PHYSICAL AND CHEMICAL CHANGE
Lab #2
Purpose:
To investigate the criteria used to distinguish between physical and chemical changes in matter.
Materials: see lab handout
Safety: see handout
Hypothesis: The differences between physical and chemical changes can be determined by macroscopic observations.
Procedure:
Day one: (Part A)
1. Step one:
a. Label a separate, small piece of paper for each of the seven substances to be examined.
b. Place the magnesium on the paper labeled, “magnesium”.
c. Using a scoop, transfer a pea-sized sample of the other substances to their correctly labeled papers.
d. The seven substances are: Magnesium (Mg), Sulfur (S), iron filings (Fe), sodium hydrogen carbonate (NaHCO3), sodium chloride (NaCl), table sugar (C12H22O11), sand (SiO2).
2. Step two: Examine each substance with a magnifying glass and record your observations in Data Table 1.
3. Step three: Test the effect of a magnet on each substance by passing the magnet under the piece of paper.
4. Step four: In separate small test tubes, test the solubility of each substance by mixing a small amount of each sample with 3mL of distilled water. “Flick” each test tube to mix the contents.
5. Step 5: Return the strip of magnesium ribbon in the test tube to its paper. Follow instructions for disposal of other materials.
6. (Part B step 6)
a. Mix the iron filings and sulfur on a clean piece of paper.
b. Examine with a magnifying glass and test the effect of a magnet by passing the magnet under the paper.
c. Record observations in Data Table 2. Give this mix to your teacher at the end of the period.
Data Table Day One
Sulfur, S
Iron filings, Fe
Sodium hydrogen carbonate, NaHCO3
Sodium Chloride, NaCl
Sucrose, C12H22O11
Sand, SiO2
Magnesium, Mg
System / Observations
Fe and S mixture
-tested with a magnet
Day two: (Part B)
7. Step seven:
a. Mix the sodium chloride and sand on a clean piece of paper.
b. Examine with a magnifying glass and test with a magnet.
c. Record observations in Data Table 2.
8. Step eight:
a. Transfer the salt and sand mix to a clean 100mL beaker.
b. Add 30mL of tap water and stir.
c. Record observations in Data Table 2.
d. Filter the mixture and record observations.
e. Pour 10mL of the liquid (filtrate) into an evaporating dish and heat gently until the water has completely evaporated.
f. Examine the residue in the dish and the residue on the filter paper.
g. Record observations.
9. Step nine:
a. WARNING: USE THE BLUE GLASS TO LOOK AT THE BURNING MAGNESIUM.
b. Position a watch glass near the Bunsen burner.
c. Using crucible-tongs, grasp one end of the Mg strip and hold it in the flame until ignition.
d. Hold the burning strip above the watch glass to catch the ashes. DO NOT LET THE BURNING MG LAND ON THE GLASS.
e. Record observations.
10. Step ten:
a. Place the unburned Mg into a test tube.
b. Place the ashes (combustion product) into another test tube.
c. Add 10 drops of 6M HCl to each tube.
d. Feel the bottom of each tube.
e. Record observations.
Day Two Data Table
System / ObservationsNaCl and sand mixture
-mixed with water
-filtered
-filtrate and heat
Mg
-burned in air
Mg
-reacted with 6M HCl
Mg ashes
-reacted with 6M HCl
Day three: (Part B cont.)
11. Step eleven:
a. Put a small scoop of the sucrose into a test tube.
b. Heat gently and observe changes.
c. Check for odors.
12. Step twelve:
a. Transfer the NaHCO3 to a test tube.
b. Carefully add 15 drops of 6M HCl.
c. Touch the bottom of the tube.
d. Record observations.
13. Step thirteen:
a. Dispose of all compounds as per instructions.
Day Three Data Table
System / ObservationsSucrose, C12H22O11
-heated
NaHCO3
-reacted with 6M HCl
Fe and S mixture
-heated
-initial mass
-final mass
ANALYSIS AND CONCLUSIONS:
1. The following is a list of changes you observed in Parts B and C. Indicate whether each change was a physical change or a chemical change and give evidence for your answer.
a. Mixing iron and sulfur (Part B, Step 6)
b. Mixing salt, sand, and water (part B, Step 8)
c. Burning Mg (Part B, Step 9)
d. Mixing Mg and the ashes with HCL (Part B, Step 10)
e. Heating sucrose (Part B, Step 11)
f. Mixing NaHCO3 and HCl (Part B, Step 12)
g. Heating iron and sulfur. (Part C, Step 14)
2. Was mass conserved in the reaction of iron and sulfur? Explain.
3. Except for the reaction between iron and sulfur, none of the reactions in the experiment can be used to demonstrate the law of conservation of mass. Why?
4. How do you decide whether what you observe is a physical or chemical property?
5. What is the difference between a physical and a chemical change?
6. State in your own words the law of conservation of mass.