Chemical and Physical Property Performance Test

Description: Students will test physical and chemical properties of four known substances to help them identify an unknown mixture.

Materials: Student worksheet, 4 substances (flour, salt, baking soda, and sugar) alcohol burner or other heat source, wire stand, 4 test tubes, test tube rack, aluminum foil (10 cm X 10 cm), dilute (.1 M) HCl acid, water, hand lens, goggles, spoon,

Time required: 40-60 minutes

Student background needed: Students should be familiar with the definition of chemical and physical change. They should have had laboratory safety instruction and be aware of where emergency equipment is stored.

Notes to teacher.

The four recommended substances will all react or behave differently in at least one way from the others. Mixing sugar and baking soda (equal amounts) will create the “unknown”. The “unknown” will melt when heated, like sugar, and fizz in acid, like baking soda.

Safety note: Caution students to only heat a small amount of each substance. Sugar and flour both burn well and will make a large, smelly cloud of smoke and flame if large (more than ½ a teaspoon) quantities are used. Using a hot plate will reduce the chance of flame but requires a lot of hot plates.

Procedures

  1. Hand out student worksheet and explain procedures and where materials will be found to students.
  2. Allow students time to complete lab.
  3. Summarize class results and ask students to make conclusions.

Sample Scoring Guide.

  1. Data recorded…………………………………………………………10 pts
  2. Unknown correctly identified………………………………………….5 pts
  3. Student is on task and cleans up properly ………………………...…...5 pts
  4. Questions correctly answered…………………………………….…...10 pts

Answers to questions:

  1. Physical properties tested are: observations under hand lens, dissolving in water
  2. Chemical properties tested are: reaction to heat, reaction to acid
  3. Salt and sugar are white, crystalline, dissolve in water, do not react in acid(except to dissolve in the water)
  4. Salt and sugar react differently to heat and taste different.
  5. The unknown should be baking soda and sugar.
  6. The unknown melts with heat like sugar and fizzes in acid like baking soda.
  7. Yes. Salt looks like sugar, dissolves like sugar, heats like baking soda. It could “hide” behind these two substances in the mixture.

Student Data Sheet

Name______

Period______

Title: Observing Substances

Purpose: In this lab activity you will test chemical and physical properties of 4 known substances and use the information collected to identify a mixture containing at least two of them.

Materials: flour, salt, baking soda, and sugar, unknown, alcohol burner or other heat source, wire stand, 5 test tubes, test tube rack, 5 pieces of aluminum foil (10 cm X 10 cm), dilute HCl acid, water, hand lens, goggles, spoon,

Procedures:

  1. Tear a sheet of paper into 5 pieces and write the name of one of the substances on each. Place a teaspoon of the substance on the correct papers.
  2. Observe each substance with the hand lens and record your observations in the data table.
  3. Fill the 5 test tubes one-half full of water. Add a pinch of one substance to a tube. Gently shake the tube and record what happens to the substance. Repeat for each substance.
  4. Empty the test tubes and add a pinch of one sample to a tube. Add a few drops of hydrochloric acid. Record what happens. Repeat for each tube.
  5. Make a four sided “box” out of your aluminum foil. Place a small amount of a substance in it. Place on wire stand then ask your teacher to light the burner. Put the wire stand over the burner and watch the reaction of the substance to heat. Record your data. Repeat with each substance.

Data:

Substance

/ Observations with hand lens / Reaction to water / Reaction to acid / Reaction to heat
Flour
Sugar
Baking Soda
Salt
Unknown

Analysis:

1. Which procedures tested for physical properties?

  1. Which procedures tested for chemical properties?
  1. Describe two ways salt and sugar are alike:
  1. What are two ways salt and sugar are different?
  1. What is the “unknown”?
  1. What evidence supports your answer to #5?

7. Could salt be in the unknown? Why or why not?

Conclusions:

Was your unknown correctly identified? Why or why not? What could you have done better in this lab?