# written assignment 6: gases | Chemistry homework help

**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)*