UCLA, GK-12 Science and Engineering of the Environment of Los Angeles

Physical and Chemical Changes Lab

Pre-Lab Discussion:

Chemistry is the study of matter and the changes it undergoes. These changes can be broken down into two classes – physical changes and chemical changes. In a physical change, one or more physical properties of a substance are altered. Examples of such physical properties include size, shape, color and physical phase. Grinding, melting, dissolving, and evaporating are all physical changes. No new substances are formed as a result of a physical change.

A chemical change results in the formation of one or more “new” substances. These new substances differ in chemical properties and composition from the original substance. The rusting of iron and the burning of paper are two examples of chemical change.

This experiment will help you to understand the difference between physical and chemical change and to recognize each type of change when it occurs.

Purpose: Recognize and distinguish between chemical and physical changes.

Equipment:

Lab balance / Test tube rack / Mortar and pestle
Lab burner / Test tube holder / Magnet
4 test tubes / Watch glass / Safety goggles
Lab apron

Materials:

Copper sulfate pentahydrate - (CuSO4· 5H20) / Silver nitrate (0.1M AgNO3)
Sulfur (S), powdered / Magnesium Ribbon (Mg)
Paper (5cm x 10cm)
Sodium chloride (NaCl) / Iron fillings (Fe) / 250mL beaker
Hydrochloric acid (6M HCl) / Wood splint / Weighing paper

Safety:

When heating a substance in a test tube, be sure that it is pointed away from others. Handle acids with extra caution. Wear goggles at all times and report any spills to your teacher. Be sure to give glass enough time to cool before you touch it since glass retains heat.

Lighting the Bunsen Burner:

1. Make sure the air vent near the bottom of the Bunsen burner barrel is closed.

2. Position the flint striker directly over the top of the Bunsen burner barrel.

3. Turn on the gas.

4. Light the burner using the flint striker (hold striker in non-dominant hand while pushing down with the thumb of your dominant hand against the flint, scraping hard enough to generate a spark).

5. Once burner is lit, open the air vent.

Procedure:

Note and record all observations in your data table. (Be sure to record observations, before, during and immediately after each step in the procedure.)

  1. Tear a piece of paper (about 5cm x 5cm) into small pieces. Set a watch glass on the lab table and place the pieces of paper on the glass. Light the wood splint with the lab burner and use it to ignite the paper.
  2. Using a wood splint, add a small amount of NaCl (sodium chloride) to a test tube. Add about 1 inch of water to the NaCl and shake the contents of the test tube.
  3. Next, add 3 drops of 0.1M AgNO3 (silver nitrate) to the NaCl-water mixture.

**Pour the contents of the test tube into a designated waste beaker. Do not rinse it down the sink!

  1. Obtain one piece of cut magnesium ribbon. Fold the piece of Mg and place it into a test tube and add 4 to 5 drops of 6M HCl (hydrochloric acid).

CAUTION: Use extreme care when handling this acid. It will cause severe burns if allowed to come in contact with the skin.

Touch the bottom of the test tube with your fingertip. Rinse contents of test tube in the sink.

  1. Use a mortar and pestle to grind 1 or 2 crystals of CuSO4·5H2O into a uniform powder. Place the powder into a test tube. Heat gently over a burner flame for 2 minutes. Set the test tube aside to cool. Once the test tube is cool to the touch, add 1 to 2 drops of water to the test tube.

** Pour the contents of the test tube into a designated waste beaker. Do not rinse it down the sink!

  1. Using the lab balance and a piece of weighing paper for each sample, measure out 0.5g of iron filings and 0.3g of sulfur. Test each sample with a magnet by running the magnet under the weighing paper. **Do not put the magnet directly onto the substances! Mix the two samples thoroughly in a test tube. Run the magnet along the bottom and sides of the test tube.

Fill the 250mL beaker with water. Heat the iron-sulfur mixture in a burner flame for several minutes until the mixture is “glowing” (red) hot. Immediately put the hot test tube into the water in the beaker. (The test tube should crack.) Carefully remove the substance from the test tube onto a paper towel using a wood splint. Probe the substance with the wood splint and test it with the magnet.

**Dispose of the broken test tube, glass, and final product into the trash can.

CLEAN UP PROCEDURES:

·  Rinse and dry all glassware.

·  Throw out any used paper or wooden splints

·  Clean and dry lab tables.

·  Place all materials neatly in lab bins and return to cart.


Name______

Period______Date______

Data Table:

Step / Reaction / What physical changes do you observe? How do you know it is a physical change? Give evidence. / What chemical changes do you observe? How do you know it is a chemical change? Give evidence.
1. / Paper / Change:
Evidence: / Change:
Evidence:
2. / NaCl and H2O / Change:
Evidence: / Change:
Evidence:
3. / NaCl and AgNO3 / Change:
Evidence: / Change:
Evidence:
4. / Mg ribbon / Change:
Evidence: / Change:
Evidence:
5. / CuSO4·5H2O / Change:
Evidence: / Change:
Evidence:
6. / Fe and S / Change:
Evidence: / Change:
Evidence:


Pre-lab Questions:

1.  What is a physical change?

2.  What is a chemical change?

3.  Determine which of the following characteristics are physical or chemical changes:

a.  Heat released after mixing two chemicals f. Precipitate formed

b.  Object broken into small bits g. Liquid boiled into gas

c.  Light emitted after a reaction h. Solid melting into a liquid

d.  Gas condensed into a liquid

e.  Gas bubbles formed after mixing two chemicals together

4.  Determine whether the following are physical or chemical changes:

a.  Breaking an egg shell f. Melting a glass

b.  Frying an egg g. Cutting grass

c.  Grass fire h. Breaking a glass

d.  Blowing bubbles into chocolate milk i. Soda can explodes in freezer

e.  Mixing vinegar and baking soda

5.  Provide 3 examples of physical changes not listed above and indicate why (provide evidence).

6.  Provide 3 examples of chemical changes not listed above and indicate why (provide evidence).

Post-Lab Questions: (Answer in complete sentences)

1.  Name two possible things you might see that would give you an indication that a chemical change has taken place. Use examples from THIS lab.

2.  The following changes do not always indicate chemical change. Give examples of an instance from THIS lab where these changes might be the result of a physical change.

a.  Change of color

b.  Apparent loss of mass

c.  Apparent disappearance of a substance

3.  How can substances in a mixture be separated? How can substances in a compound be separated? Use examples from this experiment in your explanations.

Conclusion:

What did you learn about physical and chemical changes and telling the difference between the two? What did you like/dislike about the lab? What were possible sources of error? What would you do differently to improve the lab?