9-mw-of-a-gas - CHM151LL MOLAR MASS OF A GAS | 1 Molar Mass...

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CHM151LL: MOLAR MASS OF A GAS | 1 Molar Mass of a Gas OBJECTIVES: Become familiar with uses of the ideal-gas approximation Practice mass, volume, and temperature measurement techniques Determine the molar mass of a gas by the Dumas method DISCUSSION: If you can measure the mass of a pure gas sample along with the state variables P, V, and T , you can determine the molar mass of the gas. PROCEDURE: In this lab exercise, you will use solid CO 2 (Dry Ice®) as the source of carbon dioxide gas. 1. Fit a clean, dry 250-mL Erlenmeyer flask with a clean, dry solid rubber stopper and mark the level of the stopper’s lower edge with a piece of label tape. Record the mass of the flask, stopper (and tape) to the full precision of the balance. 2. Measure and record the temperature of the air. Measure the barometric pressure with the aneroid barometer (or obtain the value from your instructor) and record it on the data sheet. Caution: Do not handle Dry Ice with bare hands—if your skin is even slightly moist you may suffer severe tissue damage by freezing! Use tongs or insulated gloves. Do not stopper the flask tightly when it contains Dry Ice or water: vapor pressures can rise so high that the flask may break, sending shards of glass flying in all directions! Only after the solid sublimes should you stopper the flask tightly. The lab must be adequately ventilated because excess CO 2 is asphyxiating. Check the fume hood’s operation. 3. Clean several small (total volume 2-3 cm 3 ) freshly broken Dry Ice pieces of any condensed or deposited water vapor, and place the pieces into your flask. Stopper the flask loosely to allow gas to escape as the solid CO 2 sublimes. Gently swirl the flask until the Dry Ice has completely sublimed and then push the stopper down to the level marked previously. Record
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9-mw-of-a-gas - CHM151LL MOLAR MASS OF A GAS | 1 Molar Mass...

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