CHAPTER 24 EXPLORING EARTH’S OCEANS
Name:
QUESTIONS
24.2 Scuba science
1. A sample of nitrogen occupies 90.0 mL at 40.0 °C and a pressure of 80.0 kPa. What
pressure would be needed to reduce the volume to 30.0 mL at 40.0 °C?
2. What would be the volume of a sample of air in a syringe at a pressure of 45.0 kPa if the
same sample occupied 140 mL at 100 kPa?
3. A balloon has a volume of 1.5 L at 1 atm pressure and 24 °C. Calculate its volume if it is
taken outside and the temperature is –5 °C.
4. An 80 L scuba tank contains 2.5 mol of nitrogen. The gas is divided equally into two
smaller cylinders, each having a volume of 40 L. All cylinders are at the same temperature
and pressure.
(a)
What amount, in moles, of nitrogen is in each cylinder?
(b)
What is the mass of nitrogen in each cylinder?
24.3 Pressure, temperature and volume
5. A cylinder of compressed oxygen at 25.0 °C has a volume of 50.0 L and stores the oxygen
at 14 atm. If the cylinder needs to be cooled until the pressure falls to 10.0 atm, to what
temperature must it be cooled?
6. A fitter and turner needs a supply of 450 L of oxygen at 145 kPa pressure and a
temperature of about 30 °C for a day’s work. To what pressure must her 60.0 L tank be
filled at 12.5 °C?
7. The observation that molar volumes are not exactly the same for all gases suggests that
they do not behave exactly according to the kinetic molecular theory. Re-examine the
points of this theory and identify any that may account for the reality of gas behaviour.
8. Calculate the amount of nitrogen gas in 3.4 L at SLC.
9. 1.50 L of H2S was collected at STP. Calculate the mass of hydrogen sulfide.
© John Wiley & Sons Australia, Ltd
1
QUEENSLAND CHEMISTRY
10. Calculate the amount of gas in a 55 L cylinder if the pressure is 360 000 Pa at 25 °C.
11. Calculate the mass of helium in a 100 L balloon at a pressure of 0.4 atm and a temperature
of –5 °C.
12. What volume of ethyne gas would be produced at 25 °C and 1 atm, along with calcium
hydroxide Ca(OH)2, from 5 g of water reacting with excess carbon carbide (CaC2)?
13. Calculate the volume of carbon dioxide at SLC that is required to produce 1.0 g of glucose
(C6H12O6) by photosynthesis.
Review questions
1. When a diver breathes in all she can at sea level (atmospheric pressure = 101 kPa), her
lung capacity is 5.85 L. Calculate the volume of her lungs when she holds her breath and
dives down to where the pressure is doubled. Assume the temperature is the same in the
water as the air temperature.
2. A 100 mL capacity syringe contains 87 mL of air measured at 101.3 kPa and 25 °C. To
what temperature could the air be raised before its volume exceeded the syringe’s
capacity?
3. Two cylinders of oxygen are at the same temperature and pressure. The first has a volume
of 20 000 L. A second cylinder has a volume of 500 L and contains 35 mol of oxygen.
Calculate the mass of oxygen that must be in the first cylinder.
4. A container of gas has a volume of 15.5 L and is at a pressure of 2.00 atm at 30.0 °C.
What size container would be needed for the same amount of gas at a pressure of 4.50 atm
at 22.5 °C?
5. Calculate the volume occupied by 1.8 mol of hydrogen at STP.
6. 0.96 L of a gas collected at STP has a mass of 5.40 g. Find the molar mass of the gas.
7. What is the pressure in a 10.0 L flask at 15 °C if it contains 0.30 mol of nitrogen gas?
8. You want to produce 2 L of hydrogen gas to fill a balloon at atmospheric pressure and
20 °C from the reaction of hydrochloric acid with magnesium. What mass of magnesium
would be needed?
9. A sealed gas syringe has its volume doubled by drawing out the plunger. Meanwhile, its
temperature is raised from 10 to 20 °C. How does the new pressure compare to the old?
A
It is the same.
B
It is double.
C
It is half.
D
It is less than half.
10. The pressure on a fixed mass of gas is doubled and at the same time the absolute
© John Wiley & Sons Australia, Ltd
2
QUEENSLAND CHEMISTRY
temperature is doubled. The final volume is:
A
one-quarter the original volume.
B
the same as the original volume.
C
double the original volume.
D
four times the original volume.
11. The pressure of the gas inside a scuba diver’s lungs changes from 80 kPa to 120 kPa. If
the diver’s lungs initially held 9 L of gas, their volume at this depth would be:
A
3 L.
B
4 L.
C
6 L.
D
9 L.
12. A rigid steel drum holds a fixed volume of gas at a certain temperature and pressure. In
order to halve the pressure of the gas inside the container, you could:
A
halve the amount of gas in the container.
B
halve the amount of gas, but double the absolute temperature.
C
double the amount of gas and double the absolute temperature.
D
double the absolute temperature.
13. Two litres of helium gas were measured at a temperature of 400 K and a pressure of
0.5 atm. If the temperature of the molecules is doubled while the pressure remains
constant, what volume will the gas occupy?
A
0.5 L
B
1L
C
2L
D
4L
14. A gas, originally at 100 mL at 27 ºC and 1.2 atm, expands to 105 mL at 1.65 atm. The
new temperature is:
A
360 ºC.
B
87 ºC.
C
187 ºC.
D
160 ºC.
15. A gas is trapped in a syringe with a heavy mass maintaining pressure on it. Its volume
does not increase when:
A
the amount of gas in the syringe is increased.
B
the syringe is heated.
C
the gas is changed to a different gas of different molar mass.
D
atmospheric pressure is suddenly decreased.
16. A gas in a sealed 2 L flask is at 20 ºC and 101.3 kPa. When the gas is heated to 50 ºC, the
pressure inside will be:
A
405.2 kPa.
© John Wiley & Sons Australia, Ltd
3
QUEENSLAND CHEMISTRY
B
C
D
202.6 kPa.
111.7 kPa.
94.8 kPa.
17. An element is said to exist in the gaseous state. This means that:
A
its boiling point is below 0 K.
B
its molecules are close together and fast moving.
C
it can be liquefied by increasing the pressure on it.
D
its molecular volume at 0 ºC and 101.3 kPa is 22.4 L.
18. The volume of gas in a free-moving glass syringe is increased from 100 mL to 110 mL by
increasing the:
A
pressure from 100 kPa to 110 kPa.
B
temperature from 20 ºC to 22 ºC.
C
temperature from 300 K to 330 K.
D
pressure and decreasing the temperature.
19. Molar volume at 25 ºC is:
A
the volume of one mole of the gas.
B
the volume of one molecule of the gas.
C
22.4 L for all gases.
D
different for each different gas.
20. 3.6 g of a gas occupied 2.0 L at 298 K and 101.3 kPa. This gas is:
A
hydrogen (H2).
B
sulfur dioxide (SO2).
C
carbon dioxide (CO2).
D
argon (Ar).
21. Two sealed flasks have identical volumes, are at the same temperature and contain
different gases at the same pressure of 101.3 kPa. The gas in flask X has mass 6.0 g; the
gas in flask Y has mass 12.0 g. It follows that:
A
X contains half as many molecules as Y.
B
Y contains half as many molecules as X.
C
X and Y contain the same number of molecules.
D
the volume of each flask is 22.4 L.
22. Calculate the temperature of 0.4 mol of gas at a pressure of 3 atm and a volume of 2 L.
23. An aerosol can of insect repellent has a volume of 120 mL. The contents exert a pressure
of 9.00 × 102 kPa at 25 ºC.
(a) How many particles are present in the can of deodorant?
(b) If the contents of the can are transferred to a 300 mL container, what will be the
temperature if the pressure drops to 3.5 × 105 Pa?
© John Wiley & Sons Australia, Ltd
4
QUEENSLAND CHEMISTRY
24. 4.25 g of a gas occupies a volume of exactly 2.00 L at STP.
mass
(a) Calculate its density (density =
).
volume
(b) What is its molecular mass?
25. An evacuated 200 mL flask has a mass of 84.8 g. It is filled with a gas at 17.0 ºC and
770 mmHg pressure. The flask then weighs 85.8 g. Calculate the molar mass of the gas.
26. A gas was collected in a 1.5 L glass bottle. The pressure was 1.5 atm at room temperature
(25 ºC). The bottle was then immersed in boiling water. What quantity related to the gas
would change? and by what percentage would it change?
27. A room measures 10 m × 3.5 m × 6 m. The temperature in the room is 22 ºC and the
pressure is 750 mm Hg. Ignoring the volume occupied by the furniture etc., and accepting
that the air is 20% oxygen, calculate the volume of oxygen in the room if the room was
at SLC.
28. Each time Sandy breathes, she inhales about 400 mL of air. Oxygen makes up about 20%
by volume of air. How many oxygen molecules does she inhale in one breath at 25 ºC and
1.0 × 104 Pa?
29. One of the reactions responsible for the brown haze in photochemical smog can be
represented by the following equation.
2NO(g) + O2(g)  2NO2(g)
Calculate the volume of NO2 formed from the reaction of 10 mL of NO with excess O2.
All volumes are measured at the same temperature and pressure.
30. An important step in the preparation of sulfuric acid involves the production of sulfur
trioxide (SO3) from sulfur dioxide (SO2) and oxygen.
2SO2(g) + O2(g)  2SO3(g)
(a)
If all volumes are measured at the same temperature and pressure, calculate the
volume of sulfur trioxide produced when 24.5 mL of sulfur dioxide is placed in a
container with 6.00 mL of oxygen. Assume that all the SO2 and O2 that can react
does react.
(b)
Calculate the total volume of all gases remaining in the container.
31. Hydrogen reacts with oxygen in the reaction:
2H2(g) + O2(g)  2H2O(g)
(a)
What volume of water vapour will be produced when 4.50 L of hydrogen reacts
with 10.5 L of oxygen?
(b)
What volume of oxygen will remain unreacted?
© John Wiley & Sons Australia, Ltd
5
QUEENSLAND CHEMISTRY
Notes:
© John Wiley & Sons Australia, Ltd
6