Science Buddies: "Ask an Expert"

My daughter in 5th grade is doing a project on how much sugar in sodas and juices. Is there a way to actually demostrate or test how much sugar in each beverage beside looking at the nutrition label on the can?

Hi

I have used following website procedure for determining sugar in soda and juices earlier. Choose any of them for quantitative analysis of sugar in beverage drinks.

http://www.netl.doe.gov/coolscience/res ... a_656.html

I'm posting message again regarding the previous link given does not navigate to correct site needed for answering the question.

Please use following link to retrieve info given earlier.

http://www.vrd.org/locator/sites/CoolScience.shtml

Thanks,

I'm reposting the info on the link given earlier for this post. The link has been removed from the given source.

Please refer to the following information.

Q656 – chemistry



On 2/13/01 Funk51563 asked:



I am 9 years old, and a student doing my science project. How can I test sugar in soft drinks?



And Researcher answered:



The major ingredients in soft drinks are water and sugar. The remaining ingredients (flavorings and preservatives) are present in very small quantities. The following methods will work for “clear� liquids such as flat soda pop, apple juice, grape juice, etc. Juices that contain solids (orange juice, tomato juice) will have to be filtered carefully, and may not work.



Several methods could be used.



Method 1:

The sugar content of the soft drink can be reasonably estimate by understanding density. Water has a density of 1.00 g/ml. The addition of the sugar is assumed to be negligible in terms of the effect on the final volume of the solution.



Required materials: A method for measuring a precise volume and an analytical balance.



Example: 10 ml of “flat� soda pop is placed in a volumetric flask weighing 100grams. The soft drink and flask together weigh 111.1 grams (its density therefore is 1.11g/ml). The soft drink weighs 11.1 grams. If the weight of the water in 10 ml of soda pop is 10g, then the weight of the sugar in 10ml of soda pop is 1.1 grams.



A 12-oz can of soda pop has 355ml of soda pop. Solving a simple algebraic equation where x is the weight of sugar in a 355 ml (12 oz) can of soda pop:



X = 1.1 then 10X = 394.05; X=39.4 grams sugar

355 10.0





An alternative method using density and a preparing a calibration curve can be found at:

http://wwwchem.csustan.edu/CHEM1102H/howsweet.htm



Method 2:

Take any soft drink and place in a tared (pre-weighed) container that you can heat (on the stove, microwave, or Bunsen burner, for example). Pour a known quantity of soft drink into the container and carefully boil away the water leaving behind the sugar. Be careful as the container approaches dryness. When the residue is completely dry and cool (and hopefully not burned), re-weigh the container and determine how much sugar (by difference) was in the volume of liquid.



Method 3:

Refractometers are simple optical instruments for measuring the amount that a pure liquid or transparent solution bends light. The amount of bending is determined by the chemical nature of the liquid, or in case of sugared waters, the amount of sugar dissolved on the water. Various refractometers are made for measuring the dissolved solids content of liquids from fruits, grasses, vegetables, etc. Vintners, for example use them to determine the quality and timing of the grape harvest. Commercial refractometers designed for measuring sugar content measure in % sucrose by weight (Brix©) can be calibrated with distilled water and/ or with a sugar standard solution. Refractometers should be available from stores that sell winemaking supplies, or from scientific catalogs.



You may be able to find Brix refractometers for sale on the World Wide Web.



A science project might involve comparing the three methods of determining sugar content.

There is another optical method to determine the amount of sugar in a clear liquid using polarized light. Sugar is a chiral molecule. It rotates the polarization of light as it passes through it.

Try this experiment, take two pieces of polarizer material. Two pairs of Polaroid brand sunglasses may work fine. Place a sample of the water with sugar in a large clear glass container inbetween the two pieces of polarizer sheets or glasses and observe a light source through the sandwich. You should notice that the amount of light changes with the distance that the light much travel through the glass. Now rotate the polarizer sheet with respect to each other... the place that is the darkest will shift. You may also see some nice color variation as well. The effect is stronger with more sugar in the water.

The effect is caused by the light being polarized as it passes through the first polarizer, then being rotated by the sugar in the water, then being "analyzed" by the second polarizer. If no sugar is present, the two polarizers may be crossed, so that no light may get through at all... then in the presence of sugar, the light will be rotated by some amount, allowing light to pass through the second polarizer.

For measurements, one must have a method of calibrating the system such that one can determine how much sugar leads to how much polarization rotation effect.

Here are a few links on this subject:

http://sgc.engin.umich.edu/kids/polarizedlight.shtml

http://www.exploratorium.edu/snacks/rotating_light.html

http://www.fas.harvard.edu/~scdiroff/ld ... yrups.html

http://organic.utep.edu/polar/demosbackup.htm

Here is an interesting link to a bit of science history on this very topic, and how this property was used to measure sugar concentration during the mid-19th Century:

http://museum.nist.gov/panels/bates/improve.htm

Good Luck