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An enzyme is a special
kind of catalyst. How
does it work?
Show Answer
Answer for 5 Points
It speeds up a specific
biochemical reaction.
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What must be true for a
substance to be recognized
as an element?
Show Answer
Answer for 5 Points
Be made up of only one
type of atom
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A student set up the apparatus
for electrolysis of water and
let it run for 5 minutes; she
collected 60 cm3 of hydrogen.
What volume of oxygen did
she collect?
Show Answer
Answer for 5 Points
30 cm3
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What is a
synthesis
reaction?
Show Answer
Answer for 5 Points
A chemical reaction that results in the
combination of two or more pure
substances to make a more complex pure
substance.
Example:
2H2 + O2  2H2O
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What is a
decomposition
reaction?
Show Answer
Answer for 5 Points
A chemical reaction that results in
the breaking down of pure
substance into two or more pure
substances
Example:
2H2O  2H2 + O2
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What is an
incomplete
reaction?
Show Answer
Answer for 10 Points
Neither of the reactants are
completely used up in the chemical
reaction.
Example:
2Cu + O2  2CuO
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What is a
complete
reaction?
Show Answer
Answer for 10 Points
One of reactants is completely
used up, causing the chemical
reaction to stop.
Example:
Zn + 2HCl  ZnCl2 + H2
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In the Synthesis of Water….
Volume
H2
Volume
O2
75 cm3
50 cm3
25 cm3
50 cm3
50 cm3
150 cm3
25 cm3
100 cm3
What’s
Left?
Show Answer
Answer for 10 Points
Volume
H2
Volume
O2
What’s
Left?
75 cm3
50 cm3
25 cm3
50 cm3
25 cm3 H2
25 cm3 O2
50 cm3
150 cm3
25 cm3
100 cm3
Nothing
25 cm3 O2
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Describe the Law of constant
Proportions-
Show Answer
Answer for 10 Points
When two substances combine to
form a compound, they always
combine in a constant proportion.
The ratio of the masses that react
remains constant, no matter how
much of the substances are
mixed. It is a Law of nature.
Back to Board
When doing Experiment 6.2, The
Decomposition of Water, a student began
with 100 cm3 of water in the apparatus. The
student collected 57 cm3 of hydrogen and 28
cm3 of oxygen. What fraction of the total
volume of water was decomposed?
3
3
Show Answer
Answer for 10 Points
4.1 x
-4
10
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What evidence do you have for
each of the following statements?
a. Zinc chloride is a pure
substance and not a mixture.
b. Water is a pure substance.
Show Answer
Answer for 15 Points
a.
The ratio (mass of zinc reacted)/(mass
of zinc chloride)is constant, regardless
of how much zinc is added to
hydrochloric acid
b.
Water has a definite melting point, so it
is not a mixture. When hydrogen and
oxygen are mixed in different ratios and
ignited, they combine in a fixed ratio
and form water.
Back to Board
A student heated a crucible containing 2.15
g of powdered copper until the mass of the
contents of the crucible became 2.42 g. The
black solid in the crucible was then placed
in hydrochloric acid, and 1.08 g of copper
remained undissolved in the acid. What is
the ratio of the mass of oxygen reacted to
the mass of copper reacted?
Show Answer
Answer for 15 Points
Mass of oxygen reacted= 0.27=0.25
Mass of copper reacted
1.07 g
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If two substances react to form a
compound, and only one of
them remains when the reaction is
overl is the reaction complete
or incomplete?
Show Answer
Answer for 15 Points
Complete Reaction
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A complete reaction takes place between Substance A
and Substance B. What will remain after the reaction?
(Select all the possible correct answers.)
A. Substance A and the product of the reaction only
B. Substance Band the product of the reaction only
C. Both Substance A and Substance B1 along with the
product of the reaction
D. Neither Substance A nor Substance B; all that will
be left is the product of the reaction
Show Answer
Answer for 15 Points
A,B,D
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An incomplete reaction takes place between
Substance A and Substance B. What will remain
after the reaction?
(Select all the possible correct answers.)
A. Substance A and the product of the reaction only
B. Substance Band the product of the reaction only
C. Both Substance A and Substance B, along with the
product of the reaction
D. Neither Substance A nor Substance B; all that will
be left is the product of the reaction
Show Answer
Answer for 15 Points
C
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Does the volume of hydrogen plus the
volume of oxygen collected in Experiment
6.2 equal the volume of water
decomposed?
Show Answer
Answer for 20 Points
No
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What is the combined mass of oxygen and
hydrogen that can be produced when 180 g of
water is decomposed by electrolysis?
Show Answer
Answer for 20 Points
The combined mass of
oxygen and hydrogen
would be same as the
mass of water
decomposed-180 g mass
is conserved
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If all the volume of hydrogen gas produced from a
180 g of water were burned in air to form water,
what mass of water would result?
Show Answer
Answer for 20 Points
The mass of water produced would be
same as the mass of the original
sample that was decomposed -180 g
Back to Board
Suppose that some zinc chloride
solution was left in the test
tube when the solution was poured
into the evaporating dish.
How would this affect your
calculation for the ratio of the mass
of zinc reacted to the mass of
chlorine reacted?
Show Answer
Answer for 20 Points
The amount of zinc chloride that is
evaporated to dryness would be less than it
should be. When mass of chlorine reacted is
found by subtracting the mass of zinc reacted
from the mass of zinc chloride produced, the
resulting mass of chlorine will be too small.
Since the mass of chlorine is in the
denominator of the ratio, this would increase
the ration of the mass of zinc reacted to the
mass of chlorine reacted.
Back to Board
a. How much chlorine will react with 5.00 g
of zinc to form zinc chloride?
b. How much zinc chloride will be
produced?
Show Answer
Answer for 20 Points
a. If the ratio of zinc to chlorine is
0.92, 5.00 g of zinc will react
5.00/0.92 =5.43 g of Chlorine
b. The mass of zinc chloride produced
is 5.00 g + 5.43 =10.43
Back to Board
Show Answer
Answer for 25 Points
Ratios b, c, d, f,and g
are constant
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In the electrolysis ofwater, which of the following
conditions affects the ratio of the volume of
hydrogen produced to the volume of oxygen
produced?
A. The time the apparatus was connected to the battery
B. The mass of water electrolyzed
C. The temperature of the water
D. The mass of sodium carbonate added to the water
E. None of the above
Show Answer
Answer for 25 Points
E. None of the above
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When water is electrolyzed, the volume of hydrogen
produced is twice the volume of oxygen produced.
The density of hydrogen is 8.4 x 10-5 g/cm3; the
density of oxygen is 1.3 x 10-3 g/cm3. On the basis of
these data, what is the value of this ratio?
Mass of hydrogen in a sample of water
Mass of oxygen in the same sample of water
Show Answer
Answer for 25 Points
-5
10
2 x 8.4 x
-3
1 x 1.3 x 10
Back to Board
Suppose you electrolyze water and obtain 40
cm3 of hydrogen and 20 cm3 of oxygen. Then
you mix these gases with an additional 10 cm3
of hydrogen and pass a spark through the
mixture. What happens?
Show Answer
Answer for 25 Points
Water will be formed ;
and 10cm3 of hydrogen
will be left over
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Suppose you pick up a rock in a park. Which
element is the rock most likely to contain?
Show Answer
Answer for 25 Points
Oxygen
Back to Board
Authored by
Jeff Ertzberger - 2004
University of North Carolina at Wilmington
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