17 Experiment 11: Sugar in Various Beverages

Ron’s project 15

measuring sugar in various beverages

objective: To determine sugar content in soft drinks

learning points:

1. use a hydrometer device to determine density of aqueous solutions
2. compare sugar content of “standards” to commercial products
3. graph data and apply graph to determine percent sugar in drinks

A hydrometer is a device utilized to measure the specific gravity (or relative density) of liquids; more specifically, it measures the ratio of the density of the liquid compared the density of water.  A hydrometer is usually consists of a cylindrical stem and a bulb weighted with mercury or lead shot to make it float upright. The liquid that is to be tested is poured into a tall container (e.g. a graduated cylinder), and the hydrometer is gently lowered into the liquid until it floats freely. The region in which the surface of the liquid actually touches the stem of the hydrometer is read for numerical measurement. Hydrometers most generally contain a scale inside the stem, in which the specific gravity can be read directly. A variety of scales exist, with the choice made depending on the liquid and the context.

Hydrometers may be calibrated for various different uses (e.g. such as a lactometer for measuring the density (creaminess) of milk or an alcoholmeter for measuring higher levels of alcohol in alcohol spirits). The operation of the hydrometer is based on Archimedes’ principle that states a solid suspended in a fluid will be buoyed up by a force equal to the weight of the fluid displaced by the submerged part of the suspended solid. Therefore, the lower the density of the substance and the farther the hydrometer will sink.

Because the density of a liquid will change with change in temperature, hydrometers can be calibrated for different reference and sample temperatures. Commonly, specific gravity is measured using the density of water at 4ºC (the temperature of maximum density for pure water). However most current hydrometers used in water quality testing are calibrated for a reference temperature of 60º F.  Because specific gravity measures the mass of a liquid over the mass of distilled water, numerical values of specific gravity obtained by hydrometer are without units. Hydrometers come with different scales depending on the characteristics of the liquid the user is measuring. The measurement made with the hydrometer can be used to calculate the salinity of a water sample.

Using a hydrometer is fairly simple. The student must be careful, however, not to break the glass hydrometer or the cylinder if it is also made from glass.

Safety

Use the normal laboratory precautions identified on the safety sheet you signed. Once the sample is in the lab, unused beverage must be flushed down the drain. Any beverage brought into the lab for study can no longer be treated and ingested as a beverage (even if taken out of the lab room)!  As always: return everything to its place, wipe your bench, lock your drawer, and return the key to the key cabinet.

READING THE HYDROMETER

Hydrometers come with different scales depending on the characteristics of the liquid the student is measuring.

To use the hydrometer, follow the general steps below:

1. Fill the glass cylinder with the sample liquid.
2. Place the hydrometer with the bulb end down. It will bob up and down in the liquid.

Be careful so that the sample liquid will not overflow from the cylinder.

3. Be sure to note that the hydrometer is floating freely.
4. Be sure to record the specific gravity to the maximum resolution of the scale.
5. Note that distilled water is generally taken to be a measurement of 1.000

PROCEDURE

1. Obtain the hydrometer and be careful in handling the glass bulb.
2. You will prepare a set of sugar “standards” that have a known amount of sugar contained.
3. Obtain a stock solution of 16 % sugar. Fill one hydrometer with this standard so that the hydrometer is floating freely.  This is the 16 % sugar standard.
4. Prepare a 8 % sugar standard by mixing 80 mL of the stock 16 % solution with

80 mL of distilled water.  Again fill another hydrometer until the bulb is floating freely.

5. Prepare a 4 % sugar standard by mixing 40 mL of the 16 % stock solution with

120 mL of distilled water.  Fill another hydrometer with this standard.

Prepare a 2 % sugar standard by mixing 20 mL of the 16 % stock solution with

140 mL of distilled water.  Fill another hydrometer with this standard.

6. Now prepare as many other hydrometers with the test beverages/soft drinks designated by the instructor.
7. Read and record all the hydrometers of all prepared mixtures as directed above.

Standards:

Test Beverages/soft drinks:

GRAPHING OF STANDARDS:

1. You will plot on graph paer (or use of EXCEL or QUATTRO PRO) the data obtained from the “standards” and use the graph to estimate the percent of sugar in the soft drinks.
2. On the x-axis plot the numerical values of the percent sugar for each of the four standards. Remember to space the values correctly relative to each other and place a label (Percent Sugar) and units (Percent) on the x-axis.
3. For the y-axis you will plot the specific gravity of the four standards and space the numerical values such that you use most of the graph paper of graphing space. Place the label “specific gravity” for the y-axis, but remember that this measure does not have units.
4. Plot the points correctly and draw the best straight line through the points (if you use EXCEL or QUATTRO PRO the program will draw the line for you if you select “trend line”).
5. You can determine the percent sugar in the test soft drinks by first finding their specific gravity on the y-axis then tracking over to the straight line and downward to the x-axis. The intercept on the x-axis is the percent sugar for that particular soft drink.

Alternatively, you can determine the slope of the straight line by selecting two points on the line (well away from each other) and calculate slope.

Slope =   ΔY/ΔX  =   (Y2 –Y1)/(X2-X1) =   ____________

Now read the y-axis for the y-axis intercep (where the line intercepts the y-axis).

Now you can formulate the equation of the line (m is slope, b is y-axis intercept):

Y  =   mX    +    b

Y  =  _________ X     +       _______

Determine the x-axis value for each corresponding y-axis specific gravity of soft drink.

Record your results in a table and answer the designated questions.

REPORT SHEET                 Name_________

1. Table of percent sugar from standards and test soft drinks

1. Questions
2. Was the “standard” line very close to the actual data points on the graph?
3. Was the standards data highly, moderately, or barely linear?
4. What soft drink had the highest percentage of sugar?
5. What soft drink had the lowest percentage of sugar?
6. Arrange the names of the soft drinks in order from highest sugar content to lowest sugar content?
7. What does your data claim about soft drinks?