WHLS / Conc Chem
Name:
Date
Per
LAB: Converting Copper – PERCENT YIELD
PURPOSE: In this lab, solid copper metal (Cu) will react with molecular oxygen gas (O2)
to produce solid Copper Oxide (CuO). Since oxygen is being added to the copper, the
mass will increase by the amount of oxygen that bonds to the copper. This chemical
change must obey the law of conservation of mass. Write the completely descriptive
BALANCED equation below. Afterwards, perform the procedures described and answer
the lab questions below.
PRELAB: Write a complete balanced equation for this reaction. Include the PHYSICAL STATES of all
substances (s, l, g, aq).
PROCEDURE:
1) Heat the crucible for two minutes to dry then cool for three minutes.
2) Using tongs, transfer the crucible to the balance. Measure and record the mass of
the empty crucible in the data table.
3) Add exactly 2.00 g of copper powder to the crucible. Record the mass of the
copper and crucible, then the mass of just the copper in the data table.
4) Note the physical appearance of the copper powder.
5) Light the Bunsen Burner and set up the crucible above the burner so that the hottest
portion of the flame touches the bottom of the crucible.
6) Continue heating the crucible for 14 minutes. Watch for signs of a chemical
change!
7) Allow the crucible to cool!; return to your seats.
8) Your teacher will tell you the mass of the newly produce copper oxide with the crucible so we don’t
have to wait for it to cool. Record in your data table.
9) Calculate the mass of the new product by subtracting the mass of the empty crucible from the mass of
the crucible and product.
10) Calculate the mass of oxygen that was added to the copper.
(HINT: mass of oxygen = mass of CuO produced – mass of Cu reacted)
DATA TABLE: (**denotes a CALCULATED VALUE)
Mass of empty crucible:
Mass of crucible + copper metal:
**Mass of copper metal:
Mass of CuO and crucible after heating:
**Mass of CuO produced:
**Mass of oxygen gas (O2) added to the dish:
(Mass of CuO produced – Mass of Cu metal)
POST-LAB:
1) To find the theoretical value / yield of Copper Oxide that should have been produced, place the
mass of your copper into the formula below, and multiply by 1.25.
THEORETICAL YIELD
= .
g Cu x (1.25) =
g CuO produced
2) Using the theoretical yield (calculated above in #1) and the actual yield of CuO produced in the lab
(see your data table), calculate the % yield and % error, including units. SHOW YOUR WORK!
% YIELD
=
actual yield
theoretical yield
% ERROR = │actual yield – theoretical yield │
theoretical yield
x
100
x 100%
=
=
3) Were the changes you observed from the copper to the NEW Product physical or chemical? (Explain
how you know!)
4) Did the copper atoms remain in the crucible? Explain.
5) How and why did the mass of the crucible contents change after heating? (Did they gain or lose
mass, and why?)
6) Classify each substance from this activity (listed below) as an element, compound, homogeneous
mixture, or heterogeneous mixture:
● Copper Metal (Cu) =
● Oxygen Gas (O2) =
● Copper Oxide after heating (CuO) =
● Cu and the CuO when you are only half way done reacting =
7) PRACTICE PROBLEM: A farmer expects to produce 150 tons of corn in a given year. Last season,
he produced 137 tons of corn. Calculate the percent yield and the percent error last season. SHOW
YOUR WORK!