Equivalent Weight of Magnesium Experiment # 16

What we are doing today: We are going to verify the atomic mass of Magnesium. We are going to determine the # of moles of hydrogen displaced during a reaction. This will be accomplished using the Ideal Gas Law. Once we calculate the # of moles of Hydrogen produced we can calculate the # of moles of Mg that reacted. We will verify the atomic mass of magnesium by comparing the grams of Mg used to the number of moles of hydrogen displaced.

In order to use the Ideal gas law the Idea Gas Law PV=NRT In order to use the Ideal gas law the following information must be true: P pressure in atmospheres V volume in liters N number of moles R gas constant = 0.0821 L atm /mol K T temperature in Kelvin

Do NOT MIX THE WATER AND THE ACID. Mg + HCl → H2 + MgCl2 Procedure: Obtain and scrape with steel wool a 5 cm piece of Mg. do not touch the Mg until it has been weighed. Using a mg balance accurately determine the mass of the Mg. Coil the Mg around a pencil Add 10 of 6M HCl to your eudiometer tube. Slowly fill the tube with water. Do NOT MIX THE WATER AND THE ACID.

Procedures Continued Obtain a 1000 mL. beaker and fill it with water. Carefully lower the coil into the tube holding the string. Use your thumb to close the tube and then invert it. Place your tube in your 1000 mL. beaker and clamp it in place. Once your eudiometer tube is secured measure the amount of gas produced. Also measure the water column measurement in mm. Record the barometric pressure

Use my data as trial # 1 and you do two trials Mg mass = 0.040g Height of water = top of water to the gas line: 34.8 cm = 348 mm Water temp: 20 OC K = 273 + OC = 293 K Volume of H 2 collected = 47.0 mL from eudiometer tube Barometric pressure: 759 mm of Hg. # 4 # 2 # 5 # 6 # 1

Pressure of water column: must be in mm of Hg so we must convert from mm of H2O to mm of Hg 348 mm of H20 is the height of my water column Water vapor pressure (P H2O) see chart on pg 172 of lab book. My water temp was 20OC and my pressure is 17.5 mm of Hg #6 #8 #7

Pressure Dry H2 = PAtm - Pwater Vapor – P water column = 759 mm of Hg – 17.5mm of Hg - 25.58 mm of Hg = 715.92 mm of Hg .942 atms is the pressure of the dry H2 #9 To use the ideal gas law pressure must be in atms.

Now that we have pressure we can solve for moles of H2 produced :

# 13 on chart SHOW ALL WORK FOR FULL CREDIT 21.85 g/mole was the mass of Mg that I determined. The actual mass of Mg is 24.3 g/mole SHOW ALL WORK FOR FULL CREDIT