AP Chemistry
Problem Set 9.2
Questions
1. Write the Ideal Gas Law. What is the value for R? What are the units of R?
2. What is the pressure on an ideal gas if 0.25 moles of it occupies 3 L at 300 K?
3. What volume does 50 grams of CO2 occupy if it is at 0oC and 700 mm Hg?
4. How many grams of CH4 are present if 300 mL of it is at 120 kPa and -25 oC?
5. What is the density of H2 gas at STP?
6. What is the density of air (assume 80% N2 and 20% O2) at STP?
7. What is the density of Xe gas at 22 oC and 740 mm Hg?
8. What is the molecular weight of a gas if 2.3 grams of it occupy 230 mL at a pressure of 750
mm Hg and a temperature of 75 oC?
9. A gas is 11.8% C, 69.6% Cl and 18.6% F. If 0.107 grams of it fills a 458 mL flask at 25 oC
at a pressure of 21.3 mm Hg, what is the molecular formula of the compound?
10. A gas is 25.2% S and 74.8% F. If 0.0955 g are put in an 89 mL flask at 45 oC and a pressure
of 83.8 mm Hg, what is the molecular formula of the gas?
11. State Dalton’s Law of Partial Pressures.
12. A container has 0.5 atm of H2, 2.5 atm of He, and 3 atm of O2. What is the Ptotal in the
container?
13. A container has 10 grams of N2, 100 grams of Xe, and 42 grams of Ar. What is the Ptotal in
the container if the volume is 4 L and the temperature is 50 oC?
14. A container has 20 grams of O2, 40 grams of CH4, and 10 grams of He at a Ptotal of 600 mm
Hg. What is the partial pressure of each gas?
15. Which of the following gases would be nearly impossible to collect over water? Why?
N2, HCl, NH3, Cl2
16. Hydrogen gas is collected over water at 15 oC. If the gas was collected at 800 mm Hg
atmospheric pressure, what pressure of H2 gas was collected?
17. Oxygen gas is collected over water at 22 oC. If the gas was collected in a 250 mL container
at 740 mm Hg atmospheric pressure, how many grams of oxygen were collected?
Answers
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PV = nRT R = 0.0821 Latm/molK
2.05 atm
27.65 L
0.28 grams
0.089 g/L
1.285 g/L
5.27 g/L
290 g/mole
Empirical CCl2F = 102 g/mole
MW = 204 so molecular = C2Cl4F2
10. Empirical SF5 = 127.1 g/mole
MW = 254 so molecular = S2F10
11. Ptotal= Σ Pindividual
12. Ptotal = 0.5 + 2.5 + 3 = 6 atm
13. nN2 = 0.357 moles
nXe = 0.762
Ptotal = 14.4 atm
moles nAr = 1.053
14. nO2 = 0.625 moles nCH4 = 2.5 moles
nHe = 2.5 moles
PO2 = (0.625/5.625)* 600 mm Hg = 66.7 mm Hg
PCH4 = (2.5/5.625)* 600 mm Hg = 266.7 mm Hg
PHe = (2.5/5.625)* 600 mm Hg = 266.7 mm Hg
moles ntotal = 2.17 moles
ntotal = 5.625 moles
15. HCl and NH3 would be nearly impossible to collect over water because
they are soluble in water. They will dissolve in it to make a solution so wouldn’t come out
the other end.
16. VPH2O at 15 oC = 12.8 mm Hg so PH2 = 800 -12.8 = 787.2 mm Hg
17. VPH2O at 19.8 mm Hg so PO2 = 740 – 19.8 = 720.2 mm Hg
0.313 grams of O2