Chemistry Quiz June 7, 2010 Name:_________________________________________Score:______ 1. A sample of gas occupies a volume of 7. 50 L at 0. 988 atm and 28. 0 °C. (a) Calculate the pressure of the gas if its volume is decreased to 4. 89 L while its temperature is held constant. (b) At what temperature in degrees Celsius is the volume of the gas 4. 0 L if the pressure is kept constant. 2. Calcium carbonate, CaCO3(s), decomposes upon heating to give CaO(s) and CO2 (g). A sample of CaCO3 is decomposed, and the carbon dioxide is collected in a 250-mL flask.
After the decomposition is complete, the gas has a pressure of 1. 3 atm at a temperature of 31. 0 °C. How many moles of CO2 gas were generated? 3. An inflated balloon has a volume of 6. 0 L at sea level (1 atm) and is allowed to ascend in altitude until the pressure is 0. 45 atm. During ascent the temperature of the gas falls from 22°C to -21°C. Calculate the volume of the balloon at its final altitude. 4. What is the density of carbon tetrachloride vapor at 714 torr and 125°C? 5. A series of measurements are made in order to determine the molar mass of an unknown gas.
First, a large flask is evacuated and found to weigh 134. 567 g. it is then filled with the gas to a pressure of 735 torr and 31°C and reweighed; its mass is now 137. 456 g. Finally, the flask was filled with water at 31. 0 °C and found to weigh 1067. 9 g. (The density of water at this temperature is 0. 977 g/mL. ) Assuming that the ideal gas equation applies, calculate the molar mass of the unknown gas. 6. The safety air bags in automobiles are inflated by nitrogen gas generated by the rapid decomposition of sodium azide, NaN3: NaN3(s)>2Na(s) + 3 N2(g) If an air bag has a volume of 36 L and is to be filled with nitrogen gas at a pressure of 1. 15 atm at a temperature of 26. 0°C, how many grams of NaN3 must be decomposed? 7. A gaseous mixture made from 6. 00 g of O2 and 9. 00 g CH4 is placed in a 15. 0-L vessel at 0°C. What is the partial pressure of each gas, and what is the total pressure in the vessel? 8. A study of the effects of certain gases on plant growth requires a synthetic atmosphere composed of 1. 5 mol percent CO2, 18. 0 mol percent O2, and 80. 5 mo percent Ar. a) Calculate the partial pressure of O2 in the mixture if the total pressure of the atmosphere is to be 745 torr. (b) If this atmosphere is to be held in a 120-L space at 295 K, how many moles of O2 are needed? 9. An unknown gas composed of diatomic molecules effuses at a rate that is only 0. 355 times that of O2 at the same temperature. What is the identity of the unknown gas? 10. A scuba diver’s tank contains 0. 29 kg of O2 compressed into a volume of 2. 3 L. (a) Calculate the gas pressure inside the tank at 9. 0 °C. (b) What volume would this oxygen occupy at 26 °C and 0. 95 atm?
