2-1 Discovery

Discovery 2-1 : Physical and Chemical Changes
Physical and chemical changes occur all around us everyday. It is useful to understand the
nature of these changes to help us understand the world we live in. We will be observing
several changes to determine the characteristics of a physical change and the characteristics of
a chemical change. Remember from Unit 1 that mixtures can be separated into substances by
a physical change and that compounds can be separated into elements by a chemical change.
A physical change does not alter the composition of a substance (Ex: tearing paper, crushing a
pill). In a chemical change (or chemical reaction), one or more substances change into new
substances (Ex: rotting food, burning gasoline).
Part A: What are some physical properties of substances?
1. Your teacher will assign one substance to your group. Obtain one spatula full of your
substance and place in a small beaker. In the table below, record the physical state at room
temperature (solid, liquid or gas) and color of your sample. Test the effect of a magnet by
running the magnet UNDER the beaker—Do NOT allow the magnet to touch the
substance in the beaker! Test the solubility by placing a pea-sized amount into a small
test tube and filling half-full with water. Cover the test tube with your thumb and invert
several times to mix. Wash your hands!!! Record your observations on your paper and on
the class data table.
Clean-up: Any substance that dissolved in water can be rinsed down the drain. Any
substance that did not dissolve can be disposed of in a paper towel in the trash can. Dry
and return the piece of magnesium and aluminum. To save materials, return unused
substances to their containers (we usually don’t do this).
Substance and
Effect of
in Water
aluminum, Al
sulfur, S
iron filings, Fe
salt, NaCl
sand, SiO2
magnesium, Mg
Part B: How can substances be changed?
Follow the instructions carefully and record your observations, determination of physical (P) or
chemical (C) change, and explanation of physical or chemical into the table on the back of this
page. Be sure to dispose of chemicals properly as indicated in the instructions.
1. Burning magnesium: Do not look directly at burning magnesium; look through film negative
or blue cobalt glass. Position a watch glass near the gas burner. Using tongs, grasp one end of
the strip of magnesium ribbon and hold it in the burner flame until the magnesium ignites.
Quickly position the burning magnesium so that the combustion product falls on the watch
glass. Compare the appearance of this product with that of the original magnesium. Record
your observations.
Clean-up: Throw the product in the trash can.
2. Iron-sulfur mixture
a. Mix a small scoop of iron filings and sulfur in a 100mL beaker. Examine the mixture and test
the effect of a magnet by passing the magnet UNDER the beaker—Do NOT allow the magnet
to touch the Fe or S in the beaker! Record your observations of color and magnetism.
Clean-up: Put the mixture in the beaker on the tray labeled “Fe-S mixture.”
b. Obtain a test tube that contains the Fe-S mixture that has been heated. Test the effect of the
magnet on this heated mixture. Record your observations of color and magnetism.
3. Salt-sand mixture
a. Mix a scoop of salt and sand in a 100mL beaker. Examine the mixture. Record your
b. Add approximately 25mL of water and stir. Record your observations.
c. Filter the mixture using filter paper and a funnel. What is left on the filter paper? Record
your observations. Continue to Part 3d as soon as you have some filtrate.
d. Heat about 3mL of the filtrate (liquid portion) in an evaporating dish on a hot plate. Heat it
gently on medium-high heat (Setting 7-8) until the filtrate has evaporated. Examine the dry
residue in the dish. What is it? Record your observations.
Clean-up: Remove the evaporating dish from the hot plate and place on a ceramic pad
or wire gauze to cool. Rinse all glassware with water and dry. Throw away the filter
4. Copper (II) chloride dihydrate and aluminum foil
a. Fill a 100mL beaker about one-fourth full of tap water. Add 2 spatulas of copper (II) chloride.
Use a stirring rod to stir the mixture until the crystals are completely dissolved. Use a digital
thermometer to measure the temperature of the solution. Record your observations and the
b. Place a loosely crumpled ball of aluminum foil in the solution. Stir the mixture for about 3-5
minutes. Measure the temperature. Record your observations and the temperature.
Clean-up: Pour the solution and solid in the “Copper Product” jar in the fume hood.
Rinse the beaker. Carefully rinse and dry the temperature probe.
1. Burning
2a. Iron/sulfur
2b. Heating
iron/sulfur mixture
3a. Salt/sand
3b. Salt/sand +
3c. Salt/sand/water
3d. Filtrate
4a. CuCl2 + water
4b. CuCl2 + Al
P or C
Explanation of Choice