Chem Lab

Gaseous Volume and Stoichiometry

Name______

Partners ______

Often reactions involving solid or liquid reactants produce gaseous products. As gases are generally not very dense, it is often easiest for chemists to measure the amount of gas produced by volume rather than mass. Using this measured volume and the ideal gas law you will determine the actual yield of hydrogen produced from the reaction of magnesium metal with hydrochloric acid. You will compare the actual volume of hydrogen produced to the theoretical yield of hydrogen produced and calculate the percentage error in your lab.

Materials:

250 or 400 ml beaker

one hole stopper for gas tube

50-mL or 100 mL gas collecting tube

Utility clamp

Beaker, 600 or 1000 mL

Thread or Wire

Ruler

Procedure:PRE-LAB: Expectation

a)You need to highlight all action terms and data to be recorded. YOU MUST KNOW EXACTLY WHAT TO DO in this lab. DO NOT hurt or burn your skin.

b)YOU MUST DRAW AN ILLUSTION and label how this apparatus will look like once you assemble the materials. *Draw and label on separate sheet of paper!

  1. Fill a 250 or 400 ml beaker with room temperature water.
  2. Record the temperature of the room and the barometric pressure in the data table.
  3. Cut a piece of magnesium ribbon about 6.0 cm long if you are using a 100.0 mL gas collecting tube and find its mass using the analytical balance. Record the mass in the data table.

OR Cut a piece of magnesium ribbon about 3.5 cm long if you are using a 50.0 mL gas collecting tube and find its mass using the analytical balance. Record the mass in the data table

  1. Wrap the magnesium ribbon into a circle around one of your fingers and tie a piece of thread about 6 inches long to the ribbon.
  2. Prepare a ring stand with utility clamp as shown to support the gas tube.
  3. Obtain a gas tube and one hole stopper. Pour about 20 ml of 3M HCl into the tube if using a 100.0 ml gas tube. OR Pour about 10 -12 mL of 3M HCl into the tube if using a 50.0 mL gas tube
  4. While tilting the tube, slowly fill it with room temperature water by pouring the water down the side of the tube to prevent mixing of the acid and water.
  5. Refill your beaker ¾ full with room temp water. With the tube completely filled with water, insert the magnesium about 3-4 cm into the tube. With the thread against the wall of the tube, insert the one hole stopper into the end of the tube, forcing all air and some excess water out of the tube. Make sure that there is no air in the hole in the stopper.
  6. With your finger over the hole in the stopper, invert the tube into the beaker of water (stopper down) and place the beaker/tube so that the tube can be held in position by the utility clamp. The reaction may not begin for a few moments while the acid flows down through the water and begins to react with the magnesium.
  7. When the evolution of gas has stopped, tap the side of the tube using a ruler or your finger to dislodge the gas bubbles clinging to the side of the tube.
  8. Place your finger over the hole in the stopper, undo the utility clamp and remove the tube from the beaker. Keeping your finger in place, move to the back sink and lower your tube, stopper down, into the large cylinder containing room temp water. Push the tube down into the cylinder until the level of liquid inside the tube is level with the water outside the tube. This assures that the pressure inside the tube is equal to the pressure outside. Read the volume on the tube to the nearest 0.1mL which will be the volume of the hydrogen gas plus the water vapor inside the tube. Record this volume in the table.
  9. Return to your lab station, remove the stopper and dump the contents of your tube into the sink. Clean up the station and return your equipment to the cart.

Data:

TemperatureoC
Temperature K
Atmos. Pressure(weather channel)
Mass Mg
Experimental Volume H2 produced(volume from step 11)
Vapor Pressure of H2O from chart
Partial Pressure PH2 dry

Calculations (Show setups and box final answers):

  1. Write the reaction equation for the reaction between magnesium and hydrochloric acid.
  1. Determine the number of moles of magnesium reacted in your lab.
  1. Determine the theoretical yield, in moles, of hydrogen gas from the reaction of your magnesium.Theoretical value for moles H2from stoichiometry
  1. Determine the partial pressure of the hydrogen in your tube.
  1. Using the Partial pressure of the dry gas and temperature and the ideal gas law, calculate the theoretical volume of hydrogen gas that should have been produced. Theoretical value for volume of H2using ideal gas law
  1. Using the partial pressure of the hydrogen and the measured volume, calculate the number of moles of hydrogen contained in our tube.Experimental value for moles using ideal gas law
  1. Calculate the percent error for both the moles and then the volumes. Are the values similar?

a)% error for hydrogen moles produced

b)% error for the hydrogen liters produced

Conclusion:

ESOE: