General, Organic and Biological Chemistry Kit
Materials Included In Kit
Food coloring (red, blue and yellow), 15 mL each*
Sucrose, 500 g*
Gatorade®, Fruit Punch
Pipets, 10-mL, 12
*See Prelab Preparation.
Additional Materials Required
Water, distilled or deionized
Balances, electronic, 0.01-g precision, 3–5 (may be shared)
Additional beverages to be tested†
Beakers, 100-mL, 12
Erlenmeyer flasks, 125-mL (or other rinse containers), 12
Pipet bulbs or pipet fillers, 12
†See Lab Hints.
Prepare the following reference solutions by placing the ingredients in a suitable container, such as a large beaker, Erlenmeyer flask or bottle. Stir or shake well until all of the sugar has dissolved and the solutions are homogeneous.
- 0% sugar: 500 g of distilled or deionized water
- 5% sugar: 475 g of water, 25 g of table sugar and two drops of yellow food coloring
- 10% sugar: 450 g of water, 50 g of table sugar, one drop of blue and one drop of yellow food coloring
- 15% sugar: 425 g of water, 75 g of table sugar and two drops of blue food coloring
- 20% sugar: 400 g of water, 100 g of table sugar and one drop of blue plus one drop of red food coloring.
Although the materials in this experiment are considered nonhazardous, please follow all normal laboratory safety guidelines. Wear chemical splash goggles whenever working with chemicals, heat or glassware in the lab. Food-grade items that have been brought into the lab are considered laboratory chemicals and are for laboratory use only. Do not taste or ingest any materials in the chemistry laboratory.
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. All solutions may be rinsed down the drain with plenty of water according to Flinn Suggested Disposal Method #26b.
- The experimental work for this lab can be completed within a typical 2-hour lab period. This experiment can also be downscaled to a 2-mL scale using plastic disposable syringes or disposable pipets.
- Juices and sports drinks such as Gatorade® can be used as is from the bottle. Carbonated beverages must be “flattened” first to remove the gas bubbles. This can be done by pouring the beverage back and forth between two large containers. Carbonated gas or air bubbles will interfere with the accuracy of the volume measurement. Juices containing a large amount of pulp should also be filtered before use.
- Review with students the correct use of a pipet and how to read a meniscus. Students should be encouraged to work in pairs, but do not allow one student in a pair to become the professional data recorder. Each student should learn and practice the correct pipetting techniques.
- Volumetric pipets provide the most accurate and precise volume transfer. If these are not available, Mohr pipets or inexpensive, disposable serological pipets may also be used.
- Consider investing in pipet fillers to replace pipet bulbs. Pipet fillers are much easier for students to use.
- This experiment gives excellent results. Choose beverages whose sugar contents are relatively far apart (more than 1 g of sugar per serving size). See the Sample Data results table for examples.
- The “exception that proves the rule” in this study is Powerade (and other types of sports drinks). The working assumption in this experiment is that sugar is the main ingredient whose concentration contributes to the density of the solution—the other ingredients should not be present in large enough amounts to affect the density. This assumption is true for sodas and juices, but not for sports drinks, which contain large amounts of salts (particularly sodium and potassium chloride) to maintain electrolyte balance. Sports drinks thus provide a good example to stimulate classroom discussion of the experiment and its underlying assumptions.
- Fructose (“fruit sugar”) is the main sugar present in fruit juices, fruit drinks, such as Snapple®, and carbonated sodas. In fact, “high fructose corn syrup” is usually the second ingredient (after water!) listed on the ingredients label. Table sugar is sucrose, a disaccharide composed of one molecule of fructose combined with one molecule of glucose.
- We tested fructose and sucrose reference solutions in this lab to see which one gave better agreement with the information provided on the nutrition labels. Both fructose and sucrose gave excellent graphs of density versus percent sugar concentration. Percent sugar concentrations were calculated for all of the beverages using both sets of data (fructose and sucrose). Both sets of results agreed equally well with the nutrition label information—there was no difference in the accuracy (percent error) of these two methods. For this reason, the experimental section for this lab was written using the more readily available “table sugar” (sucrose) rather than fructose.
- Students may be confused about how to read a nutrition label. Consider the sample label shown here. The relevant information on this label is the grams of sugars, not the Percent Daily Value. This soda contains 40 g of sugar per 355 mL of beverage.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering Practices
Asking questions and defining problems
Planning and carrying out investigations
Analyzing and interpreting data
Using mathematics and computational thinking
Engaging in argument from evidence
Obtaining, evaluation, and communicating information
Disciplinary Core Ideas
MS-PS1.A: Structure and Properties of Matter
HS-PS1.A: Structure and Properties of Matter
Scale, proportion, and quantity
MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
HS-PS1-1. Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.
Answers to Prelab Questions
- If the following mass and volume data are used to calculate the density of solution, how many significant figures are allowed in the calculated density? Mass of solution = 12.53 g; volume of solution = 8.27 mL.
The number of significant figures allowed in the calculated density is three.
- Calculate the density of the solution described in Question 1.
- According to its nutrition label, orange soda contains 49 g of sugar per 355-mL serving. If the density of the beverage is 1.043 g/mL, what is the percent sugar concentration in orange soda? Hint: This is a 2-step problem. First, use the density to convert the 355-mL serving size to grams. Then, calculate percent sugar in the beverage.
- How well does the sweet taste of a beverage correlate with the amount of sugar it contains? Based on your memory of taste, predict the relative sugar content of the following beverages that will be tested in this lab: cola, grape juice and sports drink.
Student predictions will vary. Remind students not to taste any beverages in the lab.
- The following graph is a calibration curve for the density of an aqueous salt solution versus percent salt concentration. If the density of seawater is 1.025 g/mL, what is the percent salt concentration?
According to the graph, seawater contains 3.8–3.9% salt (sodium chloride).
Answers to Questions
- Plot density versus concentration for the five reference solutions on a graph. The concentration is the independent variable (x-axis), and the density is the dependent variable (y-axis). Use a spreadsheet program or ruler to draw a “best-fit” straight line through the data points.
- Use the graph to estimate the unknown sugar concentration in each beverage. To do this, locate the point on the y-axis that corresponds to the density of the beverage. Follow that point on the y-axis across horizontally to where it meets the best-fit straight line. Read down vertically from this point on the best-fit line to the x-axis to estimate the percent concentration of sugar in the beverage. Construct a results table and record the density of each beverage and its estimated percent sugar concentration.
See the Sample Data results table.
- Calculate the actual or accepted value of the sugar concentration in weight percent for each beverage, using the nutrition label information and the measured density value. Hint: See Prelab Question 3 for how to do this calculation. Record both the nutrition label information and the actual percent sugar concentration in your results table.
Sample calculation for cola:
Nutrition label: 42 g of sugar per serving (355 mL)
Density (determined in this experiment): 1.038 g/mL
See the Sample Data results table.
- Calculate the percent error in your experimental determination of the sugar content in each beverage. Enter the percent error in the results table.
See the Sample Data results table.
- What was your measured density for pure water (0% sugar solution)? The density of water is usually quoted as 1.00 g/mL, but this precise value is for 4 °C. Comment on why your measured density might be higher or lower than 1.00 g/mL.
The measured density of pure water was 0.998 g/mL. This is less than the quoted density of 1.00 g/mL because the temperature was higher than 4 °C.
- This lab looks at the relationship between the density of a beverage solution and its sugar content. What assumption is made concerning the other ingredients in the beverage and their effect on the density of the solution? Do you think this is a valid assumption? Explain.
The assumption in this lab is that sugar is the major ingredient in each beverage. It is further assumed that the other ingredients are present in small enough amounts that they do not affect the beverage density. This assumption is not valid for certain types of beverages, such as sports drinks, that contain other salts in high concentrations.
- When plotting data, such as that obtained in this experiment, why is it not appropriate to “connect the dots?” If you were to repeat the lab, do you think you would get exactly the same results? Comment on sources of error in this experiment and their likely effect on the results.
You cannot “connect the dots” with the data points on the graph because this would “hide” the straight-line relationship through the data. Each point should actually be represented by error bars that define the precision or reproducibility of each measurement. Thus, if a density “point” at 1.032 g/mL were measured again, it might come out 1.029 or 1.036 g/mL. Sources of experimental error include variations in volume transfer using the pipet, contamination of the pipet from one solution to another, the presence of bubbles in carbonated beverages, etc.