McKeachie Chem 1B Winter 08 - Practice problems for midterm 1 1. A compound contains only C, H, and N and has 58.51 % C and 7.37 % H by mass. Helium effuses 3.20 times faster than the compound does. Determine the empirical and molecular formula of the compound. 2. An aerosol spray can contains 400. mL of compressed gas at a pressure of 5.20 atm. When all the gas is sprayed into a large plastic bag, the bag inflates to a volume of 2.14 L. What is the pressure of gas inside the plastic bag? 3. A 2.00 L sample of O2(g) was collected over water in a laboratory at 25 °C with a specialized hood over the collection device, keeping the total pressure over the experiment at 785 Torr. When the O2is dried (water vapor removed), the gas inside the collection device contracts to a volume of 1.94 L at 25 °C and 785 Torr. Calculate the vapor pressure of water at 25 °C. 4. “Relief valves” are gas connection devices which prevent the pressure from reaching above a preset maximum. If the pressure of a system reaches this preset limit, the valve will be
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