Reaction of Magnesium with Hydrochloric Acid

Purpose
To develop a method for measuring the volume of gas generated in a reaction between Mg and HCl.
To develop a relationship between the mass of magnesium reacted and the volume of hydrogen generated.
To acquire an understanding of limiting reactants.

Materials

plastic bin rubber hose glass bend 1.0 M HCl
100 mL graduated cylinder test tube (25 x 200 mm)  5.00 mL pipet 0.5 g Mg ribbon
ringstand and clamp 1-hole rubber stopper pipet filler tap water

Safety
Avoid skin contact with hydrochloric acid. Wear goggles at all times. Rinse skin thoroughly if contact is made. Hydrogen gas is flammable.

Groups
You will work in groups of 3-4, assigned at random or by the professor. One member of the group will be assigned as a project manager; one as a computer operator; one or two as a laboratory technician. See the group work page for more information.

Procedure
Design an apparatus that will enable you to collect and measure the volume of hydrogen gas generated using only materials found in the list above. To facilitate speedy collection of data, your group may choose to set up two separate sets of equipment. Check your system(s) for leaks or cracks. React eight different masses of magnesium in the range of 0.01 g to 0.10 g with exactly 5.00 mL of 1.0 M HCl in eight separate trials. To the extent possible, try to spread the masses of magnesium evenly over the entire range 0.01 g to 0.1 g. Continue collecting the hydrogen gas until there is no more than one bubble produced per minute. Repeat suspicious trials. Record the mass of Mg used (use an analytical balance) and the volume of hydrogen gas generated in each trial. For each trial, make a note if any magnesium metal remains.

Questions

  1. Using Excel, prepare a graph of the volume of hydrogen gas generated vs. the mass of the magnesium used, plotting only the points (do not connect the dots).
  2. Which reactant, if either, is the limiting reactant when smaller masses of magnesium are used? when larger masses of magnesium are used? Use the concept of limiting reactants to explain the shape of your graph.
  3. Using the necessary data from your results, use Excel to develop a mathematical relationship between the grams of Mg reacted and volume of H2 produced. Note: Use only the points that make an approximately straight line. If there is more than one linear portion on your graph, plot a trendline for the portion of the graph that is not "level".
  4. Based on your experiment, how many milliliters of H2 would be produced had 0.0400 g of Mg been reacted with 5.00 mL of 1.0 M HCl? What if 0.0800 g of Mg had been used? 0.120 g?
  5. Write a balanced chemical equation, including phase labels, of the reaction that took place in this experiment. Consult your text, if necessary. Hint: This is a single replacement reaction.
  6. Using your balanced equation, calculate the theoretical volume of hydrogen gas, in mL, that should be produced at at temperature of 0C and and a pressure of 760 mm Hg when 0.0400 g of Mg reacts. Note: 1 mol of any gas at a temperature of 0C and a pressure of 760 mm Hg has a volume of 22.4 L. How does this result compare to the volume calculated for 0.0400 g of Mg in Question #4 above?
  7. How would your results and your graph change, if at all, if the concentration of HCl was twice as large as was actually used in the experiment?
  8. There were, as in all experiments, some "uncertainties" in this lab. Explain some actual causes of error and/or inaccurate measurements. How could you design a future experiment to eliminate these?

Laboratory Report
Group laboratory report guidelines at http://webs.anokaramsey.edu/chemistry/Chem1061/Labs/Reports/GroupReports.htm.
You may choose to submit this report by paper or by email (using a filename convention of lastname1_lastname2_etc_lab5 and a subject line in your email of "Chem 1061 Lab: Limiting Reactant Lab").