Larry’s Lost Labels Luncheonette

Introduction

Welcome to Larry’s Luncheonette, located on Flinn Street in Sciencetown. Flinn Street is a very busy street in Sciencetown and Larry’s Luncheonette sees many patrons each day. This little café serves up some of the best blue plate specials as well as an extensive selection of world-famous breads and pastries. Unfortunately, Larry’s Luncheonette is closed down due to a prank. The labels were removed from some of the containers in the kitchen. Help Larry identify the contents of the containers and allow him to reopen the luncheonette.

Concepts

• Chemical reactions
• Acids and bases
• Melting point
• Solubility
• Density

Background

Larry uses many different ingredients in his culinary creations. As a prank, Mark Mischievous, one of Larry’s new employees, removed labels from many of the containers in Larry’s kitchen. The containers were not opened so there is no chance that the substances were mixed with one another; however, all the containers look alike. In order to save the luncheonette from staying closed to restock and losing vast amounts of revenue, Larry is asking for your help to identify the contents of the containers that are missing labels.

Larry stores salt, baking soda, flour, corn starch and sugar in large identical containers. Luckily, the label was not removed from the flour, which Larry used in many of his baked goods. The labels from the sugar, salt, baking soda, and corn starch were removed. He also has containers of water and vinegar. The labels on both of these products were also removed.

Larry uses corn starch to thicken his sauces and will not be able to make his world-famous gravy for the mashed potatoes on today’s blue-plate special without it. Salt is used to season many dishes and is one of the ingredients used in his delicious breads. In addition, the breads he makes would not rise without the aid of baking soda. Vinegar is used as a salad dressing. Larry serves the bottled water to his patrons, instead of the Sciencetown tap water. Finally, powdered sugar is one of Larry’s favorite garnishes. He sprinkles it on top of many of his pastries and cakes. Larry is lost without knowing the identity of each ingredient in his kitchen. Can you imagine how it would affect his business if corn starch were sprinkled over his pastries or salt were used to thicken the gravy? He would inevitably receive complaints and possibly lose customers.

Some very simple tests can be employed to help Larry recover from this fiasco.

• Iodine can be used to identify which of his ingredients is a starch. A few drops of iodine on sugar, salt or baking soda will not produce a color change from iodine’s already red-brown color; however, when exposed to the corn starch the iodine will produce a blue-black color.
• Vinegar can be used to identify the baking soda and vice versa. This acidic liquid will quickly react with baking soda, a base, to produce carbon dioxide gas. The solid that foams when vinegar is added must be baking soda; conversely, the liquid that forms when baking soda is added must be vinegar.
• Due to the polar nature of water, salt will quickly dissolve to form an ionic solution. Therefore, the substance with the highest rate of solubility must be salt.
• Sugar has the lowest melting point of the other unlabeled substances. Upon heating, sugar will be the first substance to melt.

As a scientist, your skills are needed to help Larry re-label his containers. Samples of each substance should be tested and the results recorded on your observation sheet to send to Larry so he can replace the labels and open for business.

Materials

Safety Precautions

Use only borosilicate glass (e.g., Pyrex^®) when heating on a hot plate. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

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. Iodine starch solution may be disposed of according to Flinn Suggested Disposal Method #12a. Vinegar may be disposed of according to Flinn Suggested Disposal Method #26b. Corn starch, baking soda, salt and sugar may be disposed of according to Flinn Suggested Disposal Method #26b.

Prelab Preparation

1. Using a spatula, weigh out approximately 7 g of each solid in a weighing dish labeled with the following sample letters:

A—Baking soda
B—Corn starch
C—Salt
D—Sugar 

2. Using a 25-mL graduated cylinder, separately measure approximately 10 mL of water and vinegar and place in beakers with the following sample letters:

E—Water
F—Vinegar

Procedure

1. Read the background section to the class to set up the scenario.
2. Using a spatula, place approximately 2 g of each solid in separate large test tubes. Label the test tubes.
3. Pour approximately 2 mL of vinegar in each of the four large test tubes and observe for a reaction which produces gas and bubbles. The solid that reacts is baking soda. Record observations in the data table.
4. Obtain four clean, large test tubes or rinse and dry the test tubes.
5. Using a spatula, again place approximately 2 g of each solid in separate large test tubes. Label the test tubes.
6. Add approximately 1 mL (24 drops) of iodine starch indicator to each of the four large test tubes and observe for a blue-black color change. The solid that turns blue-black is corn starch. Record observations in the data table.
7. Obtain four clean, large test tubes or rinse and dry the test tubes.
8. Using a spatula, again place approximately 2 g of each solid in separate large test tubes. Label the test tubes.
9. Pour approximately 2 mL of water in each of the four test tubes and observe which solid dissolves first. The solid that dissolves first is salt. Record observations in the data table.
10. Using a marker, label four sections of a watch glass A, B, C and D.
11. Using a spatula, place approximately 1 g of each solid in separate piles on the appropriately labeled sections of the watch glass.
12. Place the watch glass on a hot plate and heat. Observe which solid melts first; this should take one to two minutes. The solid that melts first is sugar. Record the results in the data table.
13. Obtain two clean, large test tubes or wash and dry the test tubes.
14. Pour 5 mL of each sample into a separate large test tube. Label the test tubes.
15. Using a spatula, place approximately 2 g of baking soda into each test tube and observe for a reaction that produces gas and bubbles. The liquid that reacts is vinegar and the other liquid is water. Record observations in the data table.

Student Worksheet PDF

12774_Student1.pdf

Teacher Tips

• This kit contains enough chemicals to perform the demonstration seven times.
• Be creative—add to the given scenario or write an additional scenario that is appropriate for your class.
• Due to the flat bottom, a Pyrex^® Petri dish may be more efficient on the hot plate than the watch glass.
• Remind students that, just like the Diner, the laboratory cannot operate with mystery substances. Labels are very important and Flinn recommends that you and your students become label fanatics. Remind students that labels should be affixed as permanently as possible and to use inks that the substance in the container will not affect. They should never use substances from unlabeled containers or place labels on top of each other. A consistent labeling system makes proper storage and maintenance of your chemical inventory much easier.
• Refer to the article, The Dos and Don’ts of Chemical Labeling, in your current Flinn Scientific Catalog/Reference Manual for labeling requirements.
• Excellent chemical labeling software is available from Flinn Scientific (Flinn Chemical Labeling Software, Catalog No. SE2553).

Sample Data

Answers to Questions

1. Why is it important to properly label all substances in the science laboratory?
   

   Student answers will vary but should include that an unlabeled bottle becomes a mystery substance that could be dangerous.

2. Are there any other ways, besides tasting, that would have also allowed you to determine the identity of an unknown substance?
   

   Student answers will vary but may include texture, odor, color, particle size, microscopic properties, reactivity, conductivity or flammability; accept all reasonable answers.