| Making
Lead Acetate
Christian Thorsten, CR
Scientific
WARNING:
This
procedure involves making soluble lead compounds,
which are very poisonous! If you choose to attempt
this experiments or procedure, you do so entirely at your own risk!
Lead acetate ( Pb(C2H3O2)2 . 3H2O) , or "salt of Saturn"
as alchemists and early chemists called it, finds use
in qualitative chemical analysis. It forms colored
complexes with some of the anthocyanin pigments (for
example, see http://www.crscientific.com/newsletter-10.html),
as well as producing colorful chromates, antimonates,
iodides, and other compounds. However, the individual
experimenter may have a difficult time obtaining lead
acetate.
There is a way to make small amounts
of this chemical with readily-obtainable materials.
It's quite simple but requires considerable time.
Vinegar.
Lead metal, preferably filings or thin shavings.
Petri dish with cover.
A great deal of time.
CAUTION:
Lead acetate is water soluble and toxic! The EPA discusses
various
hazards of lead acetate. Mallinckrodt Baker, Inc.
has published a very detailed Material
Safety Data Sheet about lead acetate that lists
various hazards to human health caused by lead poisoning.
You must wear eye-protecting goggles and vinyl or rubber
gloves when working with lead acetate. Disposable vinyl
gloves are good. Always work in a well-ventilated area
when making and experimenting with lead acetate. Lead
acetate must be stored in a tightly closed container
that is stored in a dry, ventilated area that is secure
from children. Containers used to store lead acetate
may remain contaminated after use.
Wear safety goggles at all times while preparing the
experiment, even when just looking at the dish to check
the progress of the reaction. Wear gloves when handling
the lead and the petri dish. Work in a well-ventilated
area and wash your hands thoroughly afterwards.
The lead shavings should be fresh,
without the dull-gray coating of oxidation that forms
after a short time.
Stronger (ca. 10-20%) acetic acid is
preferable to common vinegar, but the average individual
experimenter is lucky to have access to this.
Let's assume we're using vinegar, then:
1. Into the petri dish, pour the lead shavings.
2.Pour enough vinegar into the petri dish to cover the
lead shavings. It is best if air, vinegar, and lead
all share an interface (in other words, the lead should
protrude from the vinegar).
3. Make sure the vinegar doesn't evaporate completely
before it does its work on the lead metal. To get around
the latter problem, keep adding vinegar.
4. Do this for anywhere from a few months to a year.
The reaction can be speeded up by warming the dish with
a lamp no closer than about 15 cm ( 6 inches) from the
dish. The lamp may become contaminated and should be
used for lab use only. Use care to be sure the lamp
does not fall into the dish, its power cord is not hanging
loose, and that it is ventilated.
5. Periodically remove a drop of the
solution and place it on a microscope slide. Let it
evaporate and look for white crystals.When you're satisfied
with how much lead acetate has formed, evaporate the
solution to dryness. For best results, filter the lead
shavings out with a funnel and filter paper, putting
the filtrate into another (clean) petri dish before
evaporating. If desired, the lead acetate can
be re-crystallized once or twice more to purify it.
Figure 1 shows a vial of lead
acetate which the author produced from vinegar and chunks
of lead.
CAUTION:
Even a small vial of lead salts like the one in Fig.
1 should be stored in a tightly closed container
that is kept in a dry, ventilated area that is secure
from children. Containers used to store lead acetate
may remain contaminated after use. I stored the petri
dish in my lab where only I had access during the entire
time the reaction was taking place. A locked cabinet
that cannot be knocked over is acceptable, as long as
it is ventilated.
Upon exposure to air, lead acetate will absorb CO2
and become partially insoluble (see "lead acetate"
and "lead subacetate" in Merck Index (10th
edition)). Because of how the above method produces
lead acetate, there will invariably be some water-insoluble
matter in the final product. This is of no great consequence
for most qualitative chemistry experiments.
Lead acetate is useful for many chemistry
experiments. Again, you must be very careful with it.
Soluble lead salts are toxic, and some of them, including
this one, may also cause cancer.
Lead compounds disappeared from amateur chemistry
sets years before most other chemicals. Yet certain
hair-color products on the market today contain lead
acetate; then there's the matter of automobile batteries.
It seems there's been undue focus on chemistry sets
over the years for some perceived "frightening" quality
they somehow possess. Yet people have failed to look
around them at the everyday materials that are equally
or even more hazardous.
The singling-out and hobbling
of chemistry sets hasn't made the world much safer,
though it's certainly put a crimp in the aspirations
of many would-be scientists. Who knows where their experiments
could have led them if they hadn't become discouraged
at an early age by having little more than baking soda
and vinegar in their chemistry sets? Consider the alternative.
Instead of being allowed to experiment with a "dangerous"
chemistry set, today it's generally acceptable for young
people to take up what they think to be "safer" pastimes,
such as skiing, football, motocross, and rock fishing.
Merck Index,
10th Edition. Rahway, New Jersey: Merck and Company,
Inc., 1983.
Copyright
2005 by CR Scientific. The Society for Amateur Scientists
is grateful for permission to reprint this article.
This article otherwise remains copyright of CR Scientific
and may not be copied or distributed without prior written
permission (click here for contact info).
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