Paint Lab AP 1617.docx - u201cGreen Chemistryu201d The...

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“Green Chemistry” The Stoichiometry of Paints Introduction Malachite and verdigris, two copper-based pigments, are synthesized 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 emphasizing green chemistry. 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 the experiment before coming to the laboratory is emphasized as students must come up with timesaving strategies to finish both pigment syntheses in the time allotted. Vocabulary Stoichiometry Limiting Reactant Excess Reactant Theoretical Yield Experimental Yield Percent Yield Green Chemistry Background All paints contain pigment, 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. Copper sulfate is the starting material for the one-step synthesis of malachite and the three-step synthesis of verdigris. Malachite pigment is combined with egg yolk binder to make tempera paint. Greenish malachite, copper(II) carbonate hydroxide, CuCO 3 Cu(OH) 2 , occurs with copper ore deposits in many parts of the world. Malachite is a secondary mineral, created by a chemical reaction with minerals that have already formed, for instance, by the action of water containing carbon dioxide or dissolved carbonate minerals on primary copper-containing rocks. Verdigris (“green of Greece”) can be collected by scraping the colored crust from sheets of copper exposed to

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