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Author Topic: How can the sugar concentration in a solution be measured?  (Read 30568 times)

Offline thegers91

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Hi there,

I am having trouble in deciding what technique(s) I could use for my chemistry project in School. My Project is - Researching and comparing the sugar content of cola, diet coke and perhaps coke zero.

I believe this could potentially be a very interesting project, however, I am struggling to decide the best technique(s) to use. Perhaps a titration? I'm not sure.

Any help and advice would be greatly appreciated  :)

thanks
« Last Edit: 13/10/2008 12:10:18 by chris »


 

Offline RD

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Perhaps compare the sugar content of different brands of non-diet soft drinks
e.g. coca-cola, supermarket "own-brand" colas, Dr Pepper, etc

I think the "diet","one-cal" and "zero" drinks do not actually contain sugar, although you may wish to check this.
I suspect the supermarket "own brand" colas have more sugar than premium brands.
« Last Edit: 16/09/2008 17:23:39 by RD »
 

Offline Bored chemist

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Measuring sugar isn't that easy by titration.
Density measurements or the rotation of the plane of polarised light might be workable as a school experiment.
Also, as RD pointed out, all the "diet" versions have so little sugar it would be hard to measure without rather better equipment.
It's not impossible but the best I can think of is to oxidise any viitamin C with some suitable enzyme (or just ignore it- probably not a problem for some drinks)
Thenm boil the stuff with sulphuric acid to hydrolyse any sucrose to glucose then add alkali then add Fehling's solution and boil it . The glucose reacts with Fehling's solution to give Cu2O which you can filter off and weigh.
Not my idea of a nice practical.
 

Offline RD

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What about using the indicator strips for measuring glucoseuria in diabetics ?

http://www2.shopping.com/xPO-Diastix_Reagent_Strips_for_Urinalysis_To_Test_Urine_Glucose_100_Each  ($15 for 100 test strips)

It would be necessary to dilute the drinks with water until the sugar level was within the test range of the urinalysis test strips.
From the extent of the dilution necessary for each brand of cola it could be possible to accurately measure their relative sugar levels,
 and estimate the acutal quantity of sugar in each brand.
« Last Edit: 16/09/2008 20:30:06 by RD »
 

Offline thegers91

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thanks for the help guys.

really insightful  :)
 

Offline RD

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The diabetic urinalysis test strips use colour change:
the colour of the test strip is compared with a colour chart after a specified time, (typically 45 seconds).

Quote
TESTING TECHNIQUES. Urine samples are tested with a variety of different instruments and techniques.
Some tests use dipsticks, which are thin strips of plastic that change color in the presence of specific substances.
Dipsticks can be used to measure the acidity of the urine (its pH) or the presence of blood, protein, sugar
http://www.answers.com/topic/urinalysis
 

Offline Bored chemist

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I suspect that those strips only respond to glucose and are "blind" to sucrose.
Having said that, boiling the drink with dilute sulphuric acid for a while, neutralising it and then measuring the glucose formed by the hydrolysis of the sucrose might work.
You would need to do a test with known solutions of sugar in water.
I'd be looking really hard at a density measurement- perhaps with a titration to measure the acidity and then correcting for that.
 

Offline thegers91

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this is really great help keep it coming :)

thanks a lot bored chemist and rd!

Ill look into your suggestions and get back to you to tell you how progress is going  ;D


thegers
 

Offline RD

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I suspect that those strips only respond to glucose and are "blind" to sucrose.
Having said that, boiling the drink with dilute sulphuric acid for a while, neutralising it and then measuring the glucose formed by the hydrolysis of the sucrose might work.
You would need to do a test with known solutions of sugar in water.
I'd be looking really hard at a density measurement- perhaps with a titration to measure the acidity and then correcting for that.

Yes BC is correct: these urinalysis tests are "blind" to sucrose,
(if the drinks are only sweetened with glucose then this blindness is not a problem).

There are enzymes which will hydrolyse sucrose into glucose...
 
Quote
Sucrose itself is a non-reducing sugar, having the reducing aldehyde group involved in the glycosidic bond, and therefore will not test positive with Benedict's solution.
In order to test for sucrose, the enzyme sucrase is mixed with the sample. The sucrose is hydrolysed into glucose and fructose, with glucose being a reducing sugar, which will test positive with Benedict's solution. Fructose can be isomerized to glucose by the addition of NaOH or other strong base.
http://en.wikipedia.org/wiki/Sucrase
« Last Edit: 17/09/2008 22:47:17 by RD »
 

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