Physical and Chemical Changes LabName ______

25 PointsPeriod ______Date ______

Introduction: As you read this it is probably fall. Summer flowers are fading and dying. Leaves are changing from green to red, yellow and orange. All these changes involve chemistry.

As you have learned, chemistry is the study of matter and the changes that it undergoes. These changes can be classified as physical, chemical, or nuclear. This lab will focus on physical and chemical changes. When a physical change occurs, the physical properties of a substance – such as its size, shape, state, or density – are altered, but its chemical composition remains the same. Examples of physical changes include melting ice, crushing gravel, tearing paper, grinding pepper, and boiling water. No new substances are formed as a result of these changes.

Chemical changes, also known as chemical reactions, result in the formation of one or more new substances with different chemical properties and compositions from the original material. Examples of chemical changes include plants dying, leaves changing color, paper burning, bananas ripening, bread baking, or iron rusting. Some signs of chemical changes include a change in color, the formation of a precipitate (a new solid substance that settles out of solution), the production and release of a gas, or a change in temperature.

In this investigation, you will conduct tests on several substances and then use your data to determine whether the resulting changes were chemical or physical. As you observe each change, remember to ask yourself, “Has the change altered the identity of the substance?”

Pre-Lab Questions:

1. What are the 4 observable signs that indicate a chemical change is taking place?

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2. Define precipitate as it relates to this lab. ______

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3. Identify the following as either a chemical (C) or physical (P) change:

a. burning wood______

b. dry ice changing to a gas______

c. freezing water______

d. ripening fruit ______

e. dissolving sugar in water______

4. Why are you instructed to feel outside the test tube after two chemicals are mixed, as in Steps 5 and 6

of this investigation? ______

5. What are the safety cautions you need to observe during this investigation? ______

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Problem: How can you recognize and differentiate between physical and chemical changes in matter?

Procedure:

  1. Put on your apron and goggles. Break off a small piece of wax from the bottom of a birthday candle and place it in a DISPOSABLE test tube. Holding the test tube with tongs, heat it gently over the burner until the wax completely melts. Place the test tube in a beaker until it cools and then throw test tube in trash. Record results in Data Table.
  1. With matches, light larger candle. Secure candle to the glass square by dripping wax onto the square and then holding the base of the candle in to the molten wax until the wax hardens. Allow the candle to burn for two minutes and blow out. Record results in Data Table.
  1. Break off a small piece of paper and place it in a watch glass. Place watch glass on insulating pad and ignite paper with matches. Record results in Data Table.
  1. Measure 5mL of water in a graduated cylinder. Pour water into a test tube a add a small amount of sodium chloride. Stir the contents to mix. Using eye dropper, add 10 drops of silver nitrate (0.1 M AgNO3) to the NaCl-water mixture. Record results in Data Table. NOTE: SILVER NITRATE IS TOXIC AND CAN STAIN YOUR SKIN. WASH ANY SILVER NITRATE OFF YOUR SKIN IMMEDIATELY.
  1. Obtain a small piece of Magnesium ribbon and place it in a test tube. Add a few drops of hydrochloric acid to the test tube. Record results in Data Table.. NOTE: HYDROCHLORIC ACID IS HIGHLY CORROSIVE AND CAUSES BURNS. WASH ANY HYDROCHLORIC ACID OFF YOUR SKIN IMMEDIATELY.
  1. Grind several crystals of copper sulfate pentahydrate (CuSO4 5H2O) with the mortar and pestle. Place a microspatula (small amount) of the powder into a test tube. Heat gently over a bunsen burner for 2 minutes. Allow to cool for 5 minutes; then add a few drops of water. Touch the bottom of your test tube with your fingertip. Record your observations in the Data Table.
  1. Using two pieces of weighing paper, place a SMALL amount of sulfur in one holder and a SMALL amount of iron filings in the other holder. Run the magnet along the side of the holders. Then, mix the two substances into one of the holders and run the magnet along the side of the holder. Record results in Data Table.
  1. Heat the iron-sulfur sample under the fume hood for several minutes until the mixture glows. CAUTION: Do not carry out this step unless a working hood is available. Noxious fumes are produced that must be evacuated by a fume hood. All the sample to cool for 10 minutes. Notice its appearance. Test with a magnet. Record results in Data Table.
  1. Clean up your work area and wash your hands before leaving the laboratory.

Observations: Data Table

STEP / Observations
BEFORE / DURING / AFTER
1
2
3
4
5
6
7
8

Critical Thinking: Analysis and Conclusions

  1. Indicate whether the following changes are physical or chemical. Explain your answer.

Change / Physical or
Chemical / Explanation
Melting candle wax
Burning candle wax
Tearing paper
Burning paper
Dissolving NaCl
Mixing NaCl and AgNO3
Adding HCl to Mg
Grinding CuSO4 · 5H2O
Heating CuSO4 · 5H2O
Mixing Fe and S
Heating Fe and S
  1. Name two possible indications that a chemical change has occurred, using examples from this investigation.

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  1. A change in color does not always indicate chemical change. Explain why it could be the result of a physical change. ______
  2. Answer the following questions using examples from this investigation to support your answers.
  1. How can substances in a mixture be separated? ______
  2. How can substances in a compound be separated? ______

Critical Thinking: Applications

1. Sodium chloride dissolves in water, leaving a clear homogenous mixture with no physical evidence of the crystals with which you started. Design an experiment that you could perform to separate the sodium chloride from the water.

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2. How could the experiment you designed in response to Question #1 differ if some sand was mixed in with the sodium chloride before it was added to water?

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