Name Ideal Gas Law: Stoichiometry Objectives: 1. To measure the mass of gas prod

Question

Name 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 the percent of 4. To understand partial pressures and mole fractions of gases. Safety: Wear safety goggles 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 o.045 g Record the mass 2. Use a thistle tube to add 15 mL (t 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 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 at 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. 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 cylind room temperature water. Read and record the volume of gas in the eudiometer tube when the wate levels are the same inside and outside the tube. Notice the scale increases going down the tube 9. Repeat steps 1-8 for the second trial 10. Obtain the barometric pressure in the room and record it. 11. the of the the and ook ofthe vapor pressure of water for th Assume this is the temperature of the gas at the volume and pressure measured.

Explanation / Answer

Q1.

theoretical yield of H2 produced for each trial

the equation;

Mg(s) + 2HCl(aq) --> MgCl2(aq) + H2(g)

mol of Mg = mass/MW = 0.037/24.3 = 0.00152 mol of Mg

mol of Mg = mass/MW = 0.0348/24.3 = 0.00143 mol of Mg

since no data of HCl is added, assume it is in excess

so

theoretical mol of H2 produced, accordig to 1:1 ratio:

0.00152 mol of Mg --> 0.00152 mol of H2

trial1:

mass of H2 expected = mol*MW = 0.00152 *2 = 0.00304 g of H2

0.00143 mol of Mg --> 0.00143  mol of H2

trial2:

mass of H2 expected = mol*MW = 0.00143  *2 = 0.00286 g of H2

B)

calculate mol/grams of H2 actually produced

so... relate mol via ideal gas law

PV = nRT

P = must be pressure of gas!

so

Trial 1

Pgas = Ptotal - Pvapor (you have already this calculated)

so...

now,

T1 = 22.33+273 = 295.33 K

Trial 1:

n = PV/(RT) = 709.31*(41.7)/(62400*295.33 ) = 0.0016050 mol of H2

mass = mol * MW = 0.0016050*2 = 0.00321 g of H2

Trial 2:

n = PV/(RT) = 709.31*(37)/(62400*295.33 ) = 0.0016050 mol of H2

mass = mol * MW = 0.0014241*2 = 0.0028482 g of H2

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