Stoichiometry Lab
Aluminum metal reacts with hydrochloric acid to form hydrogen gas and an aluminum chloride
solution. In this investigation, you will predict the mass of hydrogen gas produced by a given amount
of reactants, then measure the amount, and compare them.
Hydrochloric acid is an aqueous solution of hydrogen chloride. The concentration is usually described
in terms of “moles per liter” which is abbreviated “mol/L” or “molar” or “M.” The most concentrated
hydrochloric acid is 12 M, but for safety reasons we will be using a solution that is 3.0 M.
Procedure
1.
2.
3.
4.
5.
6.
7.
Put on a pair of safety goggles, and open your lab notebook to a new page.
Obtain approximately 0.25 grams of aluminum foil. Record the exact mass, and tear it into tiny
pieces.
Put 50.0 mL of the hydrochloric acid into a small beaker. Record the mass of the beaker with
solution in it.
Place the foil pieces on the balance tray next to the beaker of acid, and record the total mass.
[If this total mass does not equal the sum of number 2 and 3, you should remeasure.]
With the beaker still on the balance, drop the foil into the acid and observe. What happens to
the overall mass?
When the aluminum is gone, record the final mass of the beaker with the solution.
Dispose of the materials in the beaker according to your teacher’s instructions.
Analysis
1.
2.
3.
4.
5.
6.
7.
Write the chemical equation for the reaction that took place. Don’t forget to include the states
of matter (s, l, g, or aq). Balance it.
Calculate the number of moles of (clean) aluminum used.
Predict the mass of hydrogen that should be produced by this much aluminum reacting.
Calculate the mass of hydrogen gas produced during your reaction.
Calculate the “percent yield” for your reaction. If your prediction (#3) and calculation (#5) were
the same, your percent yield was 100%.
Why was your percent yield what it was? In other words, if you got 100%, why was it so
perfect? If you got less than 100%, what happened?
Is it possible to get a yield of over 100%? Explain. If you do calculate a yield of over 100%,
what went wrong? Be specific!! Hint: it would be incorrect to say you calculated wrong,
because if you know you did the calculations wrong, you should recalculate!