Last updated 10-25-09
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Understanding Gases and Putting Gases to Work QUIZ
Brown nitrogen dioxide is responsible for the brown air in Phoenix. It comes from all of the automobile.
Problem 1: What is the molar mass of NO2?
Problem 2: Will it sink or rise in the air?
Problem 3: 520 gas cylinders containing 300,000 pounds of chlorine gas were used as a chemical weapon at Ypres, France in 1915. 5,000 soldiers died and 15,000 injured.
3a) Air weighs 28.8 grams per mole. How many grams per mole does chlorine gas (Cl2) weigh?
3b) Will chlorine gas stay close to the ground or rise up into the air?
3c) How many grams is 300,000 lbs mentioned above, knowing that 1 lb = 454 grams.
3d) How many moles of Cl2 is 300,000 lbs of Cl2? (use grams from 3c).
vacuum cleaner

Problem 4: What is the correct way of explaining how a vacuum cleaner works? (A or B?)

A) The spinning motor creates a partial vacuum which creates a suction effect and draws the dirt into the vacuum cleaner.
B) The spinning motor pushes air out of the vacuum cleaner reducing the number of collisions of air inside. The outside air molecules then collide more often which causes the air to rush in knocking dirt in as it goes.
balloons Problem 5: One morning your co-workers and you blow up about a hundred balloons with helium. You tie them together and left them all floating near the ceiling. A few hours later you peek through a window to the room and see all of them on the floor. They still look just as inflated as they did when they were blown up (no helium leaked out). You tell the coworkers not to go into the room and for sure do not light a match. The company you work at develops fuel cells. Why did the helium filled balloons fall to the ground?
pump Problem 6: On the right is an oxygen concentrator. It takes rooms air and filters out the nitrogen gas leaving pure oxygen gas for a patient to breathe. It starts by taking room air and pressurizing it. The pressurized gas is then passed through filters that let oxygen atoms pass but not nitrogen. Pressure is achieved with a pump. A piston starts 3 inches from the top of the cylinder and ends 1 inch from the top. If the pressure at 3 inches is 15 psi, what is the pressure at 1 inch?
Pressure Cooker

A few years ago a sad accident happened to a couple of college students. They learned about PV=nRT and wanted to see the pressure that dry ice would create in this pressure cooker. Unfortunately, the safety pressure release valve didn't work because the dry ice had created ice on the valve which blocked it. The pressure cooker exploded and killed both students. Again, we have to respect the pressure built up with liquids (or solids) turn into gases.
Problem 7: If a pound of dry ice was used and the pressure cooker has a volume of 6 quarts, what pressure in PSI could have occurred when all the dry ice turned to CO2 gas and reached a temperature of 70°F (cell P3)?

Like in the tutorial, if pressure is asked for, solve the PV=nRT formula for pressure, which you can see is P=nRT/V. This problem gets a bit more complicated because of the English measurement units need to be converted to metric units. See below table for setup help.
Below is a spreadsheet to help with the setup. The formula at I2 changes 70°F to Kelvin. The formula is worked so that nRT/V=P
 
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P
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R
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1  
n
R
T
/V
  
=P
2
pounds > grams
grams > moles (n)
R constant
70°F > Kelvin
Divide by volume
Atm > psi
pressure of CO2
3 1
lb
454
 g
1
 mole
0.0821
 atm·L
=(70-32)*5/9+273
 K    
1
 qt
14.7
 psi
=
???
 psi
4    
1
 lb
44.0
 g CO2   mole·K    
6.0
 qt
0.946
 Liters
1
 atm      

Problem 8: What units cancel in the above setup?
Problem 9: What unit or units remain?

Problem 10: What formula goes into R3?
midget basketball players

The results of a basketball game was called into question with allegations of the basketball being filled with a gas other than air. Your task is to investigate. The ideal gas law PV=nRT may help with some rearranging. Divide both sides by n gives PV/n=RT, now divide both sides by PV to get 1/n=RT/PV. Now multiply by both sides by grams to get g/n=gRT/PV.

"g/n" is grams per mole and that is what the Periodic Table lists for each element (atomic mass). So the final formula would read:
Atomic wt=gRT/PV
The standard radius of basketballs are 12.4 cm. Using formula for sphere V= 4/3 x pi x r3, you can calculate its volume. The pressure is 29.4 psi and the temperature is 81°F (27°C,300K) You weigh the basketball and it weighs 654.31 g. You let out the gas and find the empty weight as 600.00g.
(Hint: turn 29.4 psi to Atm (14.7psi=1atm), convert cm3 to liters, use Kelvin, and use 0.0821 for R).
Calculate gRT/PV and match it to the element that has that atomic mass. The below spreadsheet helps with the layout
With gRT/PV you can divide by the product of PV or divide by each of them separately. In spreadsheet format, I usually just divide by them separately. For pi you can use 3.1415 or In a spreadsheet, pi() returns the value of pi.
 
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1
g
R
T
/V
/P
= Atomic wt
2
654.31-600.00 g
R constant
Temp in Kelvin
Ball volume in cm3
 cm3 > L
Divide by volume
 psi > atm
g/mole=atomic wt
3
54.31
 g
0.0821
 atm·L
300.
 K    
1000
cm3
    
14.7
 psi
=
???
 g
4
 
mole·K    
=4/3*pi()*(12.4)^3
 cm3
1
L
29.4
 psi
1
 atm     mole
Problem 11: What is the volume of the ball in cm3 (G4)?
Problem 12: What cell cancels out the unit of "atm" in N4?
Problem 13: What is the g/mole in P3? (Note: That's the same as atomic wt)
Problem 14: What gas was used to fill the ball?
Problem 15: What formula is used in P3?
This table section is from the Handbook of Chemistry and Physics. It shows the pressure that a container holding water will exert at different temperatures. At the boiling point of water the pressure is 14.7 psi, which just enough to counter the pressure of the atmosphere, which is why water boils at 212°F or 100°C. Above those temperatures the pressure is more if in an enclosed container. Notice at 345.2°F (244°C) the pressure is 126.430 psi (6538.28 mm). That's over 8 times the pressure than at 212F. The pressure of water goes up exponentially as the temperature increases, which is why steam engines were so powerful.
Problem 16: This steam engine operates at 248°C and the piston it powers holds 1.25 liters of water vapor that fills and discharges 80 times per minute (80 revolutions/min). How many gallons of water does it need in an hour (60min) (cell V3)?
With gas problems, you always start with PV=nRT. There are no gallons in this formula, but there are moles (n), and we know we can turn moles of water to grams then grams to liters. So we rearrange PV=nRT to get PV/RT=n and go from there. See spreadsheet for layout help
First find grams of water vapor in the piston. Turn that into gallons of liquid water that can produce that many grams of water vapor, then multiply by the revolutions per minute times minutes.
 
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W
       
After this we have moles
H2O (n)
  
Now we have gallons of liquid water needed to fill a 1.25 Liter piston with water vapor per revolution.
              
1
P
V
/R
/T
Molar mass H2O
Total gallons of water to supply 1.25L piston with water vapor for 1 hr at 80rev/min at 248°C
2
From table at 248°C
Piston vol.
R constant inverted
divide by temp
248°C>Kelvin
moles> g
g > Liter
Liter > gal
3
138.848
 psi
1
 atm
1.25
 L   mole·K  
???
 g H2O
1
 Liter H2O
1
 gal
80
revs
60
 min = ??? gallons
4
 
14.7
 psi
 
0.0821
 atm·L
=248+273
K
1
mole
1000
 g H2O
3.785
 L
1
 min          

Problem 17: If the temperature was lowered to 240°C, which two cells would need to be changed? And what new value would go into A3?
Problem 18: If the steam engine ran at 75 revolutions per minute, what cell needs to be updated?
Problem 19: What is the formula that goes into V3? (As usual you can omit cells that have a "1" in them.)
Thanks for taclking this quiz. Send your answer to Ken Costello at chm151@chemistryland.com. Use subject title of "Gas Quiz". 
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Since Oct 26, 2009