Chemistry Project Topic

Postby kierracov » Tue Jan 15, 2019 1:07 pm

Thank you for your response! After doing some research, I read about determining glucose content through iodometric titration. This is word-for-word a paper I read by A.L. Galant, R.C. Kaufman & J.D. Wilson.

"Early methods for the quantification of glucose relied on its ability to act as a reductant in solution. Although an assortment of metal ions could oxidize the glucose carbonyl group, copper (Cu2+) was the most popular due to the potential for formation of stable precipitates or colorimetric end-products. Benedict’s solu- tion was one of the first widely-used reagents to take advantage of the relevant chemistry, employing sodium carbonate in the presence of copper citrate or tartrate to precipitate Cu2O (Benedict, 1908). This chemistry was co-opted by Otto Folin and Hsien Wu, who coupled the reduction of copper to the oxidation of phosphomolybdic acid (the Folin–Wu method). The result was a blue end-product, which was stable for several days, and which could be compared directly against solutions of known starting sugar content (Folin & Wu, 1919). One short-coming of Benedict’s solution and the Folin–Wu method was the inability to differentiate glucose from other reducing sugars in a complex solution. To address this issue, Cajori devised a method by which excess iodine was first reduced by glucose, and subsequently titrated against thiosulfate to determine the quantity of glucose present. Any fructose and sucrose present would not react with iodine, but fructose that remained after the glucose had been con- verted to gluconic acid could be reacted with copper as previously described by Folin and Wu."

My concern is that it seems like this titration method is not very accurate considering it cannot find glucose and fructose separately. I am confused about the part where it states "To address this issue...fructose remained after the glucose had been converted..." Does this mean that fructose and glucose can be found separately from iodometric titration? Also, I'm unsure if this method is applicable to fruits. Sorry for the long post, chemistry is not my strong suit.

norman40
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Re: Chemistry Project Topic

Postby norman40 » Tue Jan 15, 2019 2:44 pm

Hi kierracov,

Any fruits that you might test contain glucose, fructose and other sugars. Successful analysis of such mixtures requires that you have test procedures that are specific for glucose and fructose. In other words, the test procedure must be able to differentiate glucose and fructose.

The passage you posted briefly describes tests that can differentiate glucose and fructose. The glucose-specific test involves reaction with iodine and titration against thiosulfate and the fructose-specific test involves reaction with copper. These two tests work for sugar mixtures because glucose reacts with iodine but fructose does not.

I hope this helps. Please ask again if you have more questions.

A. Norman

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Re: Chemistry Project Topic

Postby kierracov » Wed Jan 16, 2019 1:24 pm

Hmm...I'm worried that doing glucose and fructose titration might be a little too complicated for my skill level because the two need to be separated. My teacher recommended determining vitamin C content in different fruits using titration, so I would like to do something along those lines. I don't want to do vitamin C particularly since it's very common. However, when I researched titration with fruits, the only thing I could find was vitamin C. Do you know of any other compounds that are present in fruits that I could find with titration? Thank you for your help once again!

norman40
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Re: Chemistry Project Topic

Postby norman40 » Wed Jan 16, 2019 2:47 pm

Hi kierracov,

You could test juices for titratable acidity. In this kind of experiment, the titration doesn't differentiate the different acids that may be present in juice. Rather, the measurement indicates the total amount of acid in the juice.

I hope this helps. Please ask again if you have more questions.

A. Norman

kierracov
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Re: Chemistry Project Topic

Postby kierracov » Wed Jan 16, 2019 6:21 pm

Interesting! To put a twist on that, would the following make for a good experiment:
Determining and comparing the effect of fermentation on either vitamin C content OR titrable acidity in various fruits (e.g. orange, apple, grapes, banana, apricot)

Essentially, I would be just be doing redox titration to determine the vitamin C content for each fruit, but would do the same for the fermented version of each fruit to see it provides higher vitamin C content and thus, more health benefits.

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Re: Chemistry Project Topic

Postby norman40 » Thu Jan 17, 2019 4:14 pm

Hi kierracov,

Investigation of the effect of fermentation on vitamin C content of fruit juices could be an interesting project. But there are many kinds of fermentation processes. You might want to find out if there is a fermentation process that can be used to increase or decrease the vitamin C in juice.

I hope this helps. Please ask again if you have more questions.

A. Norman

kierracov
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Re: Chemistry Project Topic

Postby kierracov » Fri Jan 18, 2019 7:35 pm

norman40,

Thank you for your continuous help. My teacher thought the fermentation idea was creative, but too complex and would get into too much biology. I'm now looking at different conditions that affect vitamin c content in fruits or fruit juices (e.g. temperature, storage, cooking etc.) that I could test for my lab. Many of these ideas are common and overdone, so any other ideas would be greatly appreciated. Once again, thank you so much!

norman40
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Re: Chemistry Project Topic

Postby norman40 » Mon Jan 21, 2019 2:16 pm

Hi kierracov,

One experiment that you might try is a comparison of vitamin C in fresh and commercially prepared juices.

There is a Science Buddies project that involves comparing vitamin C contents of fresh and prepared orange juices. You may be able to modify the project to fit with your interests and the background information provided may be useful to you.

https://www.sciencebuddies.org/science- ... -vitamin-c

I hope this helps. Please ask again if you have more questions.

A. Norman

kierracov
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Re: Chemistry Project Topic

Postby kierracov » Wed Jan 23, 2019 2:19 pm

Hi norman40,

I decided to investigate the effect of heat time on vitamin C content in vegetables (red bell peppers & broccoli). I am using the potassium iodate titration method. So my flask will contain: a vegetable sample, potassium iodide, hydrochloric acid and starch indicator. And the burette will contain the potassium iodate solution.

However, I’m wondering how much I need of each solution. The potassium iodate and potassium iodide are provided by my school, but they are in solid form and don’t have a given concentration. The hydrochloric acid is 0.5M, and soluble starch is being used. I’m using 20mL samples of vegetable juice. How do I figure out how much of each solution I need? There’s obviously experiments online with different measurements, but how do I make such measurements proportionate for my lab? And do I need to know the concentration of potassium iodide and potassium iodate to do the experiment? Please let me know ASAP.

Thanks.

norman40
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Re: Chemistry Project Topic

Postby norman40 » Wed Jan 23, 2019 4:27 pm

Hi kierracov,

Vitamin C titration is a common test and there are many procedures available online that include appropriate reagent concentrations. One example is at the following link:

https://www.thoughtco.com/vitamin-c-det ... ion-606322

If you follow the procedure at the above link (or the Science Buddies project from my previous post) you don't need to know the iodide concentration. Instead, you titrate a known vitamin C tablet and use that result to calculate the amount of vitamin C in a juice sample. My suggestion is to make the solution quantities specified in the above link. You should have plenty for your experiments.

I hope this helps. Please ask again if you have more questions.

A. Norman

kierracov
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Re: Chemistry Project Topic

Postby kierracov » Wed Jan 23, 2019 4:49 pm

The link provided seems to be for iodine titration, not iodate which is what I'm doing. I've figured out how to determine how many g of potassium iodate and potassium iodide I need for the lab, but I'm wondering what an appropriate amount is? I will be using the vitamin C tablet and use it to find the content of vitamin C in my vegetable samples. But does the concentration and grams I use of the potassium solutions affect the titration anyway (i.e. does it make it go faster/slower, does it help with colour change)?

norman40
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Re: Chemistry Project Topic

Postby norman40 » Wed Jan 23, 2019 5:19 pm

Hi kierracov,

The concentrations of iodate and vitamin C will affect the volume of iodate solution you use. Higher iodate concentration means you'll add less iodate solution to your juice sample to complete the titration. Lower vitamin C concentration also means you'll add less iodate solution to the juice sample. But you'll want to titrate enough iodate solution to get a good volume reading from your burette at the endpoint – maybe 10-20 mL. Assuming equal accuracies of the standard and unknown sample titrations, the solution concentrations won't affect the final vitamin C result.

I hope this helps. Please ask again if you have more questions.

A. Norman

kierracov
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Re: Chemistry Project Topic

Postby kierracov » Wed Jan 30, 2019 3:07 pm

Hi there.

I changed my procedure from potassium iodate titration to iodine titration as I found the latter to be much easier. The problem is, my school ran out of iodine solution (Iodine concentrated, Lugol), so I need to use J Crows’ 2% Lugol’s iodine solution to perform my vitamin C titration on red peppers and broccoli instead. However, my teacher wants us to write the report as if we used the school’s iodine solution, so the measurements, concentrations and any calculations must correspond with their solution and the values I would have used given that solution.

I’m unsure how to figure out the amount of 2% solution I need so that it is proportional to the amount I would have used given the pure iodine solution. My original plan was to create a 0.03 M iodine solution. Therefore, I was going to:

Take 20mL of iodine solution
Add 646mL of water to it to dilute to 666mL

I figured this out doing the following dilution calculation:
(1M) 0.02L= 0.03M(?L)

How much of the 2% J Crows’ solution do I need to create a 0.03M iodine solution? How much do I need to dilute it to?

Any help ASAP would be greatly appreciated!


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