Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Determine the number of unknown liquids that will be used during this laboratory activity.
2. The unknown liquids may be any combination of the four liquids included in the kit. The following is one suggestion for the combination and numbering of unknowns:
   {12761_Preparation_Table_1}
3. To prepare any of the unknowns, combine equal amounts of each liquid in a test tube and mix. Keep in mind that each group will need approximately 9 mL of each unknown assigned.
4. Label the test tube with the number of the unknown liquid and place in a test tube rack.
5. Cut the brown paper into thirty 4" x 4" squares, enough for each group to have two.

Safety Precautions

The iodine starch indicator solution may be irritating to skin and eyes. The acetone is slightly toxic and flammable. Avoid open flames or anything hot. 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. Acetone may be disposed of according to Flinn Suggested Disposal Method #18a. Hydrogen peroxide may be disposed of according to Flinn Suggested Disposal Method #22a. Vinegar may be disposed of according to Flinn Suggested Disposal Method #26b and baking soda may be disposed of according to Flinn Suggested Disposal Method #26a. Waste solutions from this activity may be disposed of according to Flinn Suggested Disposal Method #26b.

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.
• Purchase the store-labeled counterparts of each kit item 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 once they are brought into the science laboratory. Students should not eat or taste any of these items to determine their identity.
• Allow the paper to dry in the hood to speed up evaporation.
• It may be necessary to swirl the test tube when using iodine to detect hydrogen peroxide to make the bubbles more visible.
• For best results, use fresh hydrogen peroxide. The concentration of hydrogen peroxide will slowly decrease over time due to decomposition. As the concentration of hydrogen peroxide decreases, the time for bubbles to form when using iodine to detect hydrogen peroxide increases.

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 other common household functions using these chemicals.

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 liquid? What evidence supports this conclusion? Hint: The unknown liquid may be any combination of the four liquids.

   Compare students’ answer with unknown key.

2. In what practical situations would the identity of an unknown liquid need to be determined?

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

3. List other ways one might differentiate these or other similar-looking liquids.

   Students’ answers will vary, but may include odor, reactivity, conductivity, flammability, etc. Accept all reasonable answers.

Introduction

Become a forensic scientist! Using some basic chemical and physical properties, identify four liquids commonly found in the kitchen and use the results to determine the identity of an unknown liquid.

Concepts

• Chemical reactions
• Analytical/forensic chemistry
• Indicators
• Miscibility

Background

It is important in many real-life situations to have a test to determine the identity of a substance, from forensic tests that determine the identity of a poison to environmental tests that determine pollutants and their sources. In this kit, liquids that are commonly found in the kitchen or around the home, hydrogen peroxide, vinegar, oil and acetone will be tested. Hydrogen peroxide, because it is a powerful oxidizer, is used as a disinfectant. Vinegar is an acidic solution used in cooking and as a condiment. Oil is used in many applications including keeping food from sticking to nonfood surfaces. Acetone may be used as a solvent to remove fingernail polish.

The indicators used to identify the liquids are baking soda, brown paper, plastic, and iodine solution. These are chemicals found in many homes. Baking soda, also called sodium bicarbonate, is used as a cleaner and to make baked goods rise. In this activity, because it reacts readily with an acid, it is used to indicate which liquid is acidic. Iodine solution is commonly found in the medicine cabinet as an antiseptic. The alcohol solution, or tincture, of iodine is applied to cuts and scrapes to kill germs. Only hydrogen peroxide, an oxidizer, will react with the iodine solution to produce bubbling. Acetone is used as a solvent. Because acetone is a polar substance, it will dissolve polar plastics. Dripping acetone on a polar plastic will cause the plastic to become clouded as it is dissolved. The brown paper can be found as paper grocery or lunch bags. Oil will create a permanent translucent spot on the paper, while the other liquids create spots that will disappear upon drying. Oil is also immiscible, meaning it will not mix with the other substances in this kit.

Experiment Overview

The purpose of this activity is to identify four common, clear liquids using items commonly found in the kitchen. A known standard will be given for comparison and matched against the test results of an unknown.

Materials

Safety Precautions

Avoid skin contact with the iodine starch indicator. It will stain skin and clothing and is irritating to skin and eyes. Hydrogen peroxide is a skin and eye irritant; avoid all tissue contact. Acetone is flammable and toxic by ingestion or inhalation. Do not smell this material. Avoid working near open flames or anything hot. 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 four test tubes and a test tube rack.
2. Using a wax pencil or marker, label each of the four test tubes and four pipets with the name of one of the liquids (vinegar, hydrogen peroxide, oil and acetone). Label the other pipet as “unknown.”
3. Obtain a square of brown paper.
4. Using a wax pencil or marker, divide the paper into quadrants and label each section with the name of one of the four liquids (vinegar, hydrogen peroxide, oil and acetone).
5. Using the appropriate pipet, place 4 drops of each liquid on its labeled spot on the paper.
6. Allow the paper to dry (approximately 30 minutes) and observe.
7. Record your observations in the data table.
8. Weigh out approximately 2 g of baking soda. Use a spatula to place equal amounts in each of the four test tubes.
9. Using the appropriate pipet, place approximately 2 mL (40 drops) of each of the four liquids into the appropriate test tube and observe.
10. Record your observations in the data table.
11. Wash and dry the test tubes according to the instructor's directions.
12. Using the appropriate pipet, place approximately 2 mL (40 drops) of each of the four liquids into the appropriate test tube.
13. Place eight to ten drops of iodine starch indicator into each liquid using a pipet.
14. Observe the liquid for approximately five minutes for the formation of bubbles.
15. Record your observations in the data table.
16. Wash and dry the test tubes according to the instructor’s directions.
17. Obtain two plastic slides from the instructor.
18. Using a wax pencil or marker, divide each plastic slide in half and label each section with the name of one of the liquids (vinegar, hydrogen peroxide, oil and acetone).
19. Using the appropriate pipet, place 4 drops of each liquid on the appropriate spot on the slide and observe.
20. Record your observations in the data table.
21. Obtain a test tube of unknown liquid from your instructor.
22. Record the number of the unknown liquid in the data table.
23. Record the initial observations of the liquid in the data table.
24. If there is more than one layer of liquid, perform each of the following tests with each layer.
25. Obtain a square of brown paper.
26. Using the pipet labeled “unknown,” place 4 drops of the liquid on the paper.
27. Allow the paper to dry (approximately 30 minutes) and observe.
28. Record the results in the data table.
29. Weigh out approximately 0.5 g of baking soda and, using a spatula, place it in a test tube.
30. Using the pipet labeled “unknown,” place approximately 2 mL (40 drops) of the unknown liquid into the test tube and observe.
31. Record your observations in the data table.
32. Wash and dry the test tube according to the instructor’s directions.
33. Using the pipet labeled “unknown,” place approximately 2 mL (40 drops) of the liquid into a test tube.
34. Place eight to ten drops of iodine starch indicator into the liquid using a pipet.
35. Observe the liquid for approximately five minutes for the formation of bubbles.
36. Record your observations in the data table.
37. Wash and dry the test tube according to the instructor’s directions.
38. Obtain one plastic slide from the instructor.
39. Using the pipet labeled “unknown,” place 4 drops of the liquid on the plastic slide and observe.
40. Record the results in the data table.
41. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

12761_Student1.pdf