Ideal Gas Law: Stoichiometry Objectives: 1. To measure the mass of gas produced using temperature, pressure, and volume.

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Ideal Gas Law: Stoichiometry Objectives: 1. To measure the mass of gas produced using temperature, pressure, and volume. 2. To calculate the theoretical yield of gas from starting quantities. 3. To determine the percent yield of gas. 4. To understand partial pressures and mole fractions of gases. Safety: Wear safety goggles and gloves. Hydrochloric acid is corrosive. Avoid contact, and wash thoroughly with water after any contact. Procedure: 1. Weigh a short strip of magnesium ribbon on an analytical balance. If the mass of the ribbon is greater than 0.045 g. shorten the ribbon to reduce its mass to 0.045 g or less. Record the mass. 2. Use a thistle tube to add 15 mL (± 1 mL) of 3 M hydrochloric acid to a eudiometer tube. 3. While holding the eudiometer tube at an angle to minimize the mixing of the acid at the bottom, add deionized water slowly to fill it within a centimeter of the end. 4. Bend the weighed magnesium strip and push it into the open end of the eudiometer tube (like a small spring) so that it will not fall out when the tube is inverted. 5. Finish filling the eudiometer tube completely with water so no air bubble will be trapped when the tube is inverted. Also add approximately 350 mL of tap water to a 400 ml beaker. 6. Using your index finger to fully cover the eudiometer opening, invert the tube into the beaker. Remove your finger when the tube opening is under water. If the ribbon falls out of the tube, seek assistance from the instructor. 7. Hold the eudiometer tube upright (either by hand or with a ring stand) until the magnesium ribbon completely reacts. Do NOT lean the tube against the faucet, etc. If the magnesium stays at the bottom of the tube, the reaction will run faster if the tube is tilted at about 30 degrees from vertical. If the magnesium ribbon floats inside the tube, it is probably better to hold the tube straight up. 8. When the reaction is complete, cap the eudiometer tube with your index finger and transfer the tube to the tall cylinder of room-temperature water. Read and record the volume of gas in the eudiometer tube when the water levels are the same inside and outside the tube. Notice the scale increases going down the eudiometer tube. 9. Repeat steps 1-8 for the second trial. 10. Obtain the barometric pressure and record it. 11. Measure the temperature of the water in the tall cylinder and look of the vapor pressure of water for that temperature. Assume this is the temperature of the gas at the volume and pressure measured. 5B

6. Using your index finger to fully cover the eudiometer opening, invert the tube into the beaker. Remove your finger when the tube opening is under water. If the ribbon falls out of the tube, seek assistance from the instructor. 7. Hold the eudiometer tube upright (either by hand or with a ring stand) until the magnesium ribbon completely reacts. Do NOT lean the tube against the faucet, etc. If the magnesium stays at the bottom of the tube, the reaction will run faster if the tube is tilted at about 30 degrees from vertical. If the magnesium ribbon floats inside the tube, it is probably better to hold the tube straight up. 8. When the reaction is complete, cap the eudiometer tube with your index finger and transfer the tube to the tall cylinder of room-temperature water. Read and record the volume of gas in the eudiometer tube when the water levels are the same inside and outside the tube. Notice the scale increases going down the eudiometer tube. 9. Repeat steps 1-8 for the second trial. 10. Obtain the barometric pressure and record it. 11. Measure the temperature of the water in the tall cylinder and look of the vapor pressure of water for that temperature. Assume this is the temperature of the gas at the volume and pressure measured. SB Data: Trial 1 Mass of magnesium ribbon 0.04209 Volume of gas collected 0.04319 44.32 21.8°C Temperature of the gas Barometric pressure Vapor pressure of water Partial pressure of hydrogen gas convert 6 atry 44,35 21.8°C 29.79 in Hg 19.59 forr Trial 2 29.79 in Hg 19.59 forr

Data Analysis: remember that report questions are individual work A. Based on the amounts of Mg and HCI used, calculate the theoretical yield of hydrogen gas for each trial. Note that this is a limiting reactant calculation! Use 15 mL for the HCI calculation. 1. Calculate the theoretical yield of hydrogen gas (in grams) for trial 1. 2. Calculate the theoretical yield of hydrogen gas in (in grams) for trial 2. B. Based on your measurements of the gas collected in the eudiometer, calculate the moles and grams of hydrogen actually produced in each trial. 1. Calculations for trial 1 (moles and grams):

B. Based on your measurements of the gas collected in the eudiometer, calculate the moles and grams of hydrogen actually produced in each trial. 1. Calculations for trial 1 (moles and grams): 2. Calculations for trial 2 (moles and grams): C. For each trial calculate the percent yield of hydrogen gas.

B. Based on your measurements of the gas collected in the eudiometer, calculate the moles and grams of hydrogen actually produced in each trial. 1. Calculations for trial 1 (moles and grams): 2. Calculations for trial 2 (moles and grams): C. For each trial calculate the percent yield of hydrogen gas.

D. Mole fractions, etc. Recall that the mole fraction (X) for a gas in a mixture can be calculated in two ways (n = moles): X₁² = na total and X₁ = Pa Ptotal 1. For trial 1, calculate the mole fraction of H₂ in the gas sample. 2. For trial 1, calculate the number of molecules of H₂ in the gas sample. 3. For trial 1, calculate the molarity of Hz in the gas sample. 4. For trial 1, calculate the mole fraction of water vapor in the gas sample.

5. For trial 1, calculate the number of molecules of water vapor in the gas sample. 6. For trial 1, calculate the density of water vapor in the gas sample (in g/L).