Lab 7-1
Identifying Bond Types
Names ____________________________________________________ Date _______________
Objective
The purpose of this investigation is to determine which types of bonds are present in some
common materials by examining their electrical conductivities.
Materials
Baking soda
Brass (or some other metal)
Cola soft drink
Copper metal (wire or sheet) Orange drink mix (e.g., TangTM) Sugar
Table salt (NaCl)
Vegetable oil
Water (distilled)
Equipment
Beaker (250 mL)
Multimeter
Tablespoon
Introduction
You have learned from your study of chemical bonds that the type of bond often determines
the physical properties of a material as well as its chemical properties. This fact was
demonstrated in Investigation 7, "Metals and Nonmetals,” where you compared appearance,
electrical and thermal conductivity, and malleability of several different substances. You found
that metals often have a similar appearance and good conductive characteristics, but the
appearance of solid ionic and covalent compounds can vary greatly, and they generally conduct
electricity poorly. The conductivity of the various types of bonds can be explained as follows:
Metals. Electricity is conducted through a substance by electrons or charged particles (ions)
that are free to move around. The valence electrons of metals, whether in the solid or liquid
(melted) state, are very mobile since they are not strongly attracted to any particular atom. This is
a key principle of metallic bonding. Metals, therefore, conduct electricity in any state.
Ionic compounds. Ionic solids contain charged particles, but the crystal structure holds the
ions in a fixed position. Since the charged particles cannot move, dry solid ionic compounds will
not conduct electricity. However, if the ionic solid can dissolve in water or if the solid is melted,
the charged particles separate from each other (dissociate) and become free to move.
Consequently, an ionic compound dissolved in water or in the molten state will conduct
electricity. Though poly atomic ions (HC03-, for example) are held together with covalent bonds,
the ions still carry charges and their solutions will conduct electricity.
Covalent compounds. Covalent compounds in an un-ionized state have neither free electrons
nor charged particles and will not conduct electricity. Most covalent compounds will not form a
solution with water while some are only poorly soluble. Other covalent compounds such as sugar
are readily soluble in water. A few covalent compounds ionize in water, and these will conduct
electricity as in the case of ionic compounds.
Page 1 of 10
covalent compounds will not form a solution with water while some are only
poorly soluble. Other covalent compounds such as sugar are readily soluble in
water. A few covalent compounds ionize in water, and these will conduct
electricity as in the case of ionic compounds.
If you were given an unknown solid, how could you determine with fair
confidence
if unknown
it contained
metallic,
ionic, you
or covalent
In this
If you were
given an
solid,
how could
determinebonds?
with fair
confidence if it
investigation,
will use bonds?
the property
electrical conductivity
contained metallic,
ionic, you
or covalent
In thisofinvestigation,
you will to
usehelp
the property of
evaluate thetokinds
bonds inthe
several
electrical conductivity
helpof
evaluate
kindssubstances.
of bonds in several substances.
The table
following
table summarizes
the electrical
propelties
of compounds
The following
summarizes
the electrical
properties
of compounds
containing the
containing
the different types of bonds.
different types
of bonds.
Bonding Type
Metallic
Ionic
State
Conduction
Solid metal
Yes
Molten metal
Yes
Crystalline solid
No
Solution (water)
Yes
Molten
Yes
Questions
Solid
Name ___________________________
Hour______
Date'___________
No
Read Covalent
the entire investigation.
prior to
Liquid Answer the following questions
No
class on a separate sheet of paper. Use complete sentences.
Solution (water)
No (possibly yes)
1. What test will we be using in this investigation to determine the type
of bond?
2. Why do metals conduct electricity?
Pre~Laboratory Questions
3. Under
what conditions
compounds
conduct
electricity?
Read the entire
investigation.
Answer do
theionic
following
questions
prior
to class on a separate
Explain
why.
sheet of paper. Use complete sentences.
What test will we4.beWhy
using
in this investigation to determine the type of bond?
do covalent compounds not conduct electricity easily?
Why do metals conduct electricity?
5. Is it do
possible
determine the
type of
bond in a substance
by using
Under what conditions
ionic to
compounds
conduct
electricity?
Explain why.
conductivity
alone?
Why do covalent compounds not conduct electricity easily?
Is it possible to determine
the type of bond in a substance by using conductivity alone?
6. State the research question.
State the research question.
@
7. State
hypothesis
and predict of
thethe
conductivity
the following
State your hypothesis
andyour
predict
the conductivity
followingofmaterials,
given their
o
o
materials, given their composition.
composition.
I\)
104
Substance
Composition
Baking soda
Brass
Copper
Cola
Orange drink mix
Sugar
Table salt
Vegetable oil
Water (distilled)
NaHC0 3
Cu, Zn alloy
Cu
primarily C, 0, and H compounds
primarily C, 0, and H compounds
C, 0, and H compound
NaCl
primarily C, 0, and H compounds
H 20
Page 2 of 10
:i
!l
Chapter 8
Procedures
1. Obtain the multimeter. Touch the two probes together to make sure that the meter works. If it
doesn't, check all of the electrical connections.
2. Test the copper and the brass for conductivity by touching both probes to the surface of the
solid. Record your results in the data table.
1. Note: Be sure to thoroughly clean and dry the probes and the beaker after each of the
following liquid tests.
3. Test the four liquids (vegetable oil, cola, distilled water, and tap water) for conductivity, one
at.a time. Pour approximately 150 mL of the liquid into the 250 mL beaker. Test for
conductivity by placing the probes in the liquid (do not let the probes touch each other).
Record your results in the data table.
3
4. Put 30 cm (2 tablespoons) of baking soda in the dry beaker. Test the powder for conductivity
by placing the probes in the material. Do not let the probes touch each other or the bottom
of the beaker. Add 150 mL of distilled water to the dry material in the beaker and stir. After
the baking soda is dissolved, test again for conductivity by placing the probes in the
solution. Record your results for both the dry and the dissolved baking soda in the data
table.
5. Repeat step 4 using table salt, sugar, and the orange drink mix. Record your results for both
dry and dissolved materials in the data table.
6. In the third column write M if you believe metallic bonds are present, I if ionic, and C if
covalent. If the test is inconclusive, write a question mark.
Results
Data Table: Properties of Compounds
Compound
Conducts? (Y/N)
Magnesium
Copper
Cola
Vegetable oil
Distilled water
Tap water
Baking soda powder
Dissolved powder
Table salt crystals
Salt water solution
Sugar crystals
Sugar water solution
Orange drink mix (dry)
Orange drink (liquid)
Page 3 of 10
Bond Type (I, C, M)
Discussion Questions
1. Why do ionic compounds not conduct electricity when they are in the crystalline solid state?
______________________________________________________________________________
______________________________________________________________________________
2. Fill in the following blanks with metals or nonmetals
a. Metallic bonds form between two elements that are _______
b. Ionic bonds form between _____ and _____
c. Covalent bonds form between two ______
3. Predict the type of bond in each of the following compounds.
a: CO2
b. MgCl2
c. LiCl
d. S02
e. Ni-Cu alloy
4. Suppose that during one of the tests the light bulb did not light up and you concluded that the
material had covalent bonds. If you had not performed the bulb check at the beginning, how sure
could you be of your results?
______________________________________________________________________________
______________________________________________________________________________
5. What does this tell you about the necessity of controls in a scientific experiment?
______________________________________________________________________________
______________________________________________________________________________
Page 4 of 10
Lab 7-2
pH of Common Solutions
Objectives
The purpose of this exercise is to
Observe the use of various pH indicators and methods.
Determine the pH of several common substances.
Materials
Ammonia, household
Clear soda
Cola
Dishwashing detergent
HCI solution
Lemon juice
Litmus paper
Milk
NaOH solution
pHydrion™ paper or equivalent
Vinegar
Other household items (optional)
Bromothymol blue indicator (optional)
Phenolphthalein indicator (optional)
Equipment
Beakers, 50 mL
Eyedroppers
Test tubes
Test tube racks
Introduction
The pH of solutions can be determined subjectively by acid-base indicators. Recall from
your textbook that these are organic substances that change color in the presence of an acid or a
base. Litmus is an indicator extracted from a certain kind of lichen, a mossy substance that grows
on rocks and trees. In its indicator form, litmus is red from a pH of 0.0 to 4.5 (acid) and blue
from 8.3 to 14.0 (base). Between a pH of 4.5 and 8.3, the color of the chemical is intermediate
between red and blue and is not a good indicator of the pH. Litmus is used to determine if a
substance is an acid or a base, but it cannot provide numerical pH values. Other pH indicators,
such as phenolphthalein or bromothymol blue, change color at different, specific pH values.
They can tell you whether the pH is above or below their specific turning points, but, like litmus,
they cannot give you a specific pH determination. Some substances tum many colors over a wide
range of pH values. These indicators are the most useful because they can determine not only
whether a solution is an acid or a base, but they can also indicate the numerical pH of the
solution. This kind of substance is called a universal indicator. pHydrion paper is one such
Page 5 of 10
indicator. The numerical pH ) value of the tested solution is determined by comparing the color of
the 5 universal indicator in the solution with a standardized color chart that is provided by the
manufacturer.
~
E. Phenolphthalein Station (Optional)
Add one dropper full of NaOH solution to one test tube and a dropper full of Hel solution to a
second test tube.
Place two drops of phenolphthalein indicator into each of the test tubes.
Record the resulting colors in Table 2.
Rinse the tubes with water and place them upside down in the test tube rack.
Results
Table 1: pH of Common Solutions
Station
Solution
Litmus
Paper
Universal
indicator
Acid or
Base?
Station
A
I
B
J
C
K
D
L
E
M
F
N
G
O
H
P
Solution
Litmus
Paper
Universal
indicator
Acid or
Base?
Discussion Questions
1. What was the most basic solution tested? Most acidic? ______________________________
___________________________________________________________________________
2. Bases produce an excess of _______ ions.
3. Acids produce an excess of ________ ions.
4. At a pH of 7, the concentrations of Hp+ and OH-ions are [different] [equal] (circle one),
5. The numbers on the pH scale go from ____ to ____
6. The numbers for the pH scale indicate the concentration of what ions? _____
7. Substances that are acidic taste [sour] [bitter]. Farmers in times past have tasted the soil to
determine its quality. If the soil tasted slightly sour, they would say that the soil needed to be
Page 6 of 10
sweetened. This was usually done by adding ashes or, today, by adding lime. This simple
taste test indicated that the soil needed to be made more [acidic] [basic].
8. It can be observed that many preferred food items tend to be [acidic] [basic] and cleaning
items tend to be [acidic] [basic].
Page 7 of 10
Lab 7-3
Chemical and Physical Changes
Objectives
The purposes of this investigation are to
Learn the difference between chemical and physical changes.
Learn the difference between evidence a,nd proof that a chemical change has occurred.
Materials
Aluminum foil
Ammonia
Baking soda
Epsom salts
Sugar
Table salt
Vinegar
Equipment
Beaker (250 mL)
Beakers (100 mL), 2
Bunsen burner
Bunsen burner lighter
Graduated cylinder (100 mL)
Large rubber band
Teaspoon
Tripod
Wire gauze
Introduction
Chemistry is primarily the study of chemical and physical changes of matter, while
physics focuses on physical processes involving matter. A physical change occurs when a
substance simply changes shape, form, or state (gas, liquid, or solid)-its identity is not altered.
Examples of physical changes include boiling, evaporation, melting, bending, tearing, and
dissolving. A chemical change results when a new substance is formed that is different from the
original material(s). The research question is "Is it possible to distinguish between physical and
chemical changes?" Physical changes can frequently be easily "undone" or reversed. Ice can be
melted and refrozen. Clay can be formed into a different shape. However, chemical changes are
often very difficult to reverse. The appealing of a new and different substance is proof that a
chemical change has occurred. There are some common evidences that often accompany
chemical reactions. They are summarized as follows:
Evidence
A solid separates from a liquid.
A gas is produced.
The colors of the chemicals change permanently.
The temperature of the substance changes.
Light or sound is produced.
Page 8 of 10
Proof
The appearance of a new and different substance is established by analytical tests.
These evidences alone do not prove that a chemical change has occurred. Some of these also
accompany certain physical changes. For example, boiling water produces gas and sound during
a phase change --a physical change. The appearance of a solid crystalline salt in a slowly
evaporating salt solution is another example of a physical change. In order to prove that a
chemical change has taken place, the suspected new substance must be chemically analyzed in
the laboratory to determine its identity.
Pre-Laboratory Questions
Read the entire investigation. Answer the following questions. Use complete sentences.
1. What is a physical change?
2. What is a chemical change?
3. State the research question.
4. For your hypothesis, state whether the following procedures will result in a chemical or a
physical change?
Burning sugar
Mixing salt and water
Mixing baking soda and vinegar
Stretching a rubber band
Mixing red cabbage juice and ammonia
Mixing Epsom salts and ammonia
Results
Burning
sugar
Mixing salt
and water
Baking
soda and
vinegar
Stretching a
rubber band
Page 9 of 10
Universal
indicator
and
ammonia
Epsom
salts and
ammonia
Universal
indicator
and vinegar
Discussion Questions
1. What is a physical change? ____________________________________________________
___________________________________________________________________________
___________________________________________________________________________
2. How would you prove that a chemical change has occurred? _________________________
___________________________________________________________________________
___________________________________________________________________________
3. What evidences may indicate that a chemical change has occurred? _____________________
___________________________________________________________________________
___________________________________________________________________________
4. Give an example from this exercise of a physical change that produced evidence associated
with chemical changes. _______________________________________________________
___________________________________________________________________________
___________________________________________________________________________
5. Identify the following as physical or chemical changes.
1. P C Water freezing into ice cubes
2. P C Coals burning in a BBQ
3. P C Meat cooking
4. P C A pencil being sharpened
5. P C Sugar dissolving in water
6. P C Gunpowder exploding
7. P C Paper being folded
8. P C Gasoline evaporating
9. P C Gasoline burning
Page 10 of 10