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Analytical balance, eudiometer tube (50-mL), one or mouth of eudiometer tube, ruler, 1000-mL beaker, 50-mL beaker, piece of thread about 25 cm in length, magnesium strips of 4.5 cm long (between 0.03-0.04 g each), 6 M HCl, deionized water Procedure Prepare your lab notebook to record your data. All data must be entered directly into your lab notebook using a black or dark-blue ink pen. 1. Under the "Data" section in your lab notebook, create a data table similar to the following: Trial #1 Trial #2 Mass of magnesium 0.0390 40.40 Volume of gas collected (mL) Height of water column (cm) (distance between water levels) Water temperature (°C) 15. 55 23.5 Barometric pressure (mm Hg)* 30.06 *Reference (State source of barometric pressure in the proper format) 126 0.0413 44.42 11.65 22.4
Experiment 10: MOLAR VOLUME OF A GAS Data and Results Date Name CHEM 131 Sec: Show your setups at every step. Remember to include units at all times. Use pencil. 1. Calculate the number of moles of gas from the mass of the magnesium using stoichiometry. Trial I Trial 2 2. Convert the volume of gas from mL. to L... Trial 1 Trial 2 3. Calculate the molar volume of the gas by dividing the volume by the number of moles of gas. Trial 1 Trial 2 4. Convert the height of water column from cm H₂O to mm H₂O, and then convert mm H₂O 1 mm Hg (where 13.5 has 3 sig. figs.) to mm Hg using the conversion factor: Trial 1 13.5 mm Hg H₂0 Trial 2 133
Experiment 10: MOLAR VOLUME OF A GAS 5. The barometric pressure is the pressure outside the tube, pressing on the surface of the water in the beaker. Since the level of the water inside the tube is higher than the level of the water in the be less than the pressure outside. We can calculate the pressure of the gas inside by subtracting the height of the water column (in mm Hg) from the barometric pressure (in mm Hg). Trial 1 Trial 2 6. The gas inside the be is wet because it is collected over water. The pressure is due to both the hydrogen gas and water vapor. In order to obtain the pressure of just the hydrogen gas, we must subtract the water vapor pressure from the total pressure inside the tube (from the step above). Look up the water vapor pressure from Table 10.1 for the temperature you measured and calculate the pressure of the hydrogen. Finally, convert the pressure into units of atm. Trial 1 Trial 2 7. Convert the temperature of the water to Kelvin (K). (T (K)-T (°C) + 273.15) Trial 1 Trial 2
Experiment U & Collect all the information you have at this point for the calculation of the molar volume of the gas at STP. (Hint: What does "molar" in "molar volume" mean? If you don't know you could be wasting time doing calculations with the wrong numbers! TRIAL I atm P₁- atm P₂- K T₂- K Ti- V₁- L/mol Calculate V₂, the molar volume at STP using the combined gas equation. (Remember to show units at every step.) TRIAL 2 atm PL- P₂= atm Ti- K T₂= K V₁ = L/mol Calculate V₂, the molar volume at STP using the combined gas equation. (Remember to show units at every step.) MO 9. Calculate the average molar volume at STP from your two trials. 10. Look up the commonly accepted molar volume of an ideal gas and calculate the error a percent error of your average value. Watch your sign and sig.figs. (Review Expt 2 for calculation.) Error = Percent Error =