Chapter 21 Laboratory: Synthesis of Useful Compounds 381
swirling, to the flask. (Caution: this process is extremely
exothermic. Add the sodium hydroxide slowly.)
- With both solutions at about room temperature, pour
the sodium hydroxide solution into the copper sulfate
solution, with stirring. The solution immediately turns
a milky powder-blue color as the two solutions react to
form a precipitate of insoluble copper(II) hydroxide.
- Rinse the 250 mL Erlenmeyer flask immediately and set
it aside to drain.
- Set up your filter funnel, using the 600 mL beaker as the
receiving container.
- Pour the blue mixture from the beaker into the filter
funnel. The blue precipitate is voluminous, so you may
have to use several pieces of filter paper to get all of it.
(I used 11 cm filter paper, and it took me three filtrations
to capture all of the precipitate. If you use 15 cm filter
paper, you may be able to get all of the precipitate in one
filtering pass.)
- When the filter paper fills with precipitate, allow the
remaining filtrate to drain into the receiving vessel and
then wash the filtrand with about 10 mL of water and
allow the water to drain.
- Transfer the filtrand, filter paper and all, to the 250 mL
Erlenmeyer flask. If you weren’t able to capture all of the
precipitate on one piece of filter paper, repeat steps 7
and 8 until you have transferred all of the precipitate to
the flask.
Measure about 70 mL of concentrated aqueous
ammonia, and add it to the 250 mL Erlenmeyer flask with
swirling. (The copper(II) hydroxide in the flask reacts with
the aqueous ammonia to form tetraamminecopper(II)
hydroxide, also known as Schweizer’s Reagent.)
Including the pieces you used to do the filtration, add
pieces of filter paper to the flask to a total of 5 pieces of 11
cm filter paper or 3 pieces of 15 cm filter paper. (The filter
paper provides the cellulose that will be dissolved by the
tetraamminecopper(II) hydroxide.)
Stopper the flask and set it aside to allow the
tetraamminecopper(II) hydroxide to dissolve the filter
paper. Swirl the flask periodically, and allow the reaction
to proceed for at least 24 to 48 hours.
Prepare about 300 mL of about 1.5 M sulfuric acid
solution in the 600 mL beaker. (Caution: this process is
extremely exothermic. Add the acid slowly to the water
with stirring.)
Pour the cellulose solution from the 250 mL Erlenmeyer
flask into the 250 mL beaker. If there is undissolved filter
paper in the flask, discard it.
Fill the syringe with the cellulose solution, submerge the
tip of the syringe in the sulfuric acid bath, and slowly
dISpoSAL:
The waste solution produced in this lab session is a
solution of copper sulfate in sulfuric acid. Neutralize
this solution by adding sodium carbonate or sodium
bicarbonate until all of the copper precipitates as blue
copper carbonate. discard the supernatant solution of
sodium sulfate by flushing it down the drain with plenty
of water. you can retain the crude copper carbonate for
later use or dispose of it with household solid waste.
expel a stream of cellulose solution into the sulfuric
acid. Refill the syringe and repeat until you have
transferred all of the cellulose solution to the sulfuric acid
bath. The threads and clumps of solid material
that appear are rayon.
Carefully pour off the liquid into a waste container,
retaining the raw rayon. Rinse the rayon several times
with tap water, discard the rinse water, and allow the
rayon to dry.
FIGURE 21-3: Dissolving cellulose (paper) in a solution of
Schweizer’s Reagent
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