How Sweet It Is—How Much Sugar Is Really in That Soda?
AbstractYou know there is sugar in non-diet soda, but just how much sugar? Sure, you can look on the ingredients label, but how do food scientists actually measure the amount of sugar in a solution? They use a simple scientific device called a hydrometer. The hydrometer floats in the solution that is being tested, and the higher it floats, the more sugar there is! In this science fair project, you will use a precision hydrometer to measure the amount of sugar in soda.
David B. Whyte, PhD, Science Buddies
Use a hydrometer to measure the amount of sugar in soda.
Figure 1. A hydrometer immersed in liquid inside a graduated cylinder. The density of the liquid can be read from the scale inside the hydrometer at the surface of the water. (Wikipedia, 2009.)
How much salt is in seawater? How much blue dye is in that fruit drink? Or how much sugar is in your can of soda? Chemists have many ways to measure the concentration of various substances in solutions. To measure the amount of salt in seawater, for instance, they might measure how well the solution conducts electricity, since the higher the level of dissolved salt, the higher the electrical conductivity of the water. Or to measure how much blue dye is in a blue-colored solution, they might measure how much light is absorbed by the solution, since the more blue dye there is, the less light will pass through the solution. And one way to measure the amount of sugar in a solution is to determine its density (the mass per unit of volume). The higher the density, the higher the concentration of sugar. Pure water at room temperature has a mass of 1 gram (g) per 1 cubic centimeter (cm3), or a density of 1.0 g/cm3. For comparison, lead has a density of 11.4 g/cm 3. So if you had equal volumes of lead and water, the lead would weigh over 11 times as much as the water! Scientists have studied how the density of a solution changes as the amount of sugar increases. Based on this data, if you know the density of a sugar solution, you can look up the concentration of sugar. The density can be measured easily, using a hydrometer, shown to the right in Figure 1.
A hydrometer is made of glass and consists of a cylindrical stem and a bulb weighted with lead, or other heavy metal, to make it float upright. The hydrometer is gently lowered into the liquid to be tested until it floats freely. The point at which the surface of the liquid touches the stem of the hydrometer depends on the density of the solution. The hydrometer contains a paper scale inside the stem, so that the density can be read directly.
The operation of the hydrometer is based on Archimedes' principle, which states that a solid suspended in a liquid will be buoyed up by a force equal to the weight of the liquid displaced. In other words, the denser the solution, the higher up the hydrometer will float. The scale on the hydrometer goes from 0 to 70. This is the percent of sugar. So for water, the hydrometer sinks down to the region where the scale says "0" at the level of the liquid surface, since there is no sugar in water (the solution). In a 30-percent sugar solution (30 g of sugar in 100 g of solution), the hydrometer floats so the number 30 is at the surface of the solution. The food industry refers to the percent sugar as degrees Brix, (°Bx) so a 30-percent solution is 30 degrees Brix, or 30°Bx.
Sugar is a key ingredient in soda, and in many more of our favorite foods and drinks. It provides the sweetness that makes the soda so appealing, yet is also full of unnecessary calories. If you drink non-diet sodas, you know they are usually sweet, but do you know how sweet? How many spoonfuls of sugar are there in a single can of soda? In this food science fair project, you will use a hydrometer to determine the amount of sugar in your favorite soda. See if your experiments confirm the sugar content on the label!
Terms and Concepts
- Archimedes' principle
- Degrees Brix (°Bx)
- Standard solution
- Standard curve
- Why do some businesses use hydrometers?
- How does a hydrometer work?
- What is the definition of solution?
- Can you explain Archimedes' principle in your own words?
- Wikipedia Contributors. (2009, May 15). Hydrometer. Retrieved May 21, 2009.
- Avogadro's Lab Supply, Inc. (2012). How To Use A Hydrometer. Retrieved January 30, 2012.
For help creating graphs, try this website:
- National Center for Education Statistics. (n.d.). Create a Graph. Retrieved May 21, 2009.
Materials and Equipment
- Hydrometer, 0–35° Bx, available at kitchen specialty stores and online from Amazon.com
- Measuring container, 2-liter (L)
- Non-diet soda, 2-L plastic bottle (1)
- Funnel; available at kitchen stores and online from Amazon.com
- Plastic bottles, 2-L, empty and with caps (6)
- Masking tape
- Permanent marker
- Lab notebook
- Sugar (sucrose), pure, white, granulated (5 pounds)
- Kitchen scale, such as the Fast Weigh MS-500-BLK Digital Pocket Scale, 500 by 0.1 G, available from Amazon.com
- Tap water; distilled, de-ionized water is preferable, but for this procedure, tap water is fine.
- Graph paper
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Important Notes Before You Begin:
- The Brix scale actually measures the total dissolved solids. For soda, almost all of the dissolved solids are sugar, so the hydrometer reading reflects the percent sugar.
- The density change that occurs as more and more sugar is added to a solution depends on the temperature of the solution. The scale inside the hydrometer is for 20°C. For the purposes of this science fair project, you will assume the temperature is 20°C. If you do want to correct for the temperature, a table is provided with the hydrometer that shows you how.
- The procedure calls for using 2-L containers. The reason for using large bottles is that the hydrometer sinks up to 26 cm (10 inches) in the liquid. Other tall containers may be substituted as long as they can accomodate the hydrometer.
Removing Carbon Dioxide from the Soda
- The first step is to remove the carbon dioxide gas in the soda; otherwise, the bubbles from the carbonated drink will stick to the hydrometer and result in an inaccurate reading. Note: If the soda you are using is non-carbonated, skip this section.
- Pour the soda out of its bottle and into the 2-L container.
- Pour the soda back into the bottle, using the funnel if needed.
- Repeat pouring back and forth five times, or until there are no more carbon dioxide bubbles being produced.
- Pour the soda into the bottle.
- Leave the lid off to let any remaining gas escape.
- The contents should be at room temperature when you measure the sugar content.
Creating the Sugar Solutions
- The next step is to make a series of standard solutions. This is a series of solutions with increasing amounts of sugar. You will use the data for the density of these solutions to make a standard curve, which is a method to plot your data that will show the concentration of a substance.
- Label the six empty 2-L containers with masking tape and the permanent marker, as follows:
- 0% sugar
- 5% sugar
- 10% sugar
- 15% sugar
- 20% sugar
- 25% sugar
- Weigh out 100 grams (g) of sugar on the kitchen scale and put it into the bottle labeled "5% sugar." Use the funnel, if needed. This will be a 5 percent solution of sugar in water.
- Weigh out the following amounts of sugar and pour it into the corresponding container:
- 10% sugar bottle: 200 g of sugar
- 15% sugar bottle: 300 g of sugar
- 20% sugar bottle: 400 g of sugar
- 25% sugar bottle: 500 g of sugar
- Add water to each 2-L bottle (0%–25%) up to 2,000 mL (2 L).
- Leave about 3 cm of air below the screw cap to allow for the volume increase when the hydrometer is immersed in the solutions.
- All of the bottles should have the same volume when filled.
- Put the caps on the bottles and shake to mix them, until all of the sugar is dissolved.
Testing the Sugar Solutions
- All of the solutions should be the same temperature before testing. Place the hydrometer in the "0% sugar" bottle or sediment tube. Immerse the hydrometer gently to avoid breaking the glass bulb.
- Record the hydrometer reading in your lab notebook.
- Note: You need to be able to read the value on the hydrometer at the surface of the liquid. It is easiest to read the hydrometer when the water is slightly below the top of the bottle (involves some overflowing) or the surface of the water is below the cylinder where the cap screws on.
- Experiment to see what works best for you.
- Repeat the hydrometer reading for the 5%, 10%, 15%, 20%, and 25% sugar bottles.
- Rinse and dry the hydrometer between readings.
- Record the hydrometer readings in your lab notebook.
- Repeat steps 2–4 two more times. This will allow you to obtain more-accurate data.
Testing the Soda
- Place the hydrometer in the soda.
- Record the value on the hydrometer scale in your lab notebook.
- Remove the hydrometer, and rinse and dry it.
- Repeat steps 1–3 for the soda two more times.
Graphing Your Results
- Graph the data for your standard curve, with the percent sugar on the x-axis and the hydrometer reading on the y-axis. You can use graph paper, or a website like Create a Graph. Graph each point separately, or use the average values.
- Determine the sugar content of the soda by looking at the standard curve.
- Find the value for the hydrometer reading on the y-axis, and then find the corresponding value for the sugar concentration on the x-axis.
- Suggestion for your presentation: Put out a bowl with the amount of sugar you determined that is in the soda bottle, along with the soda bottle. See if people think it looks like more or less than they would have guessed.
Ask an Expert
- One possible source of error for this science project is the fact that many sodas are made with fructose rather than sucrose (sugar). Modify the procedure to use corn syrup (fructose) rather than sugar. Do you get the same or different results? How do the hydrometer readings compare for the sugar solutions versus the corn syrup solutions?
- Test other sugar-containing drinks, such as grape juice, apple cider, sports drinks, etc.
- Add yeast to a sugar solution or natural juice (without preservatives) and use the hydrometer to track the decrease in sugar concentration due to fermentation.
- Make a standard curve for sodium chloride at 0, 1%, 2%, 3%, and 5% and use it to determine the amount of salt in seawater. You can purchase "instant sea water" at any pet store that has saltwater aquarium supplies. (This will be more challenging than the sugar experiment because of the lower concentrations.)
- Make your own hydrometer and compare its accuracy to the precision glass hydrometer.
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