# Quantitative Benedict's Solution

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### #1 Alserina

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Posted 21 February 2007 - 03:06 PM

Hi guys. So basically I have this science experiment to design and do to find out how much sugar there is in x (where x = type of food).

I thought of boiling a sample of X with Quantitative Benedict's Solution (QBS), and then I guess if it turned a certain colour it meant there was a certain concentration of reducing sugars in it. I mean, all monosaccharides are reducing sugars, and if I boiled the sample long enough, complex sugars would break down into monosaccharides and be reduced.

Can anyone tell me if my idea, facts and procedure of using the Benedicts solution listed above are correct, and where I may get a sample of the colour chart for QBS, or any other method I could use to find out the % concentration of sugar? I tried Googling and it didn't come out.

### #2 Mercedes Benzene

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Posted 21 February 2007 - 03:33 PM

I've only ever tested for sugars through a Benedict's solution titration. I do not think this will work however, since you are testing for the presence of sugars in food.
Mashed up food would make a difficulat titrant.
Anyway, I have never seen a "color key" for Benedict's solution, so I think that comparing various colors would be a poor approach to his assignment.
I'll do some research for you.

### #3 Mercedes Benzene

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Posted 21 February 2007 - 03:38 PM

I did find this:

The method used in Metrohm’s Food PAC for the determination of the total amount of reducing sugars in foodstuff (e.g. honey) is based on Fehling’s test. The sample is treated with an excess of Cu(II) ions which are reduced to Cu(I) ions by the reducing sugar being present. Potassium iodine is used to reduce the remaining excess Cu(II) ions to Cu(I) releasing iodine. Finally the iodine is titrated with thiosulfate solution.

### #4 Alserina

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Posted 21 February 2007 - 04:43 PM

Firstly, thank you =)

May I ask how this titration would work? Like how do I titrate and how I can calculate the amount of sugar based on the amount of stuff I add in to neutralize the solution?

### #5 Mercedes Benzene

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Posted 21 February 2007 - 05:05 PM

Firstly, thank you =)

May I ask how this titration would work? Like how do I titrate and how I can calculate the amount of sugar based on the amount of stuff I add in to neutralize the solution?

Firstly, no problem.

Using just the Benedict's solution (not the method explained by the quote in my second post), you could do a rough estimation of the total amount of sugars in your sample by doing the following:
Use various stock solutions (1, 3, 5, 10, etc %) of glucose. Boil with the Benedict's solution to get an idea of the color change that results from each concentration of glucose.
You could then go in, and slowly titrate each sample of food until you create a color that is most similar to one of your "stock solutions". This will provide an approximate amount of sugar (%), which could easily be converted to mass or any other measurement you need.

The second method that I provided (in the quote) I am not familiar with, however it appears that you could:
Perform an Iodine-Thiosulfate titration and go in reverse stoichiometrically to determine the original amount of sugar present using Iodine -> Copper -> Suger.

As I mentioned earlier, the only downside to this is that you will be using food products, which would make the solutions murky and would disallow the use of Benedict's solution's color changes. If you use food products that are relatively clear, or that could be diluted (like milk or honey), I do not see any reason why a titration would not work.
Best of luck to you!

### #6 Alserina

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Posted 22 February 2007 - 03:21 PM

Perform an Iodine-Thiosulfate titration and go in reverse stoichiometrically to determine the original amount of sugar present using Iodine -> Copper -> Sugar.

Thanks. This titration sounds really complicated, although I'm not sure how we (lab partner and I, we're in high school) can work a titration. By the way, our food sample will be solid, I think it is bubble gum.

The only method of titrating we know of is the one used for acid-base titration, and I am skeptical that we can use the Benedict's quantitative reagent, already boiled with our food as the analyte, and then use the burette to drip in say, 1% glucose concentration, then see how much of that was needed to turn our boiled BQS sample to ph 7, because it doesn't make sense.

So how do we work this Iodine-Thiosulfate titration?

### #7 Mercedes Benzene

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Posted 23 February 2007 - 03:11 PM

Thanks. This titration sounds really complicated, although I'm not sure how we (lab partner and I, we're in high school) can work a titration. By the way, our food sample will be solid, I think it is bubble gum.

I think you misundertood. The titration is not very complicated. It's not an acid-base titration, it's just dripping benedict's solution into a glucose solution in order to compare relative sugar concentrations.

### #8 BobMcG

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Posted 10 October 2009 - 09:27 AM

I have just done this in CHEM365 lab. If you are still interested I can give you details.

### #9 laki14

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Posted 09 December 2009 - 08:03 AM

Please show me the way to calculate the amount of glucose present in the sample, with respect to the standard glucose solution. How do you derive the formula for the calculation?

### #10 laki14

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Posted 09 December 2009 - 08:05 AM

I have just done this in CHEM365 lab. If you are still interested I can give you details.

Please show me the way to calculate the amount of glucose present in the sample, with respect to the standard glucose solution.( any value will do) How do you derive the formula for the calculation?