Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Determine the number of unknown powders that will be used during this laboratory activity.
2. The unknown powders may be any combination of the four powders included in the kit. One suggested set of unknowns is the following. Another possibility is to assign different unknown numbers to the same mixture.
   {13034_PreLab_Table_1}
3. To prepare any of the unknowns, combine equal amounts of each powder.
4. Keep in mind that each group will need approximately 2 g of each unknown assigned.
5. Place the unknown in a small container.
6. Label the container with the number of the unknown powder.

Safety Precautions

Avoid coming in contact with the iodine starch indicator. It will stain skin and clothing. The iodine starch indicator solution may be irritating to skin and eyes. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. 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 indicator solution may be disposed of according to Flinn Suggested Disposal Method #12a. Vinegar may be disposed of according to Flinn Suggested Disposal Method #26b and corn starch, baking soda, salt and sugar may be disposed of according to Flinn Suggested Disposal Method #26a.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. This laboratory activity can reasonably be completed in one 50-minute class period.
• Consider telling students the number of unknown powders in each sample, especially when using salt as it may be the most difficult for students to distinguish.
• Purchase the store-labeled counterparts of the powders and indicators to provide the students with a visual of each item. Use these items to restock the kit and to provide more materials for additional experiments. This will also reinforce the fact that the students are working with common household items.
• Remind students that food-grade products become chemicals when brought into the science laboratory. Students should not eat or taste any of these items to determine their identity.
• Weighing dishes, well plates, or beakers could be used in lieu of Petri dishes when using indicators.
• A Pyrex^® or Kimex^® beaker or Petri dish could be substituted for the watch glass when heating the powders. Use only borosilicate glassware when heating substances on a hot plate.

Teacher Tips

• This is an excellent activity to show students that chemical reactions occur as a normal part of their everyday lives.
• Collaborate with the home economics teacher to enhance the students understanding of the chemistry involved in cooking and using appropriate substitutions.
• Develop a forensic scenario to complement this activity.

Sample Data

Answers to Questions

1. Based on your observations and the data recorded in the Data Table, what is the composition of your unknown? Hint: The unknown powder may be any combination of the four powders. Why do you believe this?

   Compare student’s answer with unknown key.

2. In what practical situations would the identity of a powder need to be determined?

   Student’s answers will vary, but may include poisonings, crime scenes, drug identification, etc. Accept all reasonable answers.

3. List other methods one might use to differentiate these or other similar-looking powders.

   Student’s answers will vary, but may include microscopic investigations, color, texture, particle size, odor, etc. Accept all reasonable answers.

Introduction

Be a forensic scientist and identify an unknown powder that is commonly found in the kitchen using some very basic chemical and physical tests.

Concepts

• Chemical reactions
• Solubility
• Melting point
• Indicators

Background

It is critical in many real-life situations to have a test to determine the identity of a substance. All of the white powders included in this kit are items that are commonly found in the kitchen. Three powders are identified using common household liquids and heat is used to determine the identity of the fourth powder. From forensic science to medical emergencies, simple and straightforward determination of sample identities are the first steps in carrying out successful problem solving.

The powders include powdered salt, powdered sugar, corn starch, and baking soda. Powdered salt is sodium chloride or table salt crystals that have been ground into a powder. It is also commonly referred to as popcorn salt. Powdered sugar is used in candy making and baking and is also referred to as confectioner’s sugar. Corn starch is used to thicken sauces when cooking. Baking soda, also called sodium bicarbonate, is used as a cleaner and to make baked goods rise.

Each of the four identity tests is able to distinguish one of the white powders from the other three. Three of the tests use the different properties of water, vinegar, and iodine solution to make the distinction. Of course, water is the most common item found in any kitchen. Just turn on the faucet and it comes pouring into the sink. Water is used in this activity to determine the rate of solubility of four common powders. Vinegar is an acidic solution used in cooking and as a condiment. In this activity, because it reacts readily with a base, it is used to indicate if a powder is basic. Iodine is commonly found, although not in the kitchen, in the medicine cabinet as an antiseptic. Tincture of iodine is applied to cuts and scrapes to kill germs and iodine is used in this activity to indicate the presence of starch. The fourth test uses the low melting point of one of the powders to differentiate it from the others.

Experiment Overview

The purpose of this activity is to develop a procedure to identify four food-grade white powders using common household liquids and heat. After procedures are developed, an unknown will be analyzed to determine which of the four powders are present.

Materials

Safety Precautions

Avoid coming in contact with the iodine starch indicator. It will stain skin and clothing. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

1. Obtain approximately 2 g of each of the four powders (sugar, salt, corn starch and baking soda) in a weighing dish.
2. Using a marker, label each quadrant of the Petri dish with the name of one of the four powders (sugar, salt, corn starch and baking soda). Labels should be written on the bottom-side of the dish.
3. Using a marker, label each pipet with the name of one of the three liquids (vinegar, water and iodine starch indicator).
4. Using a spatula, place approximately 0.5 g of each powder in the appropriate quadrant.
5. Using a pipet, place eight to ten drops (about 0.5 mL) of vinegar on each powder and observe.
6. Record the results in the data table.
7. Wash and dry the Petri dish according to the instructor’s direction.
8. Using a spatula, place approximately 0.5 g of each power in the appropriate quadrant.
9. Using a pipet, place eight to ten drops (about 0.5 mL) of iodine starch indicator on each powder and observe.
10. Record the results in the data table.
11. Wash and dry the Petri dish according to the instructor’s direction.
12. Using a spatula, place approximately 0.5 g of each power in the appropriate quadrant.
13. Using a pipet, place eight to ten drops (about 0.5 mL) of water on each powder and observe.
14. Record the results in the data table.
15. Obtain a watch glass and, using a spatula, place approximately 0.5 g of each powder in four separate piles.
16. Heat the watch glass on a hot plate on a medium-high setting for about two minutes and observe.
17. Record the results in the data table.
18. Remove the watch glass from the hot plate using beaker tongs, place it on a ceramic fiber square, and allow it to cool.
19. Obtain 2 g of an unknown powder from your instructor. Record the unknown’s number in the data table.
20. Wash and dry the Petri dish according to the instructor’s direction.
21. Label three sections with the name of each of the three liquids (vinegar, iodine and water).
22. Using a spatula, place approximately 0.5 g of the powder in the center of each section of the Petri dish.
23. Using the dedicated pipet for each liquid, place eight to ten drops (about 0.5 mL) of each liquid on the powder in the corresponding section of the Petri dish and observe.
24. Record the results in the data table.
25. Obtain a watch glass and, using a spatula, place approximately 0.5 g of the powder in a pile in the center of the watch glass.
26. Heat the watch glass on a hot plate on a medium-high setting for about one minute and observe.
27. Remove the watch glass from the hot plate using beaker tongs, place it on a ceramic fiber square, and allow it to cool.
28. Record the results in the data table.
29. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

13034_Student1.pdf