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How is a mixture Cifferent
from a compound
Sometimes two or more substances are mixed together.
They do not combine chemically. They do not make a compound. They make a mixture. The substances €ue physicolly
combined. None of the substances in the mixture have been
changed chemically. No chemical reaction has taken place. No
new substances have been formed.
Vegetable soup is an example of a mixture. So is salt and
sand mixed together. You can still tell one part from another.
How can we tell the difference between a compound and
a mixture? Here are some clues:
MIXTURE
COMPOUND
The parts of a mixture do
not change their properties.
The elements that make up
compound lose their
properties. The new
compound has its own
properties.
A mixture may have ony
omount of each of its parts.
A compound must always
have a porticulor omount
of one element for a given
a
amount of other elements.
r40
Energy is not taken in or
given off when a mixture is
made or separated.
Energy is always taken in or
given off when a compound
is broken up or put together.
A mixture can be seporoted
by physical means. For
A compound can only be
seporoted with a chemicai
example, a strainer can
separate some mixtures.
reaction. For example,
electricity can cause some
chemical reactions.
li
ABOUT MIXTURES
A mixture can have many kinds of matter.
It can have
elements only
compounds only
D. An example of a mixture
The salt and pepper are just close
together. They do not react together. Properties do not change. The salt is still salt.
The pepper is still pepper. No new products are formed.
=
It makes no difference how much
pepper or salt there is. No exact amounts
elements and
compounds
C.
B.
A.
t
or
is salt with pepper'
are needed. Energy is not taken
in or given
off by the molecules of the salt or the
pepper.
Salt is a comPound. PePPer is a
compound. Salt with pepper is a mixture
made up of two comPounds.
747
TRUE OR Write T on the line next to the number if the sentence is true.
.cALSE Write F if the sentence is false.
1.
A mixture has exact amounts.
2.
A compound has exact amounts.
3.
The parts of a mixture keep their properties.
4.
The elements of a compound keep their properties.
b.
We need energy to make or break up a compound.
6.
Hydrogen is a compound.
Water is a compound.
B.
We need a chemical reaction to separate a compound.
9.
Electricity can separate some compounds.
10.
Heat can change water to oxygen and hydrogen.
iron filings
powdered yellow sulfur
test tube and holder
Bunsen burner
magnet
piece of paper
teaspoon
742
*+t
A.
B.
How To Do The Exneri;'ileni. -rari
A. 1.
.
Place a teaspoon of the sulfur on a piece of paper.
2.
Add about % teaspoon of iron filings.
3.
Mix them together.
B. 1.
Hold the magnet in the mixture. Move it around.
2, Lift the magnet.
iJt
I rlL
7.
Could you tell the sulfur from the iron before using the magnet?
2.
The magnet lifted
3.
The magnet did not
4,
Have you separated the iron from the sulfur?
D.
Did the properties of the iron change?
6.
Did the properties of the sulfur change?
,h"
lift
;;i*;:ffi;
the
iron. sulfur
Was a new product formed?
8.
Did a chemical reaction take place?
9.
Iron filings and sulfur together make
10.
A chemical equation
iron mixes with sulfur.
a
compound. mixture
be written to show what happens when
can, cannot
143
How
ro Do the Experiment. part II
O
D.
A.
1.
Remove the iron filings from the
magnet. Mix them in with the
sulfur.
2.
Pour the mixture into the test
tube.
3.
Heat the test tube over the Bunsen burner until the sulfur melts.
Remove the test tube from the
flame.
Let the tube cool. Cover the tube
with a cloth. Then break it by
carefully tapping the bottom of
the test tube with a hammer.
6.
B.
t. Put the magnet on the
2.
744
Remove the cloth. Examine the
substance that was in the test
tube.
Lift the magnet.
substance.
@
@
E
?
t:
lVhat You Learned
1.
Could you tell the suifur from the iron after they were heated together?
2, Did the magnet lift the iron filings?
3. Did the properties of the iron change?
4. Did the properties of the sulfur change?
5. Was a new product formed?
6. Did a chemical reaction take place?
7.Sulfurandironfilingsheatedtogethermake"@.
8.
The equation below shows what happens when iron and sulfur are heated together.
Fe+S --'
FeS
Take a guess-the compound made from iron and sulfur is called a) iron oxide.
b) iron sulfide. c) sulfur dioxide. fUnderline the correct onswer')
.ilxTi ---: '--'?
. _ ".Ll'
-
The chart below lists some terms and phrases that describe mixtures and compounds. Which ones describe mixtures? Which
describe compounds? Put a check ["'] in the space to show your
choice.
Mixture
1.
2.
Compound
properties change
properties do not change
_t: glct
amoyyts
4. no exact amounts
5. energy always taken in
or given off
6. energy not taken in or
giv n off
7. separated by chemical
means
8. separated by physical
means
9. rvhat you have in your
pocket or bag
10. iron sulfide
145
THRCT,V In each of the following sets of terms,
O|,iE OL;T belong. Circle that term.
1. mixture comPound water
salt
2. mixture . compound
pepper
3.
exact
amounts
salt with
no exact amounts
one of the terms does not
sand with water
compound
water
amounts mixture salt with pepper
5. properties change properties do not change chemical change
4.
exact
amounts
hydrogen exPlodes
146
no exact