ChemCh11PracticeProblems

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Practice Problems Section 11.1
• You can convert pressure measurements
to other equivalent units.
• The method used to convert units of
measurement to other units is called
dimensional analysis.
• This method simply converts units by
multiplying a given value with one set of
units by a fraction that equals 1.
Practice Problems Section 11.1
Example:
• The reading of a tire-pressure gauge is 35.0
psi. What is the equivalent pressure in
kilopascals?
• Multiply 35.0 psi by a fraction that has the
units you want to go to over the units you
are trying to leave.
• The fraction should have a value of 1.
• 35.0 psi x 101.3 kPa/14.7 psi = 241 kPa.
• Multiply across the top and divide by the
value on the bottom.
Practice Problems Section 11.1
1. 59.8 in Hg to psi (1.00 in = 25.4 mm)
(59.8 in Hg) x (25.4 mm/1.00 in) x (14.7 psi/ 760
mm Hg) = 29.4 psi
2. 7.35 psi to mm Hg
(7.35 psi) x (760 mm Hg/14.7 psi) = 380 mm Hg
3. 1140 mm Hg to kPa
(1140 mm Hg) x (101.3 kPa/760 mm Hg) = 152
kPa
Practice Problems Section 11.1
4. 19.0 psi to kPa
(19.0 psi) x (101.3 kPa/14.7 psi) = 131 kPa
5. 202 kPa to psi
(202 kPa) x (14.7 psi/101.3 kPa) = 29.3 kPa
Practice Problems Section 11.2
11. Bacteria produce methane gas in sewage treatment
plants. This gas is often captured or burned. If a
bacterial culture produces 60.0 mL of methane gas at
700.0 mm Hg, what volume would be produced at 760.0
mm Hg?
• The pressure is increasing, so volume will decrease.
• If you want the volume to decrease, multiply the
volume by the smaller pressure over the larger
pressure.
• (60.0 mL) x (700.0 mmHg/760.0 mm Hg) = 55.3 mL
• Keep 3 significant figures and don’t forget the units!
Practice Problems Section 11.2
12. At one sewage treatment plant, bacteria cultures
produce 1000 L of methane gas per day at 1.0 atm
pressure. What volume tank would be needed to store
one day’s production at 5.0 atm?
• Pressure is increasing, so volume will decrease.
• Multiply the volume by the smaller pressure over the
larger pressure.
• (1000 L) x (1.0 atm/5.0 atm) = 200 L
• Keep 2 significant figures and don’t forget the units!
• Zeros are decimal place holders in this case. You can
also write it as: 2.0 x 102 L.
Practice Problems Section 11.2
13. Hospitals buy 400-L cylinders of oxygen gas
compressed at 150 atm. They administer oxygen to
patients at 3.0 atm in a hyperbaric oxygen chamber.
What volume of oxygen can a cylinder apply at this
pressure?
• Pressure is decreasing, so volume will increase.
• Multiply the volume by the larger pressure over the
smaller pressure.
• (400 L) x (150 atm/3.0 atm) = 20,000 L
• Keep 2 significant figures and don’t forget units.
• Zeros are decimal place holders in this case. You can
also write it as: 2.0 x 104 L.
Practice Problems Section 11.2
15. The volume of a scuba tank is 10.0 L. It contains a
mixture of nitrogen and oxygen at 290.0 atm. What
volume of this mixture could the tank supply to a diver at
2.40 atm?
• Pressure is decreasing, so volume will increase.
• Multiply the volume by the larger pressure over the
smaller pressure.
• (10.0 L) x (290.0 atm/2.40 atm) = 1208 L but you
can’t keep all those numbers as significant figures,
only 3 of them.
• The best answer is 1210 L or 1.21 x 103 L.
Practice Problems Section 11.2
16. A 1.00 L balloon is filled with helium at 1.20 atm. If
the balloon is squeezed into a 0.500 L beaker and
doesn’t burst, what is the pressure of the helium?
• Volume is decreasing, so pressure will increase.
• Multiply the pressure by the larger volume over the
smaller volume.
• (1.20 atm) x (1.00 L/0.500 L) = 2.40 atm
• You should have 3 significant figures, so you can add
a zero to the end of your answer.
• Don’t forget units.
Practice Problems Section 11.2
17. A balloon is filled with 3.0 L of helium at 310 K and 1
atm. The balloon is placed in an oven where the
temperature reaches 340 K. What is the new volume of
the balloon?
• The pressure measurement is extra information.
• Temperature is increasing, so volume will increase.
• Multiply the volume by the larger temperature over the
smaller temperature.
• (3.0 L) x (340 K/310 K) = 3.3 L
• You should have 2 significant figures.
• Don’t forget units.
Practice Problems Section 11.2
18. A 4.0 L sample of methane gas is collected at
30.0°C. Predict the volume of the sample at 0°C.
• All temperatures must be in Kelvins! Add 273.
• Temperature is decreasing, so volume will decrease.
• Multiply the volume by the smaller temperature over
the larger temperature.
• (4.0 L) x (273 K/303 K) = 3.6 L or 4 L
• You should have 1 significant figure.
• Don’t forget units.
Practice Problems Section 11.2
19. A 25 L sample of nitrogen is heated from 110°C to
260°C. What volume will the sample occupy at the
higher temperature?
• All temperatures must be in Kelvins. Add 273.
• Temperature is increasing, so volume will increase.
• Multiply the volume by the larger temperature over the
smaller temperature.
• (25 L) x (533 K/383 K) = 35 L
• You should have 2 significant figures.
• Don’t forget units.
Practice Problems Section 11.2
20. The volume of a 16 g sample of oxygen is 11.2 L at
273 K and 1.00 atm. Predict the volume of the sample
at 409 K.
• The mass and pressure measurements are extra
information.
• Temperature is increasing, so volume will increase.
• Multiply the volume by the larger temperature over the
smaller temperature.
• (11.2 L) x (409 K/273 K) = 16.8 L
• You should have 3 significant figures.
• Don’t forget units.
Practice Problems Section 11.2
21. The volume of a sample of argon is 8.5 mL at 15°C
and 101 kPa. What will its volume be at 0.00°C and 101
kPa?
• The pressure measurement is extra information.
• Temperatures must be in Kelvins. Add 273.
• Temperature is decreasing, so volume will decrease.
• Multiply the volume by the smaller temperature over
the larger temperature.
• (8.5 mL) x (273 K/288 K) = 8.1 mL
• You should have 2 significant figures.
• Don’t forget units.
Practice Problems Section 11.2
22. A 2.7 L sample of nitrogen is collected at 121 kPa
and 288K. If the pressure increases to 202 kPa and the
temperature rises to 303 K, what volume will the
nitrogen occupy?
• Pressure is increasing, so volume will decrease.
• Temperature is increasing, so volume will increase.
• Multiply the volume by the smaller pressure over the
larger pressure, and the larger temperature over the
smaller temperature.
• (2.7 L) x (121 kPa/202 kPa) x (303 K/288 K) = 1.7 L
• You should have 2 significant figures.
• Don’t forget units.
Practice Problems Section 11.2
23. A chunk of subliming CO2 (dry ice) generates a 0.80L sample of gaseous CO2 at 22°C and 720 mm Hg.
What volume will the CO2 have at STP?
• STP = 273 K and 760 mm Hg
• Pressure is increasing, so volume will decrease.
• Temperature is decreasing, so volume will decrease.
• Multiply the volume by the smaller pressure over the
larger pressure, and the smaller temperature over the
larger temperature in Kelvins.
• (0.80 L) x (720 mmHg/760 mmHg) x (273 K/295 K) =
0.70 L (You should have 2 significant figures.)
• Don’t forget units.

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