 We're going to perform an experiment to determine the molar volume of hydrogen at STP. We're going to generate the hydrogen by the reaction of magnesium metal with hydrochloric acid. I have a small strip of magnesium metal that masses 0.0342 grams. I'm going to take the magnesium ribbon and wrap it with some copper wire. The copper wire does not react with hydrochloric acid, so it will not produce any hydrogen gas. The role of the copper wire is to hold the magnesium ribbon in place during the reaction. We have a gas collection tube that is graduated in milliliters and tens of a milliliter. I'm going to carefully add about 10 milliliters of 6 molar hydrochloric acid to the tube. The amount of hydrochloric acid is not critical, seeing how it will be in a very large excess. I will then completely fill the tube with water. I'm going to add the water carefully, keeping the tube inclined, so that the less dense water will float on top of the hydrochloric acid. We will now place the magnesium ribbon in the solution held in place by the copper wire. We'll place our finger over the mouth of the gas collection tube. We will invert the tube in a large beaker of water. The hydrochloric acid will now move down through the water because of its higher density. When hydrochloric acid reaches the magnesium metal, it will produce hydrogen gas. The hydrogen gas will be collected by displacement of water. Once the magnesium has completely reacted, we'll let the hydrogen gas stand for a few minutes so that it reaches the same temperature as the surrounding air. We will now transfer the tube to a large water tank. We'll raise or lower the tube so the water level inside the tube and the water level outside the tube are the same. The outside pressure is the barometric pressure or the atmospheric pressure. The pressure inside the tube is the pressure of the hydrogen gas and the pressure of the water vapor. With the two water levels equal, we will read the volume of the hydrogen gas from the gas collection tube. We will correct for the pressure of the water vapor by measuring the temperature of the water in the water tank.