Activity 1
Elements and Compounds
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GOALS
What Do You Think?
In this activity you will:
Matter is the name for all the “stuff” in the universe. Anything that
has mass and occupies space is called matter.
• Decompose water by
electrolysis into the two
elements from which it is
composed.
• Test the two elements to
determine their identities.
• Learn one way to determine
the chemical formula of a
material.
• Compare characteristic
properties of a material
to those of its constituent
elements.
• Represent materials with
chemical formulas using
numbers and the symbols of
elements.
• Practice safe laboratory
techniques with flames and
explosions.
• How many kinds of matter are there in the universe: 1, 10, 100,
1 000, 10 000, 100 000 or 1 000 000?
• What makes up matter?
The What Do You Think? questions are meant to get you thinking
about what you already know or think you know. Don’t worry about
being right or wrong. Discussing what you think you know is an
important step in learning.
Record your ideas in your Active Chemistry log. Be prepared to discuss
your responses with your small group and the class.
Investigate
1. Look around your classroom at the kinds of matter that make up
the things you see.
a) Make a list of 10 kinds of materials that make up the objects
you see. For example, you might list the wood in your pencil, or
the glass in the windows.
b) To understand the nature of matter, it helps to know if it is
simple or complex. Is the matter made from only one kind of
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material or is it a mixture of
various materials? Classify each
of the 10 materials you listed as
pure or mixtures.
c) For each material you thought
was a mixture, write your best
guess about what materials make
it up.
Safety goggles
and a lab apron
must be worn
at all times in a
chemistry lab.
2. Sometimes the materials that make
up a substance are not obvious.
Early scientists thought that water
was an element. In other words,
they thought that there was only one
kind of material in water. They had
not discovered a way of breaking it
down further. Water, however, can
be broken down further.
a) Carefully observe the
characteristic properties of
water. Record at least three
observations of water in your log.
3. Assemble the apparatus for
decomposing water as shown in the
diagram. Fill two test tubes with
water. Submerge them in the water
in the beaker and invert them. Make
sure you do not allow any air to
enter the test tubes. The ends of
electrical leads
electrolysis
apparatus
stainless steel
or platinum
electrodes
–
–
+
+
–
+
9-V
water containing
dissolved
sodium sulfate
9-V batteries
the wires should be stripped. Polish
them with steel wool. Insert the
ends of the wires into the test tubes.
Add about 1 to 2 mL of sodium
sulfate solution to the water in the
beaker.
4. Plug in the set of three 9-V batteries
in series or use a power supply. Let
the reaction run until a test tube is
half-full of gas. (Your teacher may
decide to have you stop the reaction
sooner.)
a) Note what happens when the
power is turned on. Record
your observations in your Active
Chemistry log.
b) How do the relative amounts
of gas formed in the test tubes
compare?
5. Disconnect the batteries or power
source. While inverted, place
stoppers in the test tubes and
remove them from the water.
a) What gas do you think is
contained in each test tube?
(Hint: You’ve probably heard that
water is H-2-O, written H2O.)
Record your prediction, and give
reasons for your prediction.
b) Observe the physical properties of
each gas. Record these properties
in your log.
6. Remove the stopper while the test
tube is inverted. Drain the water
and replace the stopper. You are
going to use a lighted wooden splint
to identify the gas in each test tube.
First, examine the test tube with
the smaller volume of gas. Light a
wooden splint. Blow out the flame,
but leave the splint glowing. Hold
the test tube with its mouth up.
Remove the stopper. Quickly bring
the glowing splint to the mouth of
the test tube.
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Activity 1 Elements and Compounds
water (H2O) decomposed into
hydrogen gas and oxygen gas.
a) How would you write an equation
to show this decomposition?
a) Observe what happens to
the splint and record your
observations.
b) What gas do you think was
produced in this test tube?
c) In your log record any additional
properties of the gas that you
discovered.
7. Next, examine the test tube that
contains the larger volume of gas.
Light a wooden splint. Keep the test
tube inverted. Remove the stopper.
Quickly bring the burning splint to
the mouth of the test tube.
a) Record your observations.
b) What gas do you think was
produced in this test tube?
c) In your log record any additional
properties of the gas that you
discovered.
8. Return the splints and equipment as
directed by your teacher. Clean up
your workstation.
9. You may have deduced that the
10. You may think of ways of using the
tests (glowing splint and burning
splint) as special effects in your
show. Your teacher will demonstrate
an additional way you can use
what you investigated to produce a
special effect. Your teacher will set
up a gas generator, similar to the
one shown in the diagram.
The test tube contains 10 mL of
6 M HCl (hydrochloric acid is
a compound of hydrogen and
chlorine) and 3 g of zinc.
Be certain that
the mouth of
the test tube is
pointed away
from everyone.
Clean up spills
immediately.
Wash your
hands and arms
thoroughly after
the activity.
Both the
teacher and the
students must
be shielded
during this part
of the activity.
a) What gas do you think is being
produced in the test tube?
Give a reason for your answer.
11. An egg has been emptied out. There
is a small hole in the top and another
in the bottom of the egg. The top
hole is taped. The bottom hole in
the egg will be placed over the gas
generator, and gas will be collected
in the egg for several minutes.
12. The egg will then be mounted in
an egg holder behind a shield. If
you have a video camera available,
be prepared to start recording.
Your teacher will remove the tape,
and light the top of the egg with
a burning splint. Begin recording
or observing the reaction until it
is over.
a) Record your observations in
your log.
b) If the gas in the egg was hydrogen
and air contains oxygen, what
substance do you think may have
been created in this process?
c) Write an equation that shows
how the two gases produced this
new substance.
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Chem Words
element: any material
that cannot be broken
down into simpler
materials.
THE STRUCTURE OF MATTER
In this investigation you used electricity to decompose water into two
gases. You learned that the gases were different because they reacted
differently to the burning and glowing splints. Since water is referred to
as H2O, a first guess would be that hydrogen (H) and oxygen (O) were
produced in the experiment. The test for hydrogen is a small explosion
when exposed to a burning splint. The test for oxygen is the re-ignition
of a glowing splint. If you look back on the results of the experiment,
you find that the volume of the hydrogen gas was twice as much as the
oxygen gas. There was twice as much hydrogen as oxygen; that’s where
the “2” comes from in the chemical formula H2O.
Hydrogen and oxygen are elements. An element is any material that
cannot be broken down into simpler materials by chemical means.
You are probably familiar with many elements like hydrogen, oxygen,
zinc, gold, or helium. Other elements like strontium and beryllium are
more exotic and less likely to be familiar to you. Every kind of matter
you observe in your everyday life is made up of the chemical elements.
There are only a little more than a hundred different kinds of chemical
elements. This is an amazing discovery of
chemistry — everything you observe in the
world is made of different combinations of a
hundred elements. Chemistry is the study of
the properties of these elements, how these
elements combine, the new properties of these
combinations, and the energy changes that result
from these combinations.
Elements are represented by symbols. The
periodic table shows that the
symbol used for each element is
one or two letters to represent
the name. It’s easier to write
O than to write oxygen. It’s
easier to write H than to write
hydrogen. The symbols come
from many different sources.
However, the same symbols
are used for each element in all
countries of the world.
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Activity 1 Elements and Compounds
When elements combine,
they form new substances
called compounds. These
compounds have entirely
new characteristics. It is like
combining the letters of the
alphabet to make words.
Twenty-six letters can be
combined to make thousands
of different words. Water is
an example of a compound.
A water molecule, H2O, is
composed of two atoms
of hydrogen and one atom
of oxygen. (For now, think
of an atom as the smallest
particle of an element and
a molecule as the smallest
unit of a compound.) In this
activity you used electricity
to decompose water into
its elements, hydrogen and
oxygen. This process is called
electrolysis. You observed
that oxygen gas made a
glowing splint burst into
flame, and that hydrogen gas
was explosive. However, to
extinguish a burning splint,
you could use liquid water.
The compound has very
different characteristics from
the elements from which it
is made.
Chem Words
Symbols for Some Elements
Name of element
aluminum
bromine
calcium
carbon
chlorine
copper
gold
helium
hydrogen
iodine
iron
lead
magnesium
mercury
neon
nickel
nitrogen
oxygen
phosphorus
potassium
silicon
sodium
sulfur
tin
zinc
Symbol
Al
Br
Ca
C
Cl
Cu
Au
He
H
I
Fe
Pb
Mg
Hg
Ne
Ni
N
O
P
K
Si
Na
S
Sn
Zn
compound: a substance
that consists of two or
more elements bonded
together in definite
proportion.
electrolysis: the
conduction of electricity
through a solution
(that contains ions) or a
molten (ionic) substance
that results in a chemical
change.
chemical formula: the
combination of the
symbols of the elements
in a definite numerical
proportion used to
represent molecules,
compounds, radicals,
ions, etc.
Compounds are represented by chemical formulas. A chemical
formula shows the symbols of the elements that are combined to make
the compound. If there is more than one atom of an element, a subscript
is added after the symbol indicating how many atoms of that element
there are. For example, as you discovered in this activity, the chemical
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Examples of Some Chemical Formulas
Compound
Common name
Chemical formula
calcium carbonate
chalk
CaCO3
carbon dioxide
dry ice
CO2
hydrochloric acid
muriatic acid
HCl
hydrogen sulfide
rotten-egg gas
H2S
sodium hydrogen carbonate
(or sodium bicarbonate)
baking soda
NaHCO3
sodium chloride
table salt
NaCl
sodium nitrate
fertilizer
NaNO3
sulfuric acid
battery acid
H2SO4
formula for water is
H2O. Two hydrogen
atoms combine with
one oxygen atom
to produce one
molecule of water.
You could call H2O
dihydrogen monoxide
but you use the
common name water.
In chemistry, there
are common names
for some familiar
chemical compounds.
From the table of chemical formulas, you can see that carbon
dioxide (CO2) is a compound of carbon and oxygen. There
are two atoms of oxygen for every atom of carbon. Sodium
hydrogen carbonate or sodium bicarbonate (NaHCO3) is a
compound of sodium, hydrogen, carbon, and oxygen. There are
three atoms of oxygen for every atom of the other elements.
Also, there are a total of three atoms in the carbon dioxide
formula and a total of six atoms in sodium hydrogen carbonate.
Many elements appear as single atoms in nature. There are
seven common elements that exist in diatomic form. They are:
Hydrogen (H2), Oxygen (O2), Nitrogen (N2), Fluorine (F2),
Chlorine (Cl2), Bromine (Br2), and Iodine (I2).
For example, hydrogen may be found as a single atom in a compound
like HCl and oxygen may be found as a single atom in H2O. When
hydrogen is not combined with any other element, it always appears as
H2, two hydrogen atoms combined together.
You can write an equation that summarizes the electrolysis of water:
H2O(I) + energy → H2(g) + O2(g)
Notice that the letters “g” and “l” are used. The “g” means gaseous
state and the “l” means liquid state. Also notice that the elements are
written in their diatomic form. Conservation of mass and elements
states that the number of hydrogen atoms must be equal before and
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Activity 1 Elements and Compounds
after the reaction. In addition, the number of oxygen atoms must be
equal before and after the reaction. In the previous equation, you have
one oxygen atom before the reaction and two oxygen atoms after the
equation. You can fix this problem by “balancing the equation.”
2H2O(I) + energy → 2H2(g) + O2(g)
You now have 2 water molecules before the reaction (4 hydrogens
and 2 oxygens). You also have 4 hydrogens and 2 oxygens after the
reaction. You balanced the equation because you know that mass and
elements must be conserved. By balancing the equation, you found that
in electrolysis 2 water molecules decompose into 2 hydrogen molecules
and 1 oxygen molecule. This is why you saw that there was twice as
much hydrogen in one test tube than oxygen in the other test tube.
To generate the gas to fill the empty eggshell in this activity (the teacher
demonstration), zinc was placed in hydrochloric acid. Zinc is an element.
Hydrochloric acid (HCl) is a compound of hydrogen and chlorine.
The reaction of the zinc and hydrochloric acid created a gas. Given
the explosion you observed, you can guess that the gas produced was
hydrogen. The hydrogen gas came from the hydrogen in the hydrochloric
acid. You can write this reaction as an equation:
HCl(aq) + Zn(s) → ZnCl2(aq) + H2(g)
The sub letter “s” means that the substance is in the solid state. The sub
letters “aq” mean that the substance (HCl) is dissolved in water. The
zinc combined with the chlorine and hydrogen was released. Once again,
conservation of mass and elements requires you to balance the equation:
2HCl(aq) + Zn(s) → ZnCl2(aq) + H2(g)
There’s much more to the structure of matter than you can discover
in just one activity. However, this activity may have raised some new
questions in your mind. For example:
• Can all compounds be decomposed into their elements?
• What techniques can be used to decompose compounds?
• What are elements made of?
• What are atoms?
• What are molecules?
These questions and many more are answered in other Active Chemistry
activities.
Checking Up
1. In your own words,
explain the difference
between an element
and a compound.
2. Why are symbols useful
in describing chemical
elements?
3. What are the symbols
for the following
elements: carbon,
copper, gold, and
helium?
4. What information does
a chemical formula of
a compound provide?
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What Do You Think Now?
At the beginning of the activity you were asked:
• How many kinds of matter are there in the universe: 1, 10, 100, 1 000, 10 000,
100 000 or 1 000 000?
• What makes up matter?
Matter is all of the stuff in the universe and it can either be a compound or an
element. How many kinds of elements are there? How many kinds of compounds
are there? Give an example of each.
What does it mean?
Chemistry explains a macroscopic phenomenon (what you observe)
with a description of what happens at the nanoscopic level (atoms
and molecules) using symbolic structures as a way to communicate.
Complete the chart below in your Active Chemistry log.
MACRO
NANO
Describe what you observed in
the decomposition of water and
while generating hydrogen.
In words, describe what is
happening to the compounds
(electrolysis of water and zinc
reacting with hydrochloric
acid) during the two separate
experiments in this activity.
SYMBOLIC
Draw a picture that represents
the decomposition of water
(H2O) into hydrogen (H2) and
oxygen (O2). Beneath the picture,
write the chemical formulas
that are used to symbolically
represent the elements.
How do you know?
Water is often referred to as H2O. What evidence do you have that
water is composed of hydrogen and oxygen?
Why do you believe?
Individual elements will behave one way when they are alone and
another way when they are combined with other elements. Create an
analogy that is true from your life to show how a compound can behave
differently from its parts.
Why should you care?
You will be writing a movie scene for your challenge in this unit. Write a
short scene using an egg-explosion and describe how the hydrogen was
generated.
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Activity 1 Elements and Compounds
Reflecting on the Activity and the Challenge
Part of the problem you are facing in creating a special effect is understanding what
matter is made of and how it can change. In this activity you broke a chemical
compound down into its component elements using electrolysis. In another part
of the activity a compound was made from chemical elements through a fast and
noisy reaction. There are only about one hundred elements, but there are far more
than a million compounds. You should begin thinking of ways in which some of the
reactions you observe could be made to appear more dramatic on screen, without
making them any larger in real life. You can now use the concepts of elements and
compounds to provide the chemistry description of what is occurring.
1. The table shown contains several common compounds that
are probably familiar to you.
For each compound:
Common name
table sugar
marble
a) List the names of the elements present.
natural gas
b) State the number of atoms of each element present.
c) Give the total number of atoms present in each compound.
rubbing alcohol
glass
2. Write a chemical formula for nitrous oxide (laughing gas)
that is made up of two atoms of nitrogen and one atom of
oxygen.
Formula
C12H22O11
CaCO3
CH4
C3H8O
SiO2
3. Choose one compound from the table in Question 1.
a) Investigate and record the properties of each element in the compound.
b) Explain how the property of the compound is different from the property of
each element.
4. Preparing for the Chapter Challenge
In a short paragraph, summarize the difference between an element and a
compound and describe how the properties of a compound can be very different
from the properties of the elements that make it up. Explain why knowing these
differences is important when designing special effects for a movie set.
Inquiring Further
How is electrolysis used in industry?
Use the reference materials available to you to explore how electrolysis is used in
industry to produce hydrogen gas and other elements from compounds.
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