CHEMISTRY LAB: IDENTIFYING AN UNKNOWN OXIDE
(OXIDELAB.DOC)
1. Introduction: The goal of this lab activity is to determine whether a copper oxide sample is
either copper(I) oxide or copper(II) oxide. To begin with you will dissolve the sample in
hydrochloric acid, converting the copper oxide to copper chloride. The second product is water.
Once the oxide has completely reacted, you will add a piece of aluminum, which will react with
the solution to produce copper metal and an aqueous aluminum chloride solution, AlCl3(aq).
You will filter out and dry the copper and then determine its mass. From the mass of copper and
the original mass of the copper oxide sample you started with, you can calculate the percent of
copper in that original sample. Using the formulas for the two possible oxides, you can calculate
the percent of copper in each. Comparing your results to these two possible outcomes, you
should be able to determine which oxide you were dealing with.
2. Safety: The hydrochloric acid is irritating to the skin and very hazardous to the eyes. In case
of contact, rinse it off immediately with lots of running tapwater. Contact lens wearers may
experience some irritation from the fumes in this lab. Wear goggles and a lab apron when doing
this lab. Clean up even the tiniest droplet with a damp sponge and rinse out the sponge. Return
the goggles to the sterilizer cabinet when you are done. Wash your hands before leaving the lab.
3. Equipment and Materials Needed:
a. From the prep area:
watch glass (small shallow round glass dish)
plastic forceps (plastic "tweezers")
one piece of filter paper
small plastic container of the oxide to analyze, labeled “copper(?) oxide”
small strip of heavy gauge aluminum foil, about 5 mm x 5 cm, recently
scrubbed to remove the aluminum oxide coating
reagent bottle of 6M hydrochloric acid (HCl)
b. From your lab station supply cupboard:
125-ml Erlenmeyer flask
glass dropper pipet (“medicine dropper”)
50-ml beaker (to hold the dropper pipet between uses)
100-ml beaker (in which the reaction will take place)
250-ml beaker (used to hold the watch glass in the oven)
glass stirring rod
small plastic funnel
c. From the lab station supply drawer:
stainless steel “scoopula” (the one without the handle is more convenient)
d. At your lab station bench:
distilled water wash bottle
hotplate (optional)
e. For common use in the lab:
electronic balance with milligram precision
microwave oven (optional)
drying oven set on 200 degrees Fahrenheit
oven tongs and a ceramic fiber hotpad to protect the benchtop
4. Procedure:
DAY #1
a. Put on your apron and goggles. Leave them on until the lab is over.
b. Use a pencil to mark a clean dry 100-ml beaker with your lab group number or initials.
Weigh the empty beaker on the electronic balance and record that mass. Add about one-half
gram of the oxide and reweigh. Record that mass. (Use the data section, paragraph 5, below.)
c. Working over a piece of white paper, add about 5 ml of the hydrochloric acid to the
beaker. This is about three dropperfuls of acid. Swirl carefully and observe the effect of the acid
on the oxide. Feel the outside of the beaker for other evidence of a chemical reaction.
d. Form the piece of aluminum into a coil (like the mainspring in a wind-up watch) so it
will fit into the beaker easily, but don’t put it in yet. (Don’t cut yourself!)
e. Slowly and carefully add distilled water one or two ml at a time until the volume is
approximately 10 to 15 ml. Swirl the beaker after each addition. Warming the beaker on a
hotplate (or in the microwave oven for 10 seconds) may help the oxide to dissolve.
f. When the oxide appears to have reacted with the acid completely (almost no solid
material left undissolved), the solution should be clear but intensely green in color. Using the
forceps, carefully lower the aluminum coil into the beaker and then drop it into the solution so
none of the solution gets on the forceps. If it does, wash the solution off the forceps and back
into the beaker with a small amount of water from the wash bottle.
g. Observe the reaction. Feel the outside of the beaker for other evidence of a chemical
reaction.
h. Every five minutes or so, hold the aluminum with the forceps and use the scoopula to
scrape off the solid which has formed on the aluminum. Return the aluminum to the solution to
continue reacting. Rinse any solid adhering to the forceps or scoopula back into the beaker with
distilled water. When no more reddish solid material forms, the reaction is complete. You may
add another aluminum strip if the first one dissolves and the solution still has color.
i. When you are sure the reaction is complete, again use the forceps and scoopula to
clean off all the solid material that formed on the aluminum, allowing it to remain in the solution
from which it formed. Remove the aluminum strip, rinsing it to wash all solid particles back into
the beaker. Rinse the forceps and scoopula one last time to wash any particles adhering to them
into the beaker. Examine the aluminum strip for signs of chemical attack and dispose of it in the
school trash can.
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Day 2 Procedure: Identifying an Unknown Oxide Lab
(continued from Day 1)
j. Using a pencil, label one piece of filter paper with your lab group number or
initials. Weigh this piece on the electronic balance and record its mass in the data section. Fold
it in half twice, and open it with three layers on one side, one on the other. This makes a filter
paper cone which just fits the funnel. Place the funnel in the neck of the clean dry Erlenmeyer
flask, and place the filter paper cone in the funnel. Dampen it with a quick spray from the wash
bottle to get it to stick in the funnel properly and tightly.
k. You want to collect and later dry the solid copper metal powder in the beaker, but you
must remove all the dissolved aluminum chloride. To do this you will “wash” the precipitated
copper with distilled water. Allow the copper to settle. Slowly and carefully pour off into the
filter almost all of the clear liquid above the copper. If a few particles of copper go into the filter,
that’s okay, but try to keep most of it in the beaker. This pouring-off is called “decanting.” Add
to the beaker about 10 ml of distilled water and swirl. Allow the copper to settle again and
decant the clear liquid into the filter. (The first portion should have drained into the flask by
now. If not, be patient. Do not overflow the filter.) Wash and decant one more time. For the
last time, use the stirring rod to crush and thoroughly mix all copper particles with the distilled
water wash. Rinse the particles sticking to the stirring rod into the beaker or the filter. Add the
entire contents of the beaker to the filter. Copper particles remaining behind in the beaker will
have to be washed out with a spray from the wash bottle. Get every single particle out of the
beaker and into the filter. Let the filter drain. Keep an eye on the liquid level in the flask. If it is
getting full and the filtered liquid (“filtrate”) is clear, you may pour it out into the sink. If
somehow copper particles have managed to slip past the filter and into the flask, you need to
collect them by careful filtration onto a pre-weighed filter paper. If you have torn the filter paper,
raise your hand and get help from the teacher on how to proceed.
l. Let the filter paper drain completely. Give it a rinse with distilled water. Let that drain
completely. Repeat this rinsing and draining procedure two more times. In the funnel now you
should have only paper, copper, and water. Carefully remove the wet filter paper and copper
from the funnel and place on the watch glass. Gently open it so the copper is in the middle of the
watch glass and the paper is lying open and fairly flat. Place the watch glass and its contents on a
250-ml beaker. Place this in the drying oven set on 200 degrees Fahrenheit to remove all the
moisture.
Day 3 Procedure- Identifying an Unknown Oxide Lab
m. When the copper is thoroughly dry, use tongs to remove the beaker and watch glass
from the oven and let them cool nearby. Using the electronic balance, determine the mass of just
the paper and the copper metal. Record that mass below. Save them until you are sure they do
not need to be re-weighed. After your calculations are complete and the questions are answered,
you may dispose of the filter paper and the copper metal product in the school trash can.
n. Clean and return all glassware and supplies. Wash your hands before leaving the lab.
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Identifying an Unknown Oxide Lab- Data Sheet
5. Data:
a. Mass of empty beaker:
__________ g
b. Mass of beaker and oxide:
__________ g
c. Mass of labeled filter paper:
__________ g
d. Mass of filter paper and copper metal product:
__________ g
6. Calculations. Show your work in the space provided. Use units and labels on numbers.
(For atomic masses, use these: Cu, 63.546; O, 15.9994.)
a. Calculate the percent copper in copper(I) oxide:
__________ %
b. Calculate the percent copper in copper(II) oxide:
__________ %
c. Calculate the mass of copper oxide used in your experiment:
__________ g
d. Calculate the mass of copper metal recovered in your experiment:
__________ g
e. According to your data, then, the sample contained what percent copper?
__________ %
7. Results. Based on your calculations, which oxide of copper did you start with?
____________________
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8. Analysis. Show your work in the space provided. Use units and labels on numbers.
a. Using the mass of your sample and the accepted percent composition, calculate the
mass of copper that could have been recovered from your sample.
__________ g
b. Comparing your experimentally determined percent composition to the theoretical
percent composition, what is your percent error?
__________ %
9. Questions:
a. Write a balanced chemical equation for each of these chemical reactions. Use the
abbreviations (s), (l), and (aq) as appropriate.
(1) copper(I) oxide and hydrochloric acid
_______________________________________________________________________
(2) copper(II) oxide and hydrochloric acid
_______________________________________________________________________
(3) copper(I) chloride and aluminum
_______________________________________________________________________
(4) copper(II) chloride and aluminum
_______________________________________________________________________
b. Review the procedure and your results. List some factors that might have contributed
to an error in the amount of the copper you recovered.
_______________________________________________________________________
_______________________________________________________________________
c. List some examples of evidence that a chemical reaction is occurring that you
observed in this lab.
___________________________________________________________________________
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