Chemistry Reference
In-Depth Information
Chemical reactions
●
Additional questions
1
Explain the following statements.
a
A car exhaust pipe will rust much faster if the car
is in constant use.
b
Vegetables cook faster when they are chopped
up.
c
Industrial processes become more economically
viable if a catalyst can be found for the reactions
involved.
d
In fireworks it is usual for the ingredients to be
powdered.
e
Tomatoes ripen faster in a greenhouse.
f
The reaction between zinc and dilute
hydrochloric acid is slower than the reaction
between zinc and concentrated hydrochloric
acid.
2
A student performed two experiments to establish
how effective manganese(
iv
) oxide was as a catalyst
for the decomposition of hydrogen peroxide.
The results below were obtained by carrying out
these experiments with two different quantities
of manganese(
iv
) oxide. The volume of the gas
produced was recorded against time.
3 a
Which of the following reaction mixtures
will produce hydrogen more quickly at room
temperature?
(iii)
zinc granules + dilute nitric acid
(iii)
zinc powder + dilute nitric acid
b
Give an explanation of your answer to
a
.
c
Suggest two other methods by which the speed
of this reaction can be altered.
4
A flask containing dilute hydrochloric acid was
placed on a digital balance. An excess of limestone
chippings was added to this acid, a plug of cotton
wool was placed in the neck of the flask and
the initial mass was recorded. The mass of the
apparatus was recorded every two minutes. At
the end of the experiment the loss in mass of the
apparatus was calculated and the following results
were obtained.
Time/min
0
2
4
6
8
10
12
14
16
Loss in mass/g
0
2.1
3.0
3.1
3.6
3.8
4.0
4.0
4.0
a
Plot the results of the experiment.
b
Which of the results would appear to be
incorrect? Explain your answer.
c
Write a balanced chemical equation to represent
the reaction taking place.
d
Why did the mass of the flask and its contents
decrease?
e
Why was the plug of cotton wool used?
f
How does the rate of reaction change during
this reaction? Explain this using particle theory.
g
How long did the reaction last?
h
How long did it take for half of the reaction to
occur?
5 a
What is a catalyst?
b
List the properties of catalysts.
c
Name the catalyst used in the following
processes:
(iii)
the Contact process
(iii)
the Haber process
(iii)
the hydrogenation of unsaturated fats.
d
Which series of metallic elements in the Periodic
Table (p. 136) do the catalysts you have named
in
c
belong to?
e
What are the conditions used in the industrial
processes named in
c
? The following references
will help you: Chapters 11, 12 and 14.
Time/s
0
30
60
90
120
150
180
210
Volume for 0.3 g/cm
3
0
29
55
79
98
118
133
146
Volume for 0.5 g/cm
3
0
45
84
118
145
162
174
182
a
Draw a diagram of the apparatus you could use
to carry out these experiments.
b
Plot a graph of the results.
c
Is the manganese(
iv
) oxide acting as a catalyst in
this reaction? Explain your answer.
d (i)
At which stage does the reaction proceed
most quickly?
(iii)
How can you tell this from your graph?
(iii)
In terms of particles, explain why the
reaction is quickest at the point you have
chosen in
(iii)
.
e
Why does the slope of the graph become less
steep as the reaction proceeds?
f
What volume of gas has been produced when
using 0.3 g of manganese(
iv
) oxide after 50 s?
g
How long did it take for 60 cm
3
of gas to be
produced when the experiment was carried out
using 0.5 g of the manganese(
iv
) oxide?
h
Write a balanced chemical equation for the
decomposition of hydrogen peroxide.
