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AP Chemistry Test Preview: Gases (Chapters 5)
W(g) + X(g)  Y(g) + Z(g)
__ 23. A hot-air balloon, shown above, rises. Which of
the following is the best explanation for this observation?
A. The pressure on the walls of the balloon increases
with increasing temperature.
B. The difference in temperature between the air inside
and outside the balloon produces convection
C. The cooler air outside the balloon pushes in on the
walls of the balloon.
D. The rate of diffusion of cooler air is less than that of
warmer air.
E. The air density inside the balloon is less than that of
the surrounding air.
__ 44. A rigid metal tank contains oxygen gas. Which of
the following applies to the gas in the tank when
additional oxygen is added at constant temperature?
A. The volume of the gas increase.
B. The pressure of the gas decreases.
C. The average speed of the gas molecules remains the
D. The total number of gas molecules remains the same.
E. The average distance between the gas molecules
__ 52. Under which of the following sets of conditions
could the most O2(g) be dissolved in H2O(l)?
Pressure of O2(g) Above Temperature of H2O
H2O(l) (atm)
(l) °(C)
__ 37. A sample of 3.30 grams of an ideal gas at 150.0
°C and 1.25 atmospheres pressure has a volume of 2.00
liters. What is the molar mass of the gas? The gas
constant, R, is 0.0821 L atm mol-1 K-1).
A. 0.0218 gram/mole
B. 16.2 grams/mole
C. 37.0 grams/mole
D. 45.8 grams/mole
E. 71.6 grams/mole
__53. Gases W and X react in a closed, rigid vessel to
form gases Y and Z according to the equation above. The
initial pressure of W(g) is 1.20 atm and that of X(g) is
1.60 atm. No Y(g) or Z(g) is initially present. The
experiment is carried out at constant temperature. What
is the partial pressure of Z(g) when the partial pressure of
W(g) has decreased to 1.0 atm?
A. 0.20 atm
B. 0.40 atm
D. 1.2 atm
C. 1.0 atm
E. 1.4 atm
__ 74. Which of the following gases deviates most from
ideal behavior?
A. SO2
B. Ne
D. N2
C. CH4
E. H2
__ 24. A sample of 0.0100 mole of O2 (g) is confined at
37° C and 0.216 atmosphere. What would be the pressure
of this sample at 15° C and the same volume?
A. 0.0876 atm
B. 0.175 atm
D. 0.233 atm
C. 0.201 atm
E. 0.533 atm
__ 45. A sample of an ideal gas is cooled from 50.0 °C to
25.0 °C in a sealed container of constant volume. Which
of the following values for the gas will decrease?
I. The average molecular mass of the gas
II. The average distance between the molecules
III. The average speed of the molecules
A. I only
B. II only
C. III only
D. I and III
E. II and III
__ 39. Samples of F2 gas and Xe gas are mixed in a
container of fixed volume. The initial partial pressure of
the F2 gas is 8.0 atmospheres and that of the Xe gas is 1.7
atmospheres. When all of the Xe gas reacted, forming a
solid compound, the pressure of the unreacted F2 gas was
4.6 atmospheres. The temperature remained constant.
What is the formula of the compound?
A. XeF
B. XeF3
D. XeF6
C. XeF4
E. XeF8
__ 33. A hydrocarbon gas with an empirical formula CH2
has a density of 1.88 grams per liter at 0°C and 1.00
atmosphere. A possible formula for the hydrocarbon is
A. CH2
B. C2H4
D. C4H8
C. C3H6
E. C5H10
C. [(0.08)(1.0)(1.5)] / [(3.0)(400)]
D. [(3.0)(0.08)(400)] / [(1.0)(1.5)]
E. [(3.0)(0.08)(1.5)] / (1.0)(400)]
__ 40. The system shown above is at equilibrium at 28
°C. At this temperature, the vapor pressure of water is 28
millimeters of mercury. The partial pressure of O2(g) in
the system is
A. 28 mm Hg
B. 56 mm Hg
D. 161 mm Hg
C. 133 mm Hg
E. 189 mm Hg
__ 24R. A sample of 0.010 mole of oxygen gas is
confined at 127 °C and 0.80 atm. What would be the
pressure of this sample at 27 °C and the same volume?
A. 0.10 atm
B. 0.20 atm
D. 0.80 atm
C. 0.60 atm
E. 1.1 atm
__ 52. When dilute nitric acid was added to a solution of
one of the following chemicals, a gas was evolved, This
gas turned a drop of limewater, Ca(OH)2, cloudy, due to
the formation of a white precipitate. The chemical was
A. household ammonia, NH3
B. baking soda, NaHCO3
C. table salt, NaCl
D. epsom salts, MgSO4 . 7H2O
E. bleach, 5% NaOCl
__ 64. At 25 °C, a sample of NH3 (molar mass 17 grams)
effuses at the rate of 0.050 mole per minute. Under the
same conditions, which of the following gases effuses at
approximately one-half that rate?
A. O2 (32 g/mol)
B. He (4.0 g/mol)
D. Cl2 (71 g/mol)
C. CO2 (44 g/mol)
E. CH4 (16 g/mol)
S8(s) + 8 H2(g)  8 H2S(g)
__ 63. When 25.6 g of S8(s) (molar mass 256 g mol-1)
reacts completely with an excess of H2(g) according to
the equation above, the volume of H2S(g), measured at
0°C and 1.00 atm, produced is closest to
A. 30 L
B. 20 L
D. 5 L
C. 10 L
E. 2 L
__ 37R. A sample of 3.0 grams of an ideal gas at 121 °C
and 1.0 atmosphere pressure has a volume of 1.5 liters.
Which of the following expressions is correct for the
molar mass of the gas? The ideal gas constant, R, is 0.08
(L-atm) / (mol K).
A. [(0.08)(400)] / [(3.0)(1.0)(1.5)]
B. [(l.0)(l.5)] / [(3.0)(0.08)(400)]
Question 16 refers to various points in time during an
experiment conducted at 1.0 atm. Heat is added at a
constant rate to a sample of a pure substance that is solid
at time to. The graph below shows the temperature of the
sample as a function of time.
__ 16. Time when the root-mean-square speed of the
particles is greatest.
A. t1
B. t2
D. t4
C. t3
E. t5
__ 26. In a laboratory, a student wants to quantitatively
collect the H2 gas generated by a redox reaction The
student sets up the apparatus to collect the H2 gas over
water (see page 196). The volume of collected gas is
slightly higher than expected for the predicted yield of
H2. What could be the cause of this?
A. H2 is very soluble in water
B. the gas is produced at a low pressure
C. there is water vapor in the volume of collected gas
D. the pressure inside the collection chamber is greater
than the atmospheric pressure
E. some of the H2 produced effused out of the container
__ 31. At which temperature and pressure would a real
gas be most likely to deviate from ideal behavior?
Temperature (K)
Pressure (atm)
0.35 mol
0.90 mol
0.25 mol
__ 29. Three gases in the amounts shown in the table
above are added to a previously evacuated rigid tank. If
the total pressure in the tank is 3.0 atm at 25°C, the
partial pressure of N2(g) in the tank is closest to
A. 0.75 atm
B. 0.50 atm
(D) 0.25 atm
C. 0.33 atm
(E) 0.17 atm
__ 41. At approximately what temperature will 40. g of
argon gas at 2.0 atm occupy a volume of 22.4 L?
A. 1,200 K
B. 600K
(D) 270 K
C. 550 K
(E) 140 K
Questions 72 -73 refer to the gases below.
A. Cl2(g)
B. NO(g)
C. H2S(g)
(D) HCN(g)
(E) PH3(g)
__ 72. Of the following gases, which has the lowest
average molecular speed at 298 K?
__ 73. Which of the gases would have the highest rate of
effusion at 298 K?
Gases, Liquids and Solids: Take Home FRQs
2006.3. Answer the following questions that relate to the analysis of chemical compounds.
a) A compound containing the elements C, H, N, and O is analyzed. When a 1.2359 g sample is burned in
excess oxygen, 2.241 g of CO2(g) is formed. The combustion analysis also showed that the sample
contained 0.0648 g of H.
Determine the mass, in grams, of C in the 1.2359 g sample of the compound.
(ii) When the compound is analyzed for N content only, the mass percent of N is found to be 28.84 percent.
Determine the mass, in grams, of N in the original 1.2359 g sample of
the compound.
(iii) Determine the mass, in grams, of O in the original 1.2359 g sample of the compound.
(iv) Determine the empirical formula of the compound.
b) A different compound, which has the empirical formula CH2Br , has a vapor density of 6.00 g L1 at 375 K
and 0.983 atm. Using these data, determine the following.
The molar mass of the compound
(ii) The molecular formula of the compound.
2005B.6. Consider two containers of volume 1.0 L at 298 K, as shown below. One container holds 0.10 mol
N2(g) and the other holds 0.10 mol H2(g) The average kinetic energy of the N2(g) molecules is 6.2 x 10-21 J.
Assume that the N2(g) and the H2(g) exhibit ideal behavior.
a) Is the pressure in the container holding the H2(g) less than,
greater than, or equal to the pressure in the container
holding the N2(g)? Justify your answer.
b) What is the average kinetic energy of the H2(g) molecules?
c) The molecules of which gas, N2 or H2, have the greater
average speed? Justify your answer.
d) What change could be made that would decrease the average kinetic energy of the N2(g) molecules in the
e) If the volume of the container holding the H2(g) was decreased to 0.50 L at 298 K, what would be the
change in each of the following variables? In each case, justify your answer.
i) The pressure within the container.
ii) The average speed of the H2(g) molecules.
Answer the following questions related to hydrocarbons.
Determine the empirical formula of a hydrocarbon than contains 85.7 percent carbon by mass.
The density of the hydrocarbon in part (a) is 2.0 g L-1 at 50 oC and 0.948 atm.
Calculate the molar mass of the hydrocarbon.
Determine the molecular formula of the hydrocarbon.
Two flasks are connected by a stopcock as shown at right. The 5.0
L flask contains CH4 at a pressure of 3.0 atm, and the 1.0 L flask
contains C2H6 at a pressure of 0.55 atm. Calculate the total
pressure of the system after the stopcock is opened. Assume that
the temperature remains constant.
Octane, C8H18(l), has a density of 0.703 g mL-1 at 20 oC. A 255 mL sample of C8H18(l) measured at 20
C reacts completely with excess oxygen as represented by the equation below.
2 C8H18(l) + 25 O2(g)  16 CO2(g) + 18 H2O(g)
Calculate the total number of moles of gaseous products formed.
2004.8. Answer the following questions about carbon monoxide, CO(g), and carbon dioxide, CO2(g). Assume
that both gases exhibit ideal behavior.
a) Draw the complete Lewis structure (electron-dot diagram) for the CO molecule and for the CO2 molecule.
b) Identify the shape of the CO2 molecule.
c) One of the two gases dissolves readily in water to form a solution with a pH below 7. Identify the gas and
account for this observation by writing a chemical equation.
d) A 1.0 mole sample of CO(g) is heated at constant pressure. On the graph below, sketch the expected plot of
volume versus temperature as the gas is heated.
e) Sample of CO(g) and CO2(g) are placed in 1 L containers at the
conditions indicated in the diagram at right.
Indicate whether the average kinetic energy of the
CO2(g) molecules is greater than, equal to, or less than
the average kinetic energy of the CO(g) molecules.
Justify your answer.
(ii) Indicate whether the root-mean-square speed of the CO2(g) molecules is greater than, equal to, or less
than the root-mean-square speed of the CO(g) molecules. Justify your answer.
(iii) Indicate whether the number of CO2(g) molecules is greater than, equal to, or less than the number of
CO(g) molecules. Justify your answer.
Answer the following questions that relate to chemical reactions.
a) Iron (III) oxide can be reduced with carbon monoxide according to the following equation.
Fe2O3(s) + 3 CO(g)  2 Fe(s) + 3 CO2(g)
A 16.2 L sample of CO(g) at 1.50 atm and 200. oC is combined with 15.39 g of Fe2O3(s).
How many moles of CO(g) are available for the reaction?
(ii) What is the limiting reactant for the reaction? Justify your answer with calculations.
(iii) How many moles of Fe(s) are formed in the reaction?
b) In a reaction vessel, 0.600 mol of Ba(NO3)2(s) and 0.300 mole of H3PO4(aq) are combined with deionized
water to a final volume of 2.00 L. The reaction represented below occurs.
3 Ba(NO3)2(aq) + 2 H3PO4(aq)  Ba3(PO4)2(s) + 6 HNO3(aq)
Calculate the mass of Ba3(PO4)2(s) formed.
(ii) Calculate the pH of the resulting solution.
(iii) What is the concentration, in mol L-1, of the nitrate ion, NO3-(aq), after the reaction reaches
2003.2. A rigid 5.00 L cylinder contains 24.5 g of N2(g) and 28.0 g of O2(g)
a) Calculate the total pressure, in atm, of the gas mixture in the cylinder at 298 K.
b) The temperature of the gas mixture in the cylinder is decreased to 280 K. Calculate each of the following.
The mole fraction of N2(g) in the cylinder.
(ii) The partial pressure, in atm, of N2(g) in the cylinder.
c) If the cylinder develops a pinhole-sized leak and some of the gaseous mixture escapes, would the ratio in
the cylinder increase, decrease, or remain the same? Justify your answer.
A different rigid 5.00 L cylinder contains 0.176 mol of NO(g) at 298 K. A 0.176 mol sample of O2(g) is added
to the cylinder, when a reaction occurs to produce NO2.
d) Write the balanced equation for the reaction.
e) Calculate the total pressure, in atm, in the cylinder at 298 K after the reaction is complete.
2003.6. For each of the following, use appropriate chemical principles to explain the observation. Include
chemical equations as appropriate.
a) In areas affected by acid rain, statues and structure made of limestone (calcium carbonate) often show signs
of considerable deterioration.
b) When table salt (NaCl) and sugar (C12H22O11) are dissolved in water, it is observed that
both solutions have higher boiling points than pure water, and
(ii) the boiling point of 0.10 M NaCl (aq) is higher than that of 0.10 M C12H22O11 (aq).
c) Methane gas does not behave as an ideal gas at low temperatures and high pressures.
d) Water droplets form on the outside of a beaker containing an ice bath.
2002B.2 A rigid 8.20 L flask contains a mixture of 2.50 moles of H2, 0.500 mole of O2, and sufficient Ar so that
the partial pressure of Ar in the flask is 2.00 atm. The temperature is 127 oC.
a.) Calculate the total pressure in the flask.
b.) Calculate the mole fraction of H2 in the flask.
c.) Calculate the density (in g L-1) of the mixture in the flask.
The mixture in the flask is ignited by a spark, and the reactions represented below occurs until one of the
reactants is entirely consumed.
2H2(g) + O2(g)  2H2O(g)
d.) Give the mole fraction of all species present in the flask at the end of the reaction.
2002.3 Consider the hydrocarbon pentane, C5H12 (molar mass 72.15 g).
a.) Write the balanced equation for the combustion of pentane to yield carbon dioxide and water.
b.) What volume of dry carbon dioxide, measured at 25 oC and 785 mm Hg, will result from the
complete combustion of 2.50 g of pentane?
c.) The complete combustion of 5.00 g of pentane releases 243 kJ of heat. On the basis of this
information, calculate the value of H for the complete combustion of one mole of pentane.
d.) Under identical conditions, a sample of an unknown gas effuses into a vacuum at twice the rate that
a sample of pentane effuses. Calculate the molar mass of unknown gas.
e.) The structural formula of one isomer of pentane is
shown at right. Draw the structural formulas for the
other two isomers of pentane. Be sure to include all
atoms of hydrogen and carbon in your structures.
H – C – C – C – C – C – H