Loudoun County Public Schools



SUGAR CONTENT

Density Analysis (30 points)

This lab procedure was adapted from CHEMFAX! Published by Flinn Scientific, Inc.

Purpose

The density of a solution depends on its concentration, that is, how much solute (solid) is dissolved in the solvent (liquid). If the known density of a solution is plotted on a graph against the known concentration of the solute, a regular pattern is evident – density is proportional to concentration. The resulting graph, called a calibration curve, shows a straight-line relationship between the density of a solution and the concentration of the solute. A calibration curve can be used to determine the concentration of solute in an unknown solution whose density has been measured.

The purpose of this lab is to measure the densities of popular beverages and determine the sugar content using a calibration curve obtained by plotting the densities for a series of reference solutions versus percent sugar. The experimentally determined percent sugar for the beverages will be compared against the information provided on their nutritional labels to evaluate the accuracy of the method.

Equipment

Sugared beverages 25 mL graduated cylinder Thermometer Electronic balance 100 mL beakers (2)

Procedure (repeat steps 1 – 12 until all the beverages have been tested)

1. Pour 30.0 mL of beverage into one of the beakers.

2. If the beverage is a soda, pour the beverage from one beaker into the other until the soda is flat. If the beverage is not a soda, skip this step.

3. Measure the temperature of the beverage and record it on the data table.

4. Turn on the electronic balance.

5. Place the empty 25 mL graduated cylinder on the balance and press the “tare” button.

6. Trial 1 - remove the graduated cylinder and fill it to the 10.0 mL mark with the beverage. Record the volume.

7. Trial 1 - return the graduated cylinder and beverage combination to the balance. Measure and record the mass.

8. Calculate and record the density of the solution.

9. Trial 2 - remove the graduated cylinder from the balance and add another 10.0 mL of the beverage to the graduated cylinder from Trial 1. Record this volume.

10. Trial 2 - place the graduated cylinder and beverage combination on the balance. Measure and record the mass.

11. Calculate and record the density of each trial.

12. Determine the average density of the beverage from the two trials.

Data

|Beverage | | | | | |

| | | | | | |

|Temperature (0C) | | | | | |

|Trial 1 | | | | | |

|Volume of beverage | | | | | |

|(mL) | | | | | |

|Trial 1 | | | | | |

|Mass of beverage (g) | | | | | |

|Trial 1 | | | | | |

|Density (g/mL) | | | | | |

|Trial 2 | | | | | |

|Volume of beverage | | | | | |

|(mL) | | | | | |

|Trial 2 | | | | | |

|Mass of beverage (g) | | | | | |

|Trial 2 | | | | | |

|Density (g/mL) | | | | | |

|Average Density | | | | | |

|(g/mL) | | | | | |

NOTE: IF YOU GET A DENSITY THAT IS LESS THAN ONE, THEN YOU NEED TO TAKE YOUR DATA AGAIN AND RE-CALCULATE

Data Analysis (Graph is worth 5 points) – attach a copy to this lab report

1. Use EXCEL to build the calibration curve, plot the known density on the y-axis versus percent sugar on the x-axis for the following reference sugar solutions. Properly label all axes and title the graph. This should be a scatter plot.

|Percent Sugar (%) |Density at 250C (g/mL) |

|0 |1.0000 |

|1 |1.0020 |

|5 |1.0180 |

|10 |1.0381 |

|15 |1.0590 |

|20 |1.0810 |

|30 |1.1270 |

|40 |1.1765 |

|50 |1.2295 |

2. Use the graph to estimate the sugar content in the beverage. RIGHT CLICK on any data point on the graph and click “add trendline”. Pick a “linear” trendline and click “display equation on chart” at the bottom of the dialogue box. This should give you an equation where you can plug in the average density for the y-variable and solve for the x-variable, which is the percent sugar. Record this value in the Results Table.

Example: your density value is 1.038 g/mL so according to the calibration curve the % sugar is 10.0%

3. Consult the nutritional label on the beverage. It should list the sugar content in grams of sugar per serving size. Record this value in the Results Table.

Example: the nutritional label states there are 42.0g of sugar in a 355 mL serving

4. This value can be converted to percent sugar in the beverage by dividing the grams of sugar per serving size by the volume of the serving size (in mL), then dividing this result by the measured density of the beverage and multiplying by 100.

Example: [(42.0 g) ( (355 mL)] ( (1.038 g/mL) x 100 = 11.4%

5. Calculate the percent difference in the experimental determination of the sugar content using the following equation. Percent difference is used when both values mean kind of the same thing. It is the difference between two values divided by the average of the two values. Shown as a percentage:

% difference =

(|% sugar from the equation of the line – % sugar calculated from the can contents| ) x100

(average value % sugar)

Example: % difference = ( |10.0 – 11.4| ( 10.7) x 100 = 13.1%

6. Use the theoretical values of the percent sugar to determine the percent error between it and the % sugar calculated from the equation for the line.

% error = (|calculated value % sugar – theoretical value % sugar|) ÷ (theoretical value % sugar) x 100

Example: (|10.0 – 10.8|) ÷ (10.8) x 100 = 7.41%

Results Table

|Beverage |Dr. Pepper |Root Beer |Mountain Dew |Pepsi | |

| | | | | |Orange |

|Density of the beverage | | | | | |

|(g/mL) | | | | | |

|Serving size (mL) | | | | | |

|Grams of sugar per serving | | | | | |

|% sugar calculated from can| | | | | |

|label | | | | | |

|(5 points) | | | | | |

|% sugar calculated from the| | | | | |

|calibration curve equation | | | | | |

|(5 points) | | | | | |

|% difference | | | | | |

|(5 points) | | | | | |

|Theoretical |10.8 |13.7 |12.0 |10.8 |10.6 |

|% sugar | | | | | |

|% error (5 points) | | | | | |

Questions (Answer using complete sentences)

(2 points) 1. In the procedure, the temperature of the beverage is recorded. Does temperature have an effect on the density of a liquid? If so, what is the effect?

(2 points) 2. This lab examines the relationship between the density of a beverage and its sugar content. What assumption is made concerning the other ingredients in the beverage and their effect on its density?

(2 points) 3. Is this a valid assumption? Why or why not?

(1 point) 4. What did you assume to be the constant in this experiment?

(2 points) 5. List two sources of error that could have occurred in the experiment. (Math errors and human errors are not considered sources of experimental error).

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