Written Assignment 6: Gases
Answer all assigned questions and problems, and show all work.
1. A gas occupying a volume of 725 mL at a pressure of 0.970 atm is allowed to expand at constant temperature until its pressure reaches 0.541 atm. What is its final volume?
(5 points)
(Reference: Chang 5.19)
2. The volume of a gas is 5.80 L, measured at 1.00 atm. What is the pressure of the gas in mmHg if the volume is changed to 9.65 L? (The temperature remains constant.) (5 points)
(Reference: Chang 5.21)
3. Why is the density of a gas much lower than that of a liquid or solid under atmospheric conditions? What units are normally used to express the density of gases? (5 points)
(Reference: Chang 5.30)
4. A sample of nitrogen gas kept in a container of volume 2.3 L and at a temperature of 32°C exerts a pressure 4.7 atm. Calculate the number of moles of gas present. (8 points)
(Reference: Chang 5.31)
5. What volume will 5.6 moles of sulfur hexafluoride (SF6) gas occupy if the temperature and pressure of the gas are 128°C and 9.4 atm? (8 points)
(Reference: Chang 5.33)
6. A gas-filled balloon having a volume of 2.50 L at 1.2 atm and 25°C is allowed to rise to the stratosphere (about 30 km above the surface of Earth), where the temperature and pressure are –23°C and 3.00 × 10–3 atm, respectively. Calculate the final volume of the balloon. (8 points)
(Reference: Chang 5.35)
7. A 2.10-L vessel contains 4.65 g of a gas at 1.00 atm and 27.0°C. (a) Calculate the density of the gas in grams per liter. (b) What is the molar mass of the gas? (10 points)
(Reference: Chang 5.47)
8. A certain anesthetic contains 64.9 percent carbon, 13.5 percent hydrogen, and 21.6 percent oxygen by mass. At 120°C and 750 mmHg, 1.00 L of the gaseous compound weighs 6.90 g. What is the molecular formula of the compound? (10 points)
9. What is the mass of the solid NH4Cl formed when 73.0 g of NH3(g) are mixed with an equal mass of gaseous HCl? What is the volume and identity of the gas remaining, measured at 14.0°C and 752 mmHg? (8 points)
(Reference: Chang 5.59)
10. A mixture of gases contains 0.31 mol CH4, 0.25 mol C2H6, and 0.29 mol C3H8. The total pressure is 1.50 atm. Calculate the partial pressures of the gases. (8 points)
(Reference: Chang 5.67)
11. Propane (C3H8) burns in oxygen to produce carbon dioxide gas and water vapor. (a) Write a balanced equation for this reaction. (b) Calculate the number of liters of carbon dioxide measured at STP that could be produced from 7.45 g of propane. (10 points)
(Reference: Chang 5.109)
12. A 10.0 g piece of pure aluminum is placed in 75.0 mL of 0.54 M hydrochloric acid at STP condition. They react as follows:
2Al + 6HCl → 3H2(g) + 2AlCl3
Calculate the following:
- Volume, in liters, of hydrogen gas. (5 points)
- Molarity of Al+3. (Assume 75.0 mL solution.) (5 points)
- Molarity of Cl–. (Assume 75.0 mL solution.) (5 points)
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