Wednesday, August 10, 2011

Exercise (5.1 Gas)

1. A 452 mL sample of fluorine gas is heated from 22oC to 187oC at constant pressure. Calculate its final volume.

2. At a certain temperature and pressure, a glass bulb contains 1.25 g of nitrogen gas. If this glass bulb is now filled with argon gas at the same conditions of temperature and pressure, determine the number of atoms of argon in the glass bulb.

3. A 27.6 mL sample of PH3 (g) (used in the manufacture of flame-retardant chemicals) is obtained at STP.
    (a) Find the mass (in mg) of this gas.
    (b) How many molecules of PH3 are present?

4. A gas initially at 4.0 L, 600 torr, and 66oC undergoes a change so that its final volume and temperature become 1.7 L and 42oC. What is its final pressure? Assume that the number of moles of gas remain unchanged.

5. A small bubble rises from the bottom of a lake, when the temperature and pressure are 8oC and 6.4 atm, to the water’s surface, where the temperature is 25oC and pressure is 1.0 atm. Calculate the final volume (in mL) of the bubble if its initial volume was 2.1 mL.

6. Calculate the pressure (in atm) exerted by 2.12 mol of nitric oxide (NO) in a 9.0 L container at 76oC.

7. A gas has a density of 1.960 g dm-3 at STP. Determine its molar mass.

8. A cylinder of capacity 5.00 L contains 2.44 g of an unknown gas at a pressure of 3.00 atm and a temperature of 27oC.
   (a) Calculate the density of the gas.
   (b) Calculate the molar mass of the gas.
   (c) Identify the gas.

9. One of the important reactions in the nitrogen fertilizer producing process is the oxidising of ammonia.
          4NH3 (g) + 5O2 (g) → 4NO (g) + 6H2O (g)
   (a) If 3.00 L of ammonia at 802oC and 1.30 atm react completely with oxygen, find the volume (in litres) of water vapour produced at 125oC and 1.00 atm.
   (b) Find the volume of oxygen (in dm3) measured at 25oC and 90.7 kPa that will produce 100 dm3 of NO at 500oC and 100 kPa.

10. Find the required mass of KClO3 to produce 2.40 L of O2 gas that measured at a pressure of 1.0 atm and a temperature of 26oC. The reaction equation:
          2KClO3 (s) → 2KCl (s) + 3O2 (g)

11. The mass of a stopper-flask is 40.1305 g. When it is filled with X gas, the mass increases to 40.2487 g at 0.974 atm and 24.1oC. The flask is then fully filled with water. Its mass becomes 138.2410 g. If the density of water is 0.9970 g cm-3 at the same temperature, find the molar mass of X gas.

12. A mixture of gases contains 0.1 mol of CO2 and 0.3 mol of O2. Calculate the partial pressures of each component gases if the total pressure is 760 mmHg at a certain temperature.

13. A mixture of O2 and N2 in a 200 mL vessel exerts a pressure of 0.953 atm at 30oC. If there is 0.0020 mol of N2 present, calculate the
     (a) mole fraction of N2.
     (b) partial pressure of N2 (in atm).
     (c) partial pressure of O2 (in atm).
     (d) number of moles of O2.

14. A sample of ammonia gas, NH3 is completely decomposed to nitrogen and hydrogen gases over heated iron wool. If the total gas pressure produced is 866 mmHg, calculate the partial pressure of N2 and H2.

Calculate the partial pressure of helium and neon after the stopcock is opened if the temperature remains constant at 16oC.


Calculate the amount of H2 gas (in cm3) at 30oC and 90 kPa must be admitted to a 500 cm3 flask that contains N2 gas at 20oC and 100 kPa in order to increase the total pressure of the gas mixture to 110 kPa at 20oC.

17. A fixed volume flask has 1.35 mol of hydrogen gas at 1.05 atm and 25oC. Nitrogen gas is then added to the flask at the same temperature until the pressure rises to 1.64 atm. Calculate the mass of nitrogen gas added.

18. A cylinder with a movable piston records a volume of 12.6 L when 3.0 mol of oxygen is added. The gas in the cylinder has a pressure of 5.83 atm. When the cylinder develops a leak, the volume of gas is dropped to 12.1 L at the same pressure. Calculate the mass of oxygen escaped from the cylinder.

19. A sample of 1.49 g Ag2O decomposed upon heating and the product of oxygen gas was collected by displacement of water at 23oC and 750 mmHg. The reaction equation:
          2Ag2O (s) → O2 (g) + 4Ag (s)
If the vapour pressure of water at 23oC is 21.1 mmHg, calculate the volume of the oxygen gas produced in cm3.

20. Acetylene (C2H2), an important fuel in welding, is produced in the laboratory when calcium carbide (CaC2) reacts with water:
          CaC2 (s) + 2H2O (l) → C2H2 (g) + Ca(OH)2 (aq)
For a sample of acetylene that is collected over water, the total gas pressure (adjusted to barometric pressure) is 738 torr and the volume is 523 mL. At the temperature of the gas (23oC), the vapor pressure of water is 21 torr. Calculate the mass (in grams) of acetylene collected.

21. The alkaline metals (Group 1) react with the halogens (Group 17) to form ionic metal halides. Determine the mass of potassium chloride formed when 5.25 L of chlorine gas at 0.950 atm and 20oC reacts with 17.0 g of potassium.

1. 704.7 mL
2. 2.68 x 1022
3. (a) 41.9 mg
    (b) 7.4 x 1020
4. 1.31 x 103 torr
5. 14.25 mL
6. 6.75 atm
7. 43.90 g mol-1
8. (a) 0.488 g L-1
    (b) 4.004 g mol-1
    (c) He
9. (a) 2.17 L
    (b) 53 dm3
10. 7.99 g
11. 30.1 g mol-1
12. CO2: 190 mmHg
      O2: 570 mmHg
13. (a) 0.26
      (b) 0.249 atm
      (c) 0.704 atm
      (d) 5.65 x 10-3
14. N2: 216.5 mmHg
      H2: 649.5 mmHg
15. He: 0.16 atm
      Ne: 2.07 atm
16. 57.4 cm3
17. 21.2 g
18. 3.84 g
19. 81.34 cm3
20. 0.529 g
21. 30.9 g

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