Pre-AP Chemistry
Instructor: Mr. Malasky
Laboratory: Physical and Chemical Changes
Background
Matter has properties that help us identify and describe it. Properties can be considered physical or chemical. Physical properties include things like: color, odor, density, hardness, solubility, shape, and melting point. They are considered physical because they can be detected without changing the composition of the material. In a physical change, no new substance has formed, but the appearance likely has changed. Chemical properties are determined by a reaction of a substance with another substance. A new substance with new properties is formed during the chemical reaction. Evidence that a chemical change occurred can come from: a temperature change, release of a gas, change in color, production of or change in odor, formation of a precipitate, and identifying a new substance with new chemical properties.
A few changes may be difficult to know at first if they are physical or chemical. The basic test is to ask: what is being altered? If atoms of a substance have been rearranged and changed, it is a chemical change. If not, it is a physical change. This lab will allow you to look at changes and classify them as physical or chemical, based on the observations you make.
Materials burner test tubes w/rack food coloring (aq) acetic acid (aq) stirring rod
100 ml beaker
30 ml beaker barium nitrate (aq) copper samples (s) watch glass scoopula sulfur (s) cupric sulfate (aq) sodium sulfate (aq) ice cube sodium bicarb (s) iron (s)
S/Fe tube mixture mossy zinc (s) conc nitric acid (aq) tongs magnet sugar
Al dish
Methods - complete each of the individual tasks, recording results and conclusions by reaction number.
1. Obtain a square of copper. Hold the copper square on the sides using tongs. Place it in the inner cone
of a nonluminous burner flame for a couple of minutes. Remove, cool, and observe. Discard in trash.
2. Add 4 drops of food coloring to a 100 ml beaker that has 80 ml of tap water. Observe. Stir. Observe.
Rinse beaker at sink.
3. Measure approximately 5 ml of barium nitrate and 5 ml of sodium sulfate into separate test tubes.
Combine the contents into one tube. Observe. Rinse tubes at sink.
4. Place a scoopula of sodium bicarbonate into a test tube. Measure approximately 5 ml of acetic acid
in a separate test tube. Pour the acetic acid into the sodium bicarbonate test tube. Observe. Rinse
tubes at sink.
5. Obtain an ice cube and place on a watch glass. Observe initially and observe again in several
minutes. Discard any remains in sink.
6. Obtain 5 ml of cupric sulfate solution and add to a test tube. Add a few pieces of mossy zinc. Allow
five minutes for the reaction to occur. Observe. Discard any liquid in the sink and solid in the trash.
7. Observe the solid sulfur and iron samples provided. Obtain a tube containing a S/Fe mixture. Move
a magnet around the bottom and sides of the tube and observe. Return the tube to same location.
8. Place a scoopla of sugar in an aluminum dish. Flip the burner flame (no cone, Al melts at 660 o
C) to
heat the sugar for about a minute. Observe. Allow to cool, and then discard in trash.
9. UNDER THE FUME HOOD, take a small copper sample and place it in a 30 ml beaker. Add
about 10 ml of nitric acid (conc). Allow the change to take place. When complete, add water from
the wash bottle until a change is evident. Note changes. Rinse beaker once the reaction is over.
Questions
1. Provide an example of how metal could be physically changed.
2. What class of matter is the initial copper sample in steps 1 and 9?
3. What is a precipitate?
4. What are the common names for the two substances used in method #4?
5. Why was method #9 done under the fume hood?