Lab Experiment 2: Copper Cycle
September 7, 2011
Overview
•
•
•
•
Purpose
Safety Precautions
Chemical Reactions
Experimental Procedure
Purpose
• Verify and understand the law of conservation
of mass.
• Observe chemical change through a series of
chemical reactions.
• Learn simple measuring techniques.
• Learn proper handling and disposal of
chemicals.
Safety Precautions
• Wear gloves and safety goggles
• Careful when handling nitric acid (avoid contact).
It can cause burns.
• Copper metal reacted with nitric acid produces
NO2, a red-brown toxic gas. The whole
experiment should be done in the hood.
• NaOH can cause burns (avoid contact).
• HCl is toxic by inhalation and corrosive to skin
and eyes (avoid contact).
Safety Precautions (cont.)
• Step 9 (addition of HCl with excess Zn)
releases H2 gas, which is flammable. Keep all
sources of heat away from this chemical
reaction.
• Acetone is also flammable, so keep away from
open flames and other sources of heat.
• Dispose of chemicals properly.
Chemical Reactions
• RXN 1: Cu(s)  Cu2+(aq) + 2e• RXN 2:
Cu2+(aq) + 2OH-(aq)  Cu(OH)2(s)
(precipitate)
• RXN 3:
Cu(OH)2(s) + ∆  CuO(s) + H2O(l)
• RXN 4: CuO(s) + H+(aq) + HSO4-(aq)  Cu2+(aq) +
SO42-(aq) + H2O(l)
Chemical Reactions (cont.)
• RXN 5: Cu2+(aq) + Zn(s)  Cu(s) + Zn2+(aq)
• RXN 6: Zn(s) + 2H+(aq)  Zn2+(aq) + H2(g)
Experimental Procedure
• Mass of a 250 ml beaker?
• Mass of a 250 ml beaker with ~1 g of copper
wire?
• Place them on a hotplate (turned OFF and in the
fume hood).
• Add 5 ml nitric acid to the copper sample and
cover the beaker with a watch glass.
• Gently heat the mixture until it becomes viscous
(turn the hotplate ON to 3).
Experimental Procedure (cont.)
• When it turns viscous, remove the beaker
from the hotplate and allow the mixture to
cool. MAKE SURE TO TURN OFF THE
HOTPLATE while waiting for the mixture to
cool! When the mixture is cool, add 10 ml D.I.
H2O and stir WITHOUT heat (use magnetic stir
bar and turn the stirrer on to 5).
• Then SLOWLY add 8 ml of 6 M NaOH with
continued stirring.
Experimental Procedure (cont.)
• Carefully add 50 ml D.I. H2O to it and heat to
boiling for several minutes (turn the hotplate
up to 8 or 9). Make sure to avoid splattering
of the beaker contents during the boiling
process.
• After any changes appear complete, continue
heating for another 5 to 10 minutes. Then
remove it from the hotplate.
Experimental Procedure (cont.)
• Then remove the beaker from heat.
• Carefully decant the liquid portion into another beaker.
Keep the solid! What does ‘decant’ mean?
• Add 25 ml D.I. H2O to the solid residue (then swirl but
keep beaker on bench) and make sure to wash the
sides of the beaker and decant the water. Do this step
one more time.
• Measure out 30 ml of 3 M H2SO4 and add to the solid
and gently heat until all of the solid has dissolved.
Remove beaker from the hotplate.
Experimental Procedure (cont.)
• Crease weighing paper to make an X (and tare) and
weigh out no more than 3 g of zinc metal and keep this
on the weighing paper. From here, use a scoopula to
add SMALL PIECES of Zn to the solution as necessary
until the solution becomes colorless (verify by holding
a white paper behind the beaker). Swirl the beaker
(keep it on the bench) after every addition of Zn. This
is when the redox reaction takes place.
• Decant the solution and keep the solid residue. Add 10
ml of 6 M HCl, which will cause a reaction with Zn2+.
Decant the liquid portion and keep the final product,
pure copper.
Experimental Procedure (cont.)
• Wash the pure copper with 2 portions of 50 ml
D.I. water and decant the liquid.
• Then wash the final copper product with ONE 20
ml acetone (modified) and make sure to also
wash the sides of the container, to completely dry
the water out.
• Decant the liquid out and keep the solid product
in the beaker. Let it air dry for a few minutes and
weigh the beaker containing the copper sample.