Atmosphere

Question 1

(2) Iron reacts with oxygen to form iron oxide.
Iron wool was placed in the bottom of a wet test tube.

Explain why the water level in the test tube rose during the experiment.

Answer 1

the iron {reacts/combines}
with the oxygen (in the air)
/iron oxide formed(1)
• oxygen removed (from air)
(1)
• volume of gas decreases /
water rises to fill space (1)

Question 2

(2) The volume of air in the test tube at the start of the reaction was 10 cm3
.
Calculate the volume of gas that should be present in the test tube at the end of
the reaction.

Answer 2

% oxygen in air = 21 / % air remaining =
79 (1)
 volume of air remaining = 10 x 79 (1)
 100
 = 7.9 (cm3
)

Question 3

(1) Iron reacts with oxygen to form iron oxide.
Iron wool was placed in the bottom of a wet test tube.

Most of the gas remaining in the test tube at the end of the experiment would be

Answer 3

nitrogen

Question 4

(2) Explain how the use of fossil fuels affects the composition of the atmosphere.

Answer 4

burning/combustion (1)
• removes oxygen (1)
• adds carbon dioxide (1)
• adds water vapour (1)

Question 5

(1) Some time after the early atmosphere had been formed, oceans appeared on
the Earth’s surface.
State how these oceans were formed.

Answer 5

{water vapour / steam}

condensed/ changed to liquid

Question 6

(1) The amount of carbon dioxide in today’s atmosphere is much lower than that
in the early atmosphere.
State how the formation of the oceans caused this reduction

Answer 6

(carbon dioxide) dissolved/

absorbed / trapped

Question 7

(2) The amount of oxygen in todays atmosphere is much higher that the early atmosphere

Describe the process that caused this decrease

Answer 7

(primitive) plants (produce
oxygen) (1)
• (by) photosynthesis (1)

Question 8

(1) At the end of the experiment the apparatus was allowed to cool before the
final reading on the syringe was recorded.
This is because

Answer 8

the gas must be at room temperature when its volume is measured

Question 9

(1) The percentage of oxygen in air at room temperature is 21%.
John thought the answer to part (iii) was the percentage of oxygen in air and
was surprised that the value was too high.
John confirmed that he had not made an error when doing his experiment.
Suggest why the answer calculated in part (iii) is higher than John expected.

Answer 9

oxygen in air in test tube also
reacted /more than 32 cm3
 of air
because of air in test tube / air in
test tube will react but is not
measured

Question 10

(2) John’s results were
initial volume of gas in syringe = 32 cm3
final volume of gas in syringe = 24 cm3
Calculate the percentage decrease in the volume of gas originally in the
syringe.

Answer 10

volume gas used = 32-24 (1)
 = 8 (cm3
)
percentage = 32-24/32 x 100
(1) = 25 (%)

Question 11

(2) Explain why it is difficult to be precise about the composition of the Earth’s early
atmosphere.

Answer 11

nobody was there / OWTTE (1)
• there are no (written) records /
measurements (1)
• {different / conflicting} sources of
information (1)

Question 12

(1) As the Earth cooled, oceans formed.

How did this affect the composition of the atmosphere?

Answer 12

lowered the amount of {water vapour /
carbon dioxide} / oceans absorbed
carbon dioxide

Question 13

(2) The first plants appeared about 400 million years ago.
Explain how the growth of these plants affected the composition of the
atmosphere.

Answer 13

photosynthesis (in plants) (1)
• {decreased / absorbed} carbon
dioxide (1)
• {increased / released} oxygen (1)

Question 14

(1) What is the current approximate percentage of carbon dioxide in the Earth’s
atmosphere?

Answer 14

0.04

Question 15

(1) State another cause of increasing amounts of carbon dioxide in the atmosphere.

Answer 15

deforestation (1)
• volcanic activity (1)
• respiration (1)
• increase in temperature (1)

Question 16

(1) Which of these shows the relative amounts of carbon dioxide and oxygen in the
Earth’s early atmosphere?

Answer 16

large amount of carbon
dioxide and small amount of
oxygen

Question 17

(2) Explain how carbon dioxide is removed from the atmosphere

Answer 17

plants (1)
photosynthesis / take in carbon
dioxide and release oxygen (1)

Question 18

(2) Explain how carbon dioxide is released into the atmosphere

Answer 18

burning/ (complete)
combustion(1)
(fossil)
fuels/wood/rubbish/plastic etc
(1)
or
plants/animals/organisms (1)
respiration / gas exhaled /
breathing / decaying (1)

Question 19

(2) Describe the test to show that a gas is carbon dioxide.

Answer 19

limewater (1)
turns milky/cloudy/white
ecipitate (1)

Question 20

(3) Explain whether or not these graphs provide evidence that human activity is
causing the Earth’s temperature to rise.

Answer 20

concentration of carbon dioxide
increases (steadily) (1)
but the temperature
{fluctuates/increases and
decreases} (1)
dependent on at least 1
comment from a graph
any 1 from:
not all carbon dioxide is produced
by human activity (1)
none of the graphs refer to
human activity (1)
there is no proof that human
activity
causes the temperature to rise
(1)
other factors could cause the rise
in temperature (1)

Question 21

(1) The percentage of carbon dioxide in the Earth’s atmosphere today is

Answer 21

less than 0.5%

Question 22

(2) Explain what has caused the percentage of carbon dioxide to decrease.

Answer 22

dissolves /is absorbed (1)
• in the oceans (1)
• incorporated into marine
organisms (1)
• formed carbonate rocks
(1)
• increase in (green)
plants/plants start growing
• photosynthesis /plants
remove carbon dioxide

Question 23

(1) Carbon dioxide and other gases in the atmosphere help to keep the Earth
warm.
State how these gases keep the Earth warm

Answer 23

traps heat

Question 24

(2) Describe the test to show that a gas is oxygen.

Answer 24

glowing splint (1) M1
• relights (1) M2

Question 25

(2) When the magnesium flame went out, there was some magnesium left in the
basin.
When the apparatus had cooled, the water in the bell jar had risen.
Explain why the water level had risen

Answer 25

volume of gas in bell jar
decreases/water rises to
fill the space (1)
• oxygen is removed from
the air (1)

Question 26

(2) At the start of the experiment, the volume of the air in the bell jar was
1000 cm3
.
Assume that 21% of the air by volume is oxygen.
Calculate the volume of gas that was present in the bell jar at the end of the
experiment.

Answer 26

(amount of gases remaining) 79% (1)
(volume remaining) = 1000 x 79 (1)
                                       100
 = 790 (cm3
)