PSC20 – FC3 - Stoichiometry Lab
BACKGROUND: In this lab you will perform and study the reaction between
copper (Cu) and silver nitrate (AgNO3). You will find the mass of a sample of
solid silver nitrate and prepare a solution of it. You will also find the mass of a
piece of copper, place it in solution, and observe its behavior. By finding the
mass of the copper at the close of the experiment, you will be able to investigate
quantitatively the reaction that occurred. From this, we will write the chemical
equation for the reaction.
CAUTION: Silver Nitrate (solid and solution) will turn skin black. Be careful with
it!
PROCEDURE:
Day 1
Day 2
Day 3
A. Obtain a piece if copper, form a coil with it, and then find the mass.
B. Find the mass of a clean and dry 250 mL beaker. Weigh 0.50 g of silver
nitrate that is provided (You need to be very accurate with all
measurements).
C. Dissolve the solid AgNO3 in exactly 100. mL of water in the 250 mL
beaker (make sure to use distilled water). Stir gently until all of the AgNO3
has dissolved.
D. Place the copper into the beaker. Make sure that all of the copper is
under the surface of the solution. *Observe any changes that occur for the
next 10-15 minutes.
E. Label your beaker and then cover the beaker with a watch glass and
place it on the shelf indicated by your teacher where it will not be disturbed.
This will continue to react until the beginning of the next lab period.
F. Carefully retrieve the beaker and place it on the desk top. *Record all of
your observations at this time.
G. Use tongs to retrieve your copper and shake all of the crystals off of the
copper. Use your wash bottle of distilled water to spray off the crystals that
are still on the copper. Make sure to spray off the crystals into the beaker.
Set the copper aside to dry. Once the copper has dried, find the mass of the
copper.
H. Let the crystals settle in the beaker and carefully decant the solution
(Decant = to pour off the solution carefully down a stirring rod, leaving the
solid behind).
I. Wash the residue with about 10 mL of distilled water and then carefully
decant. Repeat this step 2 more times.
J. After washing, the residue must be set in the incubator to dry over night.
K. The next day, make sure that the contents of the beaker is dry. Find the
mass of it and make sure that you use the same balance that you used
earlier in the lab.
L. Put the dry solid into the marked container on the front bench.
M. Wash out all of the lab equipment that you used and return to your desk
to begin working on your lab.
DATA: Your table should include the following.
Day 1
Day 2
Day 3
Mass of copper before placing in solution
Mass of silver nitrate
Mass of clean and dry beaker
Mass of copper after reacting
Mass change of copper
Mass of beaker + dry solid
Mass of solid produced
CALCULATIONS:
1. Calculate the number of moles of copper which reacted (the mass change
that was measured in Day 2).
2. Calculate the number of moles of silver that was produced.
3. Calculate the ratio of moles of silver to the moles of copper that were
involved in the reaction.
molesAg
ie.
molesCu
4. Calculate the concentration (molarity) of your silver nitrate solution.
5. Use your calculations in # 1 and #2 to find the number of copper atoms
that reacted and the number of silver atoms that were formed.
6. Use the ratio you calculated in step 3 to rewrite the equation below.
_____ Cu (s) + _____ AgNO3 (aq)  _____ Ag (s) + _____ CuNO3 (aq)
7. Was copper or silver nitrate the limiting reagent in this lab? Prove this by
calculation and show all of your work. Find the theoretical yield for silver.
8. Using your mass of silver nitrate and mass of copper, used a balanced
equation to find the percent yield of silver in this lab.