Experimento

LABORATORY EXPERIMENT
pubs.acs.org/jchemeduc

Synthesis of Copper Pigments, Malachite and Verdigris: Making
Tempera Paint
Sally D. Solomon,* Susan A. Rutkowsky, Megan L. Mahon, and Erica M. Halpern
Department of Chemistry, Drexel University, Philadelphia, Pennsylvania 19104, United States
S
b Supporting Information

ABSTRACT: Malachite and verdigris, two copper-based pigments, aresynthesized in this experiment intended for use in a general chemistry
laboratory. The preparation of egg tempera paint from malachite is also
described. All procedures can be done with a magnetic stir plate, standard
glassware present in any first-year laboratory, and household chemicals. Yields
for the synthesis of malachite are about 95% making this an ideal activity for
courses emphasizinggreen chemistry. Typical results from students enrolled in
a general chemistry course are reported. While introducing the students to the
composition of artists’ paints, performing this experiment provides students an
opportunity to apply concepts in topics such as stoichiometry (excess reactants and yields), solubility, precipitation, and properties
of emulsions. The importance of reading theexperiment before coming to the laboratory is emphasized as students must come up
with timesaving strategies to finish both pigment syntheses in the time allotted.
KEYWORDS: First-Year Undergraduate/General, High School/Introductory Chemistry, Laboratory Instruction, Physical
Chemistry, Dyes/Pigments, Green Chemistry, Precipitation/Solubility, Stoichiometry, Synthesis

A

ll paints containpigment, which provides color, and a binder
(or medium), which suspends the pigments and binds them
to the surface of the object to be painted. Two paint pigments,
malachite and verdigris, are synthesized in this general chemistry
laboratory experiment and then a tempera paint is made using
malachite. While introducing the students to the composition of
artists’ paints, performing thisexperiment exposes students to
chemical concepts such as stoichiometry (excess reactants and
yields), solubility, precipitation, and properties of emulsions.
Copper sulfate is the starting material for the one-step
synthesis of malachite and the three-step synthesis of verdigris.
Both syntheses can be done with a magnetic stir plate, standard
glassware, and chemicals purchased from hardware storesand
supermarkets. The products are dried and weighed to determine
percent yields. Malachite pigment is combined with egg yolk
binder to make tempera paint. A version of the student write-up
for this experiment can be found in a laboratory manual that
contains standard first-year general chemistry experiments, all of
which can be done with household chemicals.1
The experiment was tested bystudents enrolled in a general
chemistry course. Knowing they would be required to finish both
syntheses in one lab period was a strong motivation for students
to read the experiment before coming to class to devise timesaving strategies. Results obtained from the class include time
required to finish both syntheses, yields of both pigments, as well
as the ideas used by students to make best useof their time.
This experiment can also be used to explore green chemistry.
Among the principles to classify a reaction as “green” are the use
of nonhazardous starting materials, their maximum incorporation into products, use of ambient temperature for energy
efficiency, and production of nontoxic products. The malachite
Copyright r 2011 American Chemical Society and
Division of ChemicalEducation, Inc.

synthesis, done at room temperature with household materials
and a yield of 95%, is suitable for a laboratory course emphasizing
green chemistry. Although verdigris is also made at ambient
temperature from similar household chemicals, their incorporation into the final product is reduced because the yields are much
lower (30À50%). Further, the copper acetate product is not as...