Download Physical and Chemical Change

Physical and Chemical Change
Purpose: To investigate the criteria used to distinguish between physical and chemical changes
in matter.
Background: Have you ever thought of your eyes as powerful tools for studying chemistry?
Many of the properties of matter and the changes it undergoes can easily be determined
through careful observation. Physical properties include color, odor, density, solubility and the
state of matter. Chemical properties describe the changes that take place when new
substances are formed during a chemical reaction.
When matter undergoes a change, it is classified as either a physical change or chemical
change. During a physical change, only the size, temperature or physical state of the substance
changes. Melting, dissolving, grinding and evaporating are all physical changes. However,
chemical changes always result in the formation of one or more new substances. The rusting of
iron, during which the new substance iron (III) oxide forms from iron (Fe) and oxygen (O2), is an
example of a chemical change.
In this experiment you will observe a variety of materials and describe their physical properties.
You will then cause some of the substances to undergo changes. Based on your observations,
you will determine whether the changes are physical or chemical changes.
Materials:
 Safety goggles
 6 small test tubes
 1 test tube rack
 1 test tube holder
 2 100mL beakers
 1 funnel
 1 watch glass
 1 plastic wash
bottle
 1 glass stirring rod
 1 evaporating dish
 1 magnifying glass











1 crucible tongs
1 magnet
1 spatula
1 gas burner
1 ring stand
1 ring support
1 wire gauze
1 forceps
Coarse filter paper
9-10cm x 10cm
pieces of paper
Distilled water







Iron filings (Fe)
Sodium hydrogen
carbonate
(NaHCO3)
Sodium chloride
(NaCl)
Sucrose (C12H22O11)
Sand
Magnesium ribbon
(Mg)
6M hydrochloric
acid (HCl)
SAFETY FIRST!
 Wear safety goggles (All steps)
 Hydrochloric acid is very corrosive and can cause burns. (Steps 5, 6)
 Do not look directly at burning magnesium. View the magnesium reaction through exposed pieces of
film. Do not inhale the smoke that is produced when magnesium burns. (Step 4)
 Do not taste any of the substances or touch them with your hands.
 Hot glass looks just like cool glass. Once a test tube has been heated over an open flame, it may take
several minutes for it to cool. Be sure that test tubes are cool before handling them (Step 6)
 Magnesium is extremely flammable. Keep unused strips away from open flames (Step 4)
 Return or dispose of all materials according to the instructions of your teacher. (Step 8)
 When heating a test tube, never point the mouth of it at yourself or anyone else. (Step 6)
Procedure:
Record your observations in Data Table 1.
1. Mix the iron filings and sand on a clean piece of paper. Examine the mixture with a magnifying glass.
Test the effect of a magnet by passing the magnet under the paper. Separate the iron filings and
dispose of them in the trash can. Save the sand for step 2.
2. Mix the sodium chloride and sand on a clean piece of paper.
Transfer the salt-sand mixture to a clean 100mL beaker. Add
30mL of tap water and stir. Record your observations. Prepare a
filtration setup as shown. Filter the mixture and record your
observations. Pour 10mL of the filtrate into an evaporating dish.
Heat the dish gently until the filtrate has completely dissolved.
Examine both the dry residue and the wet residue on the filter
paper.
3. Position a watch glass near the gas burner. Using crucible tongs. Grasp one end of the 5cm strip of
magnesium ribbon and hold it in the burner flame until the
magnesium ignites. Quickly position the burning magnesium so that
the combustion products fall on the watch glass. Compare the
appearance of this product with that of the original magnesium
ribbon.
4. Place the unburned 1cm strip of magnesium and the combustion
product from the watch glass into separate test tubes. Add 10 drops
of 6M HCL to each tube. Feel the bottom of each test tube. Record
your observations.
5. Put half of your sucrose sample into a test tube. Heat the tube gently
in a burner flame and watch carefully for changes. Periodically
remove the tube from the flame and check for odors by wafting.
Now heat the residue in the test tube more vigorously for 1-2
minutes. After cooling the tube, use a spatula to scrape some of the
residue into a clean test tube. Examine the residue and test its
solubility in water.
6. Transfer sodium hydrogen carbonate sample into a test tube. Carefully add 5 drops of 6MHCl. Touch
the bottom of the test tube with your hand. Record your observations.
7. Follow your teacher’s instructions for proper disposal of materials.
Data Table 1: Observations of Physical and Chemical Changes
System
NaCl and Sand mixture
-mixed with water
Observation
-filtered
-filtrate allowed to evaporate
Mg
-burned
Mg
-reacted with 6M HCl
Mg Combustion product
-reacted with 6M HCl
C12H22O11
-heated
NaHCO3
-reacted with 6M HCl
Analyses and Conclusions:
1. The following is a list of changes you observed. Indicate whether each change was a physical or chemical change
and explain your answer.
a. Mixing salt, sand and water______________________________________________________________
_____________________________________________________________________________________
b. Burning magnesium____________________________________________________________________
_____________________________________________________________________________________
c. Mixing magnesium and the combustion product with HCl______________________________________
_____________________________________________________________________________________
d. Heating sucrose________________________________________________________________________
_____________________________________________________________________________________
e. Mixing sodium hydrogen carbonate and HCl. ________________________________________________
_____________________________________________________________________________________
2. How do you decide whether an observed property of matter is a physical or chemical property? _____________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
3. What criteria are used to distinguish between a chemical change and a physical change? ___________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
4. State in your own words the law of conservation of mass. ____________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________