5.42-1
SCIENCE EXPERIMENTS ON FILE™ Revised Edition
What Makes a Good Conductor?
Mary V. McCrary
Topic
Chemical bonding
Time
45 minutes
!
Safety
Adult supervision is required. Please click on the safety icon to view the safety
precautions.
Materials
conductivity apparatus (three pieces
of insulated copper wire, 6-V flashlight bulb, socket for bulb, 6-V DC
lantern battery)
graphite pencil “lead”
plastic ruler
small piece of rubber tubing
aluminum foil
small piece of stripped copper wire
mylar (from helium balloon)
1 tbs table salt
6–V DC battery
soapless steel wool
1 tbs baking soda
glass rod
1 tbs granulated sugar
wooden stick
1 L water
paper clip
small saucepan
charcoal stick
stove or hot plate
bulb
sample
© Facts On File, Inc.
SCIENCE EXPERIMENTS ON FILE™ Revised Edition
5.42-2
Procedure
PART A: SETUP
Set up the conductivity apparatus as shown in the figure.
PART B: METALLIC
AND
COVALENT BONDS
Elements classified as metals lose electrons easily. In fact, their electrons are free to
move among all the atoms in the substance. Atoms in a metallic element or in a
compound composed of different metals are held together by attractive forces between the nuclei and these freely moving electrons, and are good electrical conductors. These substances are said to have metallic bonds.
Elements classified as nonmetals and compounds composed of nonmetallic elements are held together by covalent bonds. Atoms in these substances share one or
more specific pairs of electrons. Their electrons are localized: They cannot move
freely throughout the substance, and thus these materials do not conduct electricity.
A few elements exhibit properties of both metals and nonmetals. They conduct
electricity in some forms and not in others. In their conductive form, they have metallic bonds; in their nonconductive forms, they are held together by covalent bonds.
1. Test the conductivity of the solid substances listed in data table 1. To do this,
touch both wires of your testing device to each sample. If the bulb lights up, the
sample is a conductor. Note the results by writing “yes” or “no” in the column
labeled “Conductivity.”
D ATA T A B L E 1
Substance
Conductivity
Bond type:
metallic or covalent
Exhibits properties
of metal or nonmetal
1. Glass rod (silicon, oxygen)
2. Aluminum foil
3. Steel wool (iron)
4. Mylar (a polyester: carbon,
oxygen, hydrogen)
5. Paper clip (nickel, iron)
6. Plastic ruler (polypropylene)
7. Rubber tubing (1,3 butadiene)
8. Copper wire
9. Charcoal stick (carbon)
10. Wooded stick (cellulose)
11. Graphite pencil “lead” (carbon)
2. After you have tested all the samples, go over your results and, in the appropriate column, write whether each substance exhibits properties of a metal or a
nonmetal. Note what bond type you think each has.
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5.42-3
SCIENCE EXPERIMENTS ON FILE™ Revised Edition
PART C: ELECTROLYTES
AND
NONELECTROLYTES
When a metallic and a nonmetallic element combine to form a compound, a different type of bonding takes place. This is called ionic bonding. In this type of bond,
atoms of the metal lose electrons, which are acquired by atoms of the nonmetal.
Thus, charged particles known as ions are formed. The metals that have lost electrons form positively charged ions, and the nonmetals that have gained electrons
form negatively charged ions. Although the compound is made up of charged particles, the numbers of negative and positive particles are always equal. Therefore, the
compound is electrically neutral. In its solid form, the substance’s charged particles
are not free to move around; therefore, as solids, compounds with ionic bonds do
not conduct electricity. However, when these compounds are melted or dissolved in
water, the charged particles (ions) are dissociated; that is, they are separated and
free to move about. In solution, these compounds are electrical conductors. Substances that conduct electricity in solution are called electrolytes; those that do not
are called nonelectrolytes.
1. For each of the substances listed in data table 2, test a solid sample for conductivity and note your results on the table.
D ATA T A B L E 2
Substance
Conductivity
as a solid
Conductivity
in solution
Bond type
Electrolyte or
nonelectrolyte
Sugar (dextrose: carbon,
hydrogen, oxygen)
Table salt (sodium chloride:
sodium and chlorine)
Baking soda (sodium
bicarbonate: carbon,
hydrogen, sodium, oxygen)
2. Put 1 tbs sugar into 250 mL water in a small saucepan, and bring the solution
to a boil, stirring to be sure it is dissolved. Test the boiling solution for conductivity, and note the results on the table.
3. Repeat step 2 for both the table salt and baking soda samples.
4. Based on your results, decide whether you think each of these compounds has
ionic or covalent bonds and whether each is an electrolyte or a nonelectrolyte.
Note your conclusions on the table.
5. Which of the solids in Part B were good conductors? Which were poor conductors? Which of the samples exhibited metallic properties?
6. The wires of your conductivity device are copper that is coated with rubber. Explain the role of each of these substances in your device.
7. Did any of the solid substances in Part C conduct electricity? Why or why not?
Did any of the solutions conduct electricity? Why do you think the solutions
were heated? Which substances are electrolytes?
© Facts On File, Inc.
SCIENCE EXPERIMENTS ON FILE™ Revised Edition
5.42-4
What’s Going On
The aluminum foil, steel wool, paper clip, copper wire, and pencil graphite all conduct electricity. The glass rod, mylar, plastic ruler, rubber tubing, charcoal stick, and
wooden stick do not conduct electricity. There are only four metals among the samples: aluminum, steel (iron), nickel, and copper. Although graphite conducts electricity, it is not considered a metal. It is a form of carbon, as is charcoal—which
does not conduct electricity.
Carbon is one of the few elements that, in different forms, exhibits both metallic
and nonmetallic properties. Electrons can move through copper but not through
rubber, so the copper wires are good electrical conductors and the rubber casing
serves as insulation. Both conductors and insulators are necessary for electrical current to be useful. If the rubber insulation around the conducting wire were replaced
by a conducting substance, current would not be directed through the wire but
would flow out uncontrollably in all directions. Air itself is a weak insulator, but
rubber is a stronger one and is commonly used in an electrical apparatus.
None of the solid substances conducts electricity for the reasons stated in Part C
of the procedure. The sugar has covalent bonds, and the salt and baking soda have
ionic bonds that do not conduct in solid form. The salt and baking soda solutions conduct electricity. They were heated to speed up the chemical reaction—dissociation—
that frees the charged particles and allows conductivity. If you test the saltwater when
it is cool, you will probably still observe conductivity, but it will be somewhat
weaker—the bulb will not glow as brightly. Salt and baking soda are electrolytes.
Connections
Because electrical current is the free movement of electrons, the way atoms combine in a substance, known as the substance’s bond type, determines its ability to
conduct electricity. In this project, you tested the conductivity of some solids and
solutions and related your results to the bond types of the samples tested.
© Facts On File, Inc.
Safety Precautions
READ AND COPY BEFORE STARTING ANY EXPERIMENT
Experimental science can be dangerous. Events can happen very quickly while you are performing
an experiment. Things can spill, break, even catch fire. Basic safety procedures help prevent serious
accidents. Be sure to follow additional safety precautions and adult supervision requirements for
each experiment. If you are working in a lab or in the field, do not work alone.
This book assumes that you will read the safety precautions that follow, as well as those at the start
of each experiment you perform, and that you will remember them. These precautions will not always
be repeated in the instructions for the procedures. It is up to you to use good judgment and pay attention when performing potentially dangerous procedures. Just because the book does not always
say “be careful with hot liquids” or “don’t cut yourself with the knife” does not mean that you should
be careless when simmering water or stripping an electrical wire. It does mean that when you see a
special note to be careful, it is extremely important that you pay attention to it. If you ever have a
question about whether a procedure or material is dangerous, stop to find out for sure that it is safe
before continuing the experiment. To avoid accidents, always pay close attention to your work, take
your time, and practice the general safety procedures listed below.
PREPARE
• Clear all surfaces before beginning work.
• Read through the whole experiment before you start.
• Identify hazardous procedures and anticipate dangers.
PROTECT YOURSELF
• Follow all directions step by step; do only one procedure at a time.
• Locate exits, fire blanket and extinguisher, master gas and electricity shut-offs, eyewash, and
first-aid kit.
• Make sure that there is adequate ventilation.
• Do not horseplay.
• Wear an apron and goggles.
• Do not wear contact lenses, open shoes, and loose clothing; do not wear your hair loose.
• Keep floor and work space neat, clean, and dry.
• Clean up spills immediately.
• Never eat, drink, or smoke in the laboratory or near the work space.
• Do not taste any substances tested unless expressly permitted to do so by a science teacher in
charge.
USE EQUIPMENT WITH CARE
• Set up apparatus far from the edge of the desk.
• Use knives and other sharp or pointed instruments with caution; always cut away from yourself
and others.
• Pull plugs, not cords, when inserting and removing electrical plugs.
• Don’t use your mouth to pipette; use a suction bulb.
• Clean glassware before and after use.
• Check glassware for scratches, cracks, and sharp edges.
• Clean up broken glassware immediately.
v
© Facts On File, Inc.
vi
Safety
SCIENCE EXPERIMENTS ON FILE™ REVISED EDITION
• Do not use reflected sunlight to illuminate your microscope.
• Do not touch metal conductors.
• Use only low-voltage and low-current materials.
• Be careful when using stepstools, chairs, and ladders.
USING CHEMICALS
• Never taste or inhale chemicals.
• Label all bottles and apparatus containing chemicals.
• Read all labels carefully.
• Avoid chemical contact with skin and eyes (wear goggles, apron, and gloves).
• Do not touch chemical solutions.
• Wash hands before and after using solutions.
• Wipe up spills thoroughly.
HEATING INSTRUCTIONS
• Use goggles, apron, and gloves when boiling liquids.
• Keep your face away from test tubes and beakers.
• Never leave heating apparatus unattended.
• Use safety tongs and heat-resistant mittens.
• Turn off hot plates, bunsen burners, and gas when you are done.
• Keep flammable substances away from heat.
• Have a fire extinguisher on hand.
WORKING WITH MICROORGANISMS
• Assume that all microorganisms are infectious; handle them with care.
• Sterilize all equipment being used to handle microorganisms.
GOING ON FIELD TRIPS
• Do not go on a field trip by yourself.
• Tell a responsible adult where you are going, and maintain that route.
• Know the area and its potential hazards, such as poisonous plants, deep water, and rapids.
• Dress for terrain and weather conditions (prepare for exposure to sun as well as to cold).
• Bring along a first-aid kit.
• Do not drink water or eat plants found in the wild.
• Use the buddy system; do not experiment outdoors alone.
FINISHING UP
• Thoroughly clean your work area and glassware.
• Be careful not to return chemicals or contaminated reagents to the wrong containers.
• Don’t dispose of materials in the sink unless instructed to do so.
• Wash your hands thoroughly.
• Clean up all residue, and containerize it for proper disposal.
• Dispose of all chemicals according to local, state, and federal laws.
BE SAFETY-CONSCIOUS AT ALL TIMES
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